Using the Experimenter - Fascinating Electronics

Using the Experimenter - Fascinating Electronics
Using the
Experimenter
A Reference Manual and
Applications Guide
Version 1.0
Edition
Rev. B
by
Ronald M. Jac
kson
Jackson
Chief Engineer
Fascinating Electr
onics, Inc.
Electronics,
-1-
COPYRIGHT NOTICE:
The copyright of the circuit board, the firmware (software contained in
programmed memory), and this book are owned by Fascinating Electronics
Inc. They are protected by US and international copyright law. All rights
are reserved worldwide. You must not copy them, because you would then
be subject to legal action.
IMPORTANT NOTICE:
Because of possible variations in the quality and condition of materials and
workmanship, and variations in individual skill and prudence, Fascinating
Electronics Inc. disclaims any responsibility for the safe and proper
functioning of any projects or applications built using the Experimenter or
any component or product sold by us. You as the builder of the application
are responsible for the safe design and operation of what you have made.
You are responsible for determining that the Experimenter is suitable and
reliable enough for the task, and for meeting any applicable regulatory
requirements.
The Experimenter is not to be used in any application where its failure
could injure people or damage property. We especially do not want to
hear of Experimenters running Grandma’s pacemaker, cousin Edna’s iron
lung, or a nuclear power plant.
Fascinating Electronics Inc. disclaims any responsibility for incidental or
consequential damage resulting from the assembly or operation of any
component or product sold by us.
For more information about the Experimenter and our other products, please
write, call, or email:
Fascinating Electronics Inc.
925 SW 83rd AVE
Portland, OR 97225-6307
Call Toll Free (US and Canada) 1.800.683.5487
Direct Dial 503.296.8579
Email [email protected]
Copyright © 1992, 1993, 1995, 2001 by Fascinating Electronics Inc.
All Rights Reserved Worldwide
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Ta b l e o f C o n t e n t s
Introduction ...................................................................... 5
The Hardware ................................................................... 7
A Tour of the Photograph with Functional Overlay ........................ 7
A Tour of the Schematic .............................................................. 10
The Serial Connection ................................................... 13
The Physical Serial Connection ................................................... 13
Direct Communication .................................................................. 14
The Firmware .................................................................. 17
Help Features ..............................................................................
Command Syntax ........................................................................
Special Characters .......................................................................
Software Controlled Communication ............................................
Computer Program Template ......................................................
17
17
18
19
20
Command Tutorial ......................................................... 22
ANALOG Voltage Measurement ..................................................
COUNTER/TIMER Pulse Counting / Time Measurement ............
DIGITAL I/O Input and Output Digital Ports .................................
ENABLE-PWM Enable Drivers with PWM ..................................
FLIP-RELAY Switches Relay On and Off ...................................
GENERAL-INFORMATION/CONTROL .......................................
H-BRIDGE Control Motors ..........................................................
INDIVIDUAL-OUTPUT Controls Driver Outputs Individually ......
22
24
26
28
29
29
30
31
Command Reference ..................................................... 32
ANALOG Voltage Measurement ................................................. 32
COUNTER/TIMER Pulse Counting / Time Measurement ........... 33
DIGITAL I/O Input and Output Digital Ports ................................ 34
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Table of Contents
ENABLE-PWM Enable Drivers with PWM ..................................
FLIP-RELAY Switches Relay On and Off ...................................
GENERAL-INFORMATION/CONTROL .......................................
H-BRIDGE Control Motors ...........................................................
INDIVIDUAL-OUTPUT Controls Driver Outputs Individually ......
35
37
37
40
42
DC and Stepping Motors ............................................... 43
Driving DC Motors .......................................................................
Stepping Motor Coil Configurations .............................................
A Typical Stepping Motor .............................................................
Limiting Current with Series Resistors .........................................
Driving Higher Current Motors .....................................................
Applications of Computer Controlled Motors ................................
43
46
48
49
50
53
Using Analog Inputs ...................................................... 54
Scaling and Filtering .................................................................... 54
Dual Wiper Potentiometer ............................................................ 56
Prologue to the Applications ........................................ 58
An Ultrasonic RADAR .................................................... 59
The Ultrasonic Rangefinder .........................................................
Stepping Motor ............................................................................
Mechanical Assembly ..................................................................
RADAR Software .........................................................................
59
64
64
66
Observer Meteorological Station .................................. 68
Rugged Meteorological Instruments ............................................ 68
Meteorological Station Software .................................................. 72
An Autonomous Robot .................................................. 74
Hardware Features ...................................................................... 74
Mechanical Hints .......................................................................... 75
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0
I n t r o d u c t i o n
Let me tell you a story: How the Experimenter came about…
There was a time, not very long ago, before computers were in every home,
when people interested in science, technology, and electronics experimented
with transistors and ICs. High school and college students built interesting
semester projects. Grad students built equipment for their professors. Hobbyists
built projects and kits—things like digital clocks and shortwave radios. People
had fun, learned a lot, and their friends and associates were impressed with the
projects they built.
Then the microprocessor came along, and things got more complicated.
Yes, the personal computer offers incredible processing power so you can build
far more amazing gadgets than ever before. But as computers and software
became vastly more sophisticated it became a major project just connecting a
sensor or motor to the computer. You would spend most of your time building
the interface into the computer and creating driver software, and little time
creating the amazing gadget itself. It was like inventing the wheel, over and over.
If you went out to buy a device that provided this interface to your computer,
all you could find were industrial control boards. They are ridiculously expensive, and often perform just a single function. And an engineering degree is
required to figure out how to use these things.
We thought that while there are many problems in the world, this is one
problem we can most certainly cure. We set out to build a device that is easy to
use, with built-in intelligence to handle all the details so that no special software
drivers are required. A device that connects through a serial port, so that it will
work with any PC, Mac, notebook—just about any type of computer. A device
that provides a wide range of measurement and control capabilities: sensing
-5-
Chapter 0: Introduction
voltages, counting pulses and measuring signal timing, providing many high
current drivers for DC and stepping motor control, lots of digital I/O for
controlling logic devices, and even a high current relay. And we priced it to be
affordable for schools, hobbyists, and even industrial control engineers (it makes
life easier even for those who have engineering degrees). We call it the
Experimenter.
If you want to do something real with your computer, we have developed
some fascinating applications for the Experimenter. Here you will find a chapter
on an Ultrasonic RADAR (Application A), and a magnificent computerized
meteorological station (Application B). If you are creating your own computerized gadget, the Experimenter gives you a great head start. The autonomous
robot (Application C) was created by a team of high school students. Perseverance, research, and a significant head start from the Experimenter enabled them
to build a very sophisticated robot.
Today around the world, in university labs and in the field, Experimenters
are taking data. In factories Experimenters control industrial processes. In
private homes and at professional sites Experimenters are monitoring the
weather. At least one film studio is using Experimenters to control special
effects.
This book will explain the Experimenter to you—how it works, how to
connect it to your computer, the powerful commands it performs. You will learn
how to make time and voltage measurements (necessary for many types of
sensors). You’ll learn how to control motors, both ordinary DC motors and
stepping motors. How to output and read logic signals and how to flip the relay.
The Experimenter is like a “Swiss Army Knife” with many tools in one compact
package.
Ron
—Ronald M. Jackson
Chief Engineer
P.S. If you develop a nifty gadget that other Experimenter users may like
to build, please let us know. We can all benefit by sharing information. You can
send any comments you may have about the Experimenter directly to me at
Fascinating Electronics Inc. And especially let me know if there is any way we
can make the Experimenter more useful to you! Please email me at:
[email protected]
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1
The
Hardware
The Experimenter is a microcontroller with on-board software and special
measurement and control hardware. In this chapter, we’ll take a look at the
hardware, and learn some of how the Experimenter performs its many functions.
A Tour of the Photograph with Functional Overlay
Figure 1-1 is a photograph of the Experimenter, with an overlay of the
functions supported in each area. Let’s take a quick tour of the photograph to give
you a feel for the Experimenter. Starting in the upper-left corner of the board:
the logic supply provides +5 volts to run all of the logic circuitry on the
Experimenter. Below that is the “brains” of the Experimenter, the microcontroller
with its support circuitry.
In the upper-right corner is the RS-232C circuitry, providing communication between your computer and the Experimenter. The next chapter will discuss
communications in detail.
Below that is the relay
relay, which you can use to switch high current loads. To
the right is the digital I/O chip. This provides 24 bits of digital input or output,
for binary sensing or low current control.
Just left of the digital I/O chip are two driver chips with heatsinks. These
provide eight channels of high-current drive for DC and stepping motors,
solenoids, additional relays, and other power devices.
Most of the connections to Experimenter functions are located in the
measurement and control I/O area, below the microcontroller, drivers, and
digital I/O. Exceptions are IO1, the backup battery input; IO2, IO3, IO4, the relay
connections; and IO5 the ±10v boosted supplies.
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Chapter 1: The Hardware
Logic Supply
RS-232C
Microcontroller
Relay
Digital
I/O
Drivers
Measurement and Control I/O
Analog
Wiring Grid
Supply
Extra Connectors
Figure 1-1: Experimenter with Functional Overlay
The Experimenter provides an intelligent interface between any computer with
a serial port and a wide range of measurement and control functions. It is built
around a microcomputer, with a variety of additional support and interfacing
hardware. These include power supplies, RS-232C level shifters, high-current
devices, and many channels of digital I/O. A large wiring grid and pads for extra
connects enhance the ease-of-use in many projects.
-8-
Chapter 1: The Hardware
At the far left of the measurement and control I/O area are eight analog
inputs at IO6 ANALOG. These inputs can measure voltages with 5 mV
resolution. These are useful for many types of sensors, like temperature sensors
or photocells.
To the right of are four timer/counter inputs at IO8 T-IN. As the name
implies, these can be used to measure time intervals or count pulses. These
measurements have many applications. For example, counting raindrops in a
weather station, counting rotations of a shaft, or measuring distance using echo
ranging in an Ultrasonic RADAR.
Next are two pulse width modulator (PWM) outputs at IO9 PWM and eight
timed outputs at IO10 T-OUT. The PWMs are used to control the duty cycle
during which the drivers are enabled. This technique is often used to control the
speed of DC motors. The timed outputs are just the unbuffered versions of the
signals going to the drivers.
The driver outputs IO11 DRIVER-B AND IO12 DRIVER-A and IO13
DIGITAL-I/O are the remaining signals in the measurement and control I/O
area.
The Analog supply provides an adjustable reference power source for the
analog-to-digital converter on the Experimenter, and for use by any sensitive
analog circuits you may add to the board. This is adjusted to 5.120 volts so that
the 10-bit A/D step size is 5 mV. Jumper J12 lets you select between using this
supply or the logic supply to power the A/D converter.
To the right is a large wiring grid
grid. This is a great place to add your own
projects. To make wiring even easier the logic supply and ground are provided
to every fourth connection in the top and bottom rows in the grid. This
corresponds to the standard power pin locations of upper right corner for VCC and
lower left for VSS for most TTL logic ICs. Any chips that do not have this pinout
should be installed to the right or left of these connections.
Below the wiring grid are pads for mounting extra connectors: one high
density, one DB-25, two DB-9, and one 5 mm pitch terminal strip. You can add
any of these connectors to suit your particular applications. These connector
locations are marked X1 through X5
X5.
GND
GND
PLUS
PLUS
+
–
Center is +
–
+
Center is –
Figure 1-2: Polarity Selection
Jumper J1 is used to select the polarity
of the power connector. Set the jumpers
as shown for the power supply you are
using with the Experimenter. Power
supplies from Fascinating Electronics
Inc. are center+, as shown at left.
-9-
Chapter 1: The Hardware
A Tour of the Schematic
Though it may look intimidating at first, the Experimenter hardware is
actually fairly straightforward. Let’s go through the schematic, which is located
at the centerfold (pages 38-39) of this book. DC power of 5.5 to 15 volts enters
the Experimenter through connector P1 (schematic grid F-5). Since the center
contact on the power connector is positive on some power supplies, and negative
Figure 1-2
on others, jumper J1 provides a means to select between the types (Figure
1-2).
IO1 lets you add a backup battery (make sure the power supply voltage is greater
than the battery voltage). S1 provides a convenient power switch.
Voltage regulator U1 produces the logic supply. The logic supply provides
+5 volts to all of the logic circuitry on the Experimenter, with power left over
for additional circuitry. U1 is a low-dropout voltage regulator, permitting the
Experimenter to run off of a 6 volt battery. U1 is rated at 1 amp.
Low-dropout adjustable voltage regulator, U10, provides a separate analog
supply. In addition to providing an adjustable reference for more accurate
voltage measurements, the analog supply also provides “quiet” power for
sensitive analog circuits — power that is isolated from the relatively noisy logic
supply. If you build analog circuits, using this supply will help avoid many noise
problems and ease your debugging. This voltage regulator is also rated at 1 amp.
The “brains” of the Experimenter is the microcontroller, U6 (schematic grid
A-2). It is an eight bit microprocessor with additional measurement and control
hardware built in. The microcontroller includes a serial port, baud rate generator,
a clock oscillator, an analog multiplexer, analog-to-digital convertor, counters,
timers, and pulse-width-modulators.
Your computer connects to the Experimenter through P2 (grid E-1), a
standard 25-pin female connector. Since RS-232C uses larger voltage swings
than standard logic, U5 is required to interface the RS-232C signals to the
microcontroller. U5 also contains a voltage doubler and inverter that provides
the unregulated plus and minus 10 volts required for RS-232C. These voltages
are available for your use on IO5, but the current available is limited. The serial
connection will be described in detail in the next chapter.
A 7.3728 MHz crystal, Y1, clocks the microcontroller. This peculiar
frequency can be evenly divided into standard baud rates for RS-232C. Jumpers
J6 allows you to select rates from 300 baud to 38.4 kilobaud.
The analog multiplexer in the microcontroller provides eight analog voltage
measurement inputs (IO6, ANALOG 0:7). The analog-to-digital converter can
measure these inputs with 5 millivolt resolution (10 bits) over the range from 0
to 5.115 volts. This is useful for many sensors, like thermistors for temperature
measurement, or photocells for light sensing.
- 10 -
Chapter 1: The Hardware
2716
2732
2764
J2 J3
27128
J2 J3
27256
J2 J3
27512
J2 J3
J2 J3
J2 J3
J4 J5
J4 J5
J4 J5
J4 J5
J4 J5
J4 J5
Figure 1-3: EPROM Type Selection Jumpers
The Experimenter can accommodate six different types of EPROMS, ranging in
size from 2 kilobytes to 64 kilobytes. Configure jumpers J2-J5 as shown for the
particular type of EPROM you are using.
Capacitor C13 (grid E-7) provides a reset signal to the microcontroller and
to the parallel interface chip, U9. This causes the microcontroller and parallel
interface chip to initialize their internal registers when the logic supply is
switched on.
The lower eight bits of the address bus multiplex on the same lines as the
data bus. The octal latch, U2 (grid A-4), holds the address value while the data
is on the bus.
Software for the microcontroller is stored in an EPROM, U4 (grid A-6). The
Experimenter can accommodate many different types of EPROM chips. Jumpers J2 through J5 select between the different types. These jumpers should be set
for the type of EPROM that came with your Experimenter, usually a 27256
Figure 1-3
(Figure
1-3).
Though not currently used, the Experimenter has space for an additional
memory. U3 (grid A-7) can accommodate an 128 kB static RAM, which may be
accessed as four 32 kB banks.
The four counter/timer inputs (IO8, T-IN 0:3) connect directly to the
microcontroller. As with the analog multiplexer and analog-to-digital converter,
all counting and timing circuitry is within the microcontroller chip.
Eight precision timed outputs come directly from the microcontroller.
Timed outputs are available unbuffered (IO10, T-OUT 0:7). They are also
buffered to drive higher voltage and current applications by U7 and U8. Each of
these driver outputs (IO12, DRIVER-A 0:3 and IO11 DRIVER-B 4:7) can source
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Chapter 1: The Hardware
and sink up to 1 amp. That’s a lot of current! An external power source must be
provided for these drivers, since the logic supply isn't up to that kind of load.
Each driver has its own positive power input (+A and +B). These inputs must be
connected to a power source of from +4.5 to +36 volts DC. Switched unregulated
Experimenter power is available on the next pads to the left (SWP) and may be
used for this purpose. Additional grounding points are provided on the DRIVER
connections.
Pins 4, 5, 12 and 13 of the high current driver IC's (U7 and U8) solder to large
metal heatsinks to pull the heat of these high-power devices. Because of the
weight of these heatsinks the drivers should be secured to their sockets with a
nylon cable tie. Otherwise they might fall out of their sockets!
The drivers have built-in protection against getting too hot — they will shut
down if their internal temperature gets too high. They may, however, oscillate
as this temperature is reached. The drivers are not protected against short
circuits!
Using jumpers J8 through J10, you may either select to always enable each
pair of driver outputs (no jumper), or to enable them under the control of the pulse
width modulators (see Figure 1-4
1-4). The PWMs provide a continuous stream of
pulses of controllable frequency and duty-cycle. When enabled by the varying
duty-cycle from the PWMs, the driver outputs will provide varying amounts of
power to a load. For example, by controlling the PWM duty-cycle the speed of
a DC motor powered by the drivers can be varied.
The microcontroller controls the relay through a one transistor buffer, Q1.
An LED, D3, lights when the relay’s coil is energized. Diode D4 prevents a
damaging inductive voltage spike from occurring across the relay coil when the
transistor turns off.
Jumper
Channels
J7
B7, B6
J8
B5, B4
J9
A3, A2
J10
A1, A0
Enable
from PWM0.
channels
Enable
from PWM1.
channels
Channels
enabled.
always
Figure 1-4: Pulse Width Modulator Selection Jumpers
Output drivers U7 and U8 may be enabled under pulse width modulator control,
or may be always enabled. Jumpers J7 and J8 control IO11 DRIVER-B (U7).
Jumpers J9 and J10 control IO12 DRIVER-A (U8).
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2
The Serial Connection
The Experimenter may be connected to any type of computer equipped with
a serial port (RS-232C). On PCs serial ports are called COM ports. On Macs the
external modem port and printer port are both serial ports. Note that USB is not
compatible with RS-232C. If your computer does not come with an RS-232C
port you will need to add one to use the Experimenter. This chapter will help you
establish the serial link between your computer and the Experimenter. Connecting your Experimenter to a serial port on your computer is usually easy, but
occasionally there are complications.
The Physical Serial Connection
The Experimenter uses the same type of cable that would be used to connect
an external modem to your computer. The Experimenter is not a modem, of
course, but that type of cable is fairly common, so that is what we use.
The connector on the computer’s end of the cable is not so well standardized.
Some PCs use 9-pin D-sub connectors, some use 25 pins. Macs use an 8-pin Mini
Din connector. Standard PC and Mac cables are available from Fascinating
Electronics.
On a PC, you may have a choice of serial ports. The example programs in
this book were written in BASIC, and many versions of BASIC can only access
COM1 and COM2. If the your computer language is able to use other COM ports,
use the port you prefer.
On a Macintosh, use either the modem port (if your Mac does not have an
internal modem) or the printer port. Both of these are standard serial ports.
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Chapter 2: The Serial Connection
Some Nitty-Gritty Details
For those of you who like getting the nitty-gritty details, here is the technical
information. The Experimenter is configured as data communications equipment
ment, DCE. It expects to be sent transmitted data (TxD) on pin 2, and sends
out received data (RxD) on pin 3. It holds off sending data if data terminal
ready (DTR, pin 20) is false (or not connected). The Experimenter asserts data
set ready (DSR, pin 6), clear to send (CTS, pin 5), and carrier detect (CD,
pin 8) immediately when it is switched on.
Some computers and serial cables are manufactured with reduced signal
counts on the serial ports — as few as 3 wires (TxD, RxD, signal ground). If you
are using a three wire serial link you must add a wire from CTS (pin 5) to DTR
(pin 20) on the serial connector (J2). Otherwise the Experimenter believes that
your computer is sending an “I’m not ready” signal because it isn’t driving DTR
true. Sometimes serial cables and 9-pin to 25-pin adapters only connect the TxD,
RxD and signal ground pins. This can produce an “I’m not ready” problem on
both ends: both the Experimenter and the computer believing that the other
device is signaling that it is not ready to receive data. I have found tracing out
the adapter wiring with an ohm meter helps in identifying what is going wrong.
Direct Communication
The easiest way to begin using your Experimenter is with a communications
program like HyperTerminal. To use HyperTerminal create a New Connection
for the Experimenter. In the Connection Description menu name the connection
Experimenter and select an attractive icon. In the Connect To menu at the
Connect Using field select Direct To Com1 (or whichever com port you are
using). In the Com1 Properties menu set the baud rate to 9600 (make sure the
Experimenter is set to the same rate, see below), 8 data bits, no parity, 1 stop bit
and hardware flow control. You should now be able to type directly to your
Experimenter and see its responses in the Hyperterminal window. You can save
this connection and use it later (at the click of the new Experimenter.ht icon).
If you don’t have a communications program, Listing 2-1: ECHOEXP.BAS is a simple communications program written in BASIC, suitable for
use with the Experimenter. This particular version was written for a PC in
Microsoft’s QuickBASIC. You may need to modify this program to work on
other types of computers, and translate it for different dialects of BASIC. This
program will prompt you for which serial port to use. Other than that, ECHOEXP.BAS has all communications parameters preset for the Experimenter.
The Experimenter supports a variety of baud rates. The rate is set by J6.
Figure 2-1: Baud Rates gives the correspondence between baud rates and J6
jumper settings. The Experimenter checks the baud rate only once, at power-up.
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Chapter 2: The Serial Connection
If you change the setting while the Experimenter is running it will not notice the
change and will continue to use the old baud rate. So, if you change the setting
you must power-off the Experimenter. Be sure the Experimenter and your
communications program are using the same baud rate. The baud rate in ECHOEXP.BAS is preset for 9600 baud.
If everything is working, when you switch-on the Experimenter you will
see:
Experimenter Copyright 1991-93 Fascinating Electronics. Ver 1.0
Exp>
You may now start sending commands to the Experimenter. We will discuss
those commands in the following chapters.
At power-on, the Experimenter runs some diagnostic checks to make sure
it is working properly. If it finds any problems, it will report that to you. If you
did not get the above message, verify that the Experimenter’s power light (D1)
is on. If it is, try running the Experimenter in test mode. To select test mode,
install all three J6 jumpers. Cycle the power on the Experimenter, and if the
Experimenter is working properly the relay will repeatedly click on and off. If
it does then the problem is most likely not with the Experimenter, but with the
serial connection to your computer. Verify that you are using the correct serial
port, and the correct type of cable.
Test
300
1200
2400
4800
9600
19.2K
38.4K
Figure 2-1: Baud Rates
The Experimenter sets its baud rate from the jumper settings on J6. The value
is read only at power-on. The TEST setting (On-On-On) causes the relay to click
repeatedly. This is a simple diagnostic test to assure that the microcontroller is
working properly.
Listing 2-1: ECHO-EXP.BAS (next page)
This QuickBASIC program provides 9600 baud communication between a PC
and an Experimenter. Both source code and executable versions of this program
are available, along with the other programs in this book, on Application Disk #1
(SWP-AP1), available from Fascinating Electronics, Inc.
- 15 -
Chapter 2: The Serial Connection
' This program provides 9600 baud communications with an Experimenter.
backspace$ = CHR$(8)
linefeed$ = CHR$(10)
'Backspace is ASCII character 8.
'Linefeed is ASCII character 10.
' Clear the screen and select which COM port to use.
CLS
DO
INPUT "Which COM port will the Experimenter use (1 or 2)"; comPort%
PRINT
LOOP UNTIL comPort% = 1 OR comPort% = 2
LOCATE , , 0
'Turn off the cursor.
PRINT USING "Connecting to the Experimenter through COM#."; comPort%
PRINT
' Open the specified COM port as file #1.
ON ERROR GOTO ioError1
'On an error, give a helpful message.
IF comPort% = 1 then
OPEN "com1: 9600,n,8,1" FOR RANDOM AS #1
ELSE
OPEN "com2: 9600,n,8,1" FOR RANDOM AS #1
END IF
ON ERROR GOTO ioError2
'Ignore further errors.
CLS
PLAY "MB L32 C D E F G A B > C D E F G A B"
PRINT "Connected to the EXPERIMENTER!"
' Print message and activate cursor.
PRINT "------------------------------"
PRINT "Type Q to Quit and return to BASIC."
PRINT "Type ? for help with Experimenter commandss."
PRINT
LOCATE , , 1
'Activate the cursor.
' Check for keyboard input. Quit if the user types Q, otherwise send
the
' keystroke to the Experimenter. Backspaces erase the previous
character
' on the line. Linefeeds are ignored.
key$ = INKEY$
'Get any keystroke from the keyboard.
DO UNTIL UCASE$(key$) = "Q"
IF LEN(key$) > 0 THEN PRINT #1, key$;
IF NOT EOF(1) THEN
expKey$ = INPUT$(1, #1)
IF expKey$ = backspace$ then
LOCATE , POS(0) - 1
PRINT " ";
LOCATE , POS(0) -1
ELSEIF NOT expKey$ = linefeed$ THEN PRINT expKey$;
END IF
END IF
key$ = INKEY$
LOOP
CLS
END
' ******************** ERROR HANDLING ROUTINES *********************
' Error occurred while opening the COM port. Give a helpful message.
ioError1:
PLAY "MB L16 A B C"
PRINT "Be sure the Experimenter is powered-on, 9600 baud."
PRINT "Verify the Experimenter is connected to the correct COM
port."
PRINT
ON ERROR GOTO ioError2
RESUME
' Ignore all further errors.
ioError2:
RESUME
- 16 -
3
The
Firmware
The Experimenter has its own microprocessor running a built-in program.
Built-in software is called firmware. This firmware lets the Experimenter
perform many complex measurement and control activities without intervention
by your computer. Just send the Experimenter a command and off it goes.
When you request a measurement, or when you ask for the status of an
ongoing command, the Experimenter responds in plain ASCII text (no binary
numbers to convert). This makes it easy to communicate directly with the
Experimenter using a communication program (as suggested in the preceding
chapter), or to control the Experimenter through programs running on your
computer.
Help Features
The Experimenter has built-in help features. When you type a question mark
(?) at the Exp> prompt, the Experimenter responds with a table of the
commands and their parameters (see Figure 3-1
3-1). You can get help on individual
commands by giving the command name, followed by a question mark. All
Experimenter commands may be abbreviated by giving only the first letter of the
command.
Command Syntax
Version 1.0 firmware includes the commands A through I, with the
exception of B, which is reserved for a later firmware release. All other
commands will result in an error message. The Experimenter automatically
converts lowercase letters into uppercase, so you may enter either.
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Chapter 3: The Firmware
ANALOG channel
B-command reserved for later future use.
COUNTER/TIMER channel function wait
DIGITAL-I/O port out.1/mode dur.1 out.2 dur.2 out.3
ENABLE-PWM channel duty-cycle rate
FLIP-RELAY relay.number state
GENERAL-INFORMATION/CONTROL
selection
off/on
H-BRIDGE group direction duration speed type
INDIVIDUAL-OUTPUT channel state duration comp.duration cycles
**
To abbreviate, use only the first letter of the name
**
Figure 3-1: Help Text
The Experimenter prints this help text in response to a ?-command.
Each command may be followed by several parameters. Parameters are
integers, between 0 and a maximum of 65535. Values greater than 65535 will
result in an error message. Parameters may be separated from each other by just
about any other non-numeric character, but spaces are recommended. Do not put
commas in your numbers. That is, enter one-thousand as 1000 not as 1,000.
It is not always necessary to give every last parameter to a command every
time. For example, once given the speed and type parameters for an H-command,
the Experimenter remembers them for all subsequent H-commands for that
group. However, it is not possible to skip parameters. If you later want to issue
an H-command leaving all parameters the same except for type, you must again
provide all the parameters to the left of type.
Special Characters
Processing your command begins after you send a carriage return (enter).
The Experimenter stores the characters you send it in an input buffer. If you
reach the end of the input buffer before typing a carriage return, the Experimenter will not accept any further characters (and will not echo them). It will also
signal that this has happened by sending you a bell character (beep).
It is possible for the Experimenter to generate responses faster than they can
be communicated. The Experimenter maintains an output buffer for this text. If
the output buffer overflows, text will be lost. To inform you that this has
happened the Experimenter puts a pound sign (#) in the output buffer.
If you make a typing mistake, the backspace key will delete the previous
character from the Experimenter’s input buffer. It may not erase the character
from your computer screen, depending your communications program.
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Chapter 3: The Firmware
If you want to start over, the escape key causes the Experimenter to dump
the whole contents of the input buffer. This is also handy when initializing
computer control mode (described later), to get rid of any garbage characters that
may have come from noise on the communications line during power-on.
Xon/Xoff handshaking is supported by the Experimenter. In this type of
handshaking, your computer sends the Experimenter a control-S character
when it is running out of room in its input buffer. This causes the Experimenter
to stop sending characters. After your computer has digested the input, it sends
out a control-Q character causing the Experimenter to resume sending.
Software Controlled Communication
Software development for personal computers gets easier all the time. New
versions of old programming languages like BASIC have been given structured
programming constructs (no more line numbers!), high resolution graphics
support, and include nice editors and debugging capabilities. It is fun and
immensely satisfying to write a program that links physical world events to
graphics on your computer screen. It is also easy to do. Programming languages
have good support for the serial ports, so no special hardware driver is needed
for the Experimenter.
The Experimenter powers-on in manual communication mode
mode. This is for
the convenience of folks using communication programs as described in the
previous chapter. But the communication mode is easy to change. The GENERAL-INFORMATION/CONTROL command lets you switch the Experimenter to computer control mode
mode. Just send the command G 0 1. This does
several things:
1. It disables the echo of characters. Most communication programs expect
the system with which they connect to echo characters as they are typed.
Naturally, in computer control mode, echoing characters is unnecessary and
would just clutter up the Experimenter’s replies with the echoes of commands.
So, echo gets disabled.
2. It disables appending a linefeed after each carriage return. Again, most
communication programs expect a linefeed character after each carriage return.
But most programming languages looking for input from a serial port are only
expecting a carriage return. So, linefeed gets disabled.
3. It disables appending a 0 after each timer measurement. The timers in
the Experimenter measure in 10 microsecond steps. For example, a value of 56
corresponds to 560 microseconds. However, people think more clearly when we
stick with common units like milliseconds and microseconds, rather than
unusual units like 10’s of microseconds and quarters of fortnights. So, at power-
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Chapter 3: The Firmware
on the Experimenter defaults to adding a 0 to all timer measurements (except 0
itself, which is still 0 not 00). But your computer program can deal with any old
measurement choice—it’s all just numbers to your program. So, appending a 0
gets disabled.
There is one other thing your program should do before you get into the thick
of commands and responses. It should clear any pending characters out of its
input buffer. Otherwise, when your program goes to read its first response from
the Experimenter, the first thing it will get back is the Experimenter’s power-on
message. Which is very confusing if, for example, your program had just sent
a command and was expecting a number in response.
Computer Program Template
To give you some idea how to write a control program, Listing 3-2 provides
a template for you to use when writing programs that control the Experimenter.
Add your own statements in place of the comment block where it says “YOUR
CODE GOES HERE.” Notice how the program handles possible communications errors, initializes the communications port, and clears the input buffer. If
you get tired of the melody played every time the program successfully connects
with the Experimenter, just delete the PLAY statement after the CLS command.
As an example using this template, put the statements in Listing 3-1 in place
of the “YOUR CODE GOES HERE” block in Listing 3-2
3-2. This program will
scan the analog inputs as fast as your computer will go, presenting the measured
voltages on your computer. These values will be random voltages, unless you
connect something to the analog inputs. In the next chapter we will look at all
of the commands, and in the section on the ANALOG command we will discuss
providing voltages to the analog inputs.
' Print a header on the screen.
CLS
PRINT "Analog Voltage Scan, type Q to quit."
PRINT
PRINT "Channel
Millivolts"
PRINT "----------------"
DO
LOCATE 5, 1, 0
'Position for voltage readings.
FOR channel% = 0 TO 7
PRINT #1, "A"; channel% 'Request an analog measurement.
INPUT #1, value%
'Get measurement result.
PRINT USING "
#
####
"; channel%; value%
NEXT
LOOP UNTIL UCASE$(INKEY$) = "Q" 'Quit when 'Q' key is pressed.
Listing 3-1: ANALOG-8.BAS, Scans Analog Inputs
This program will scan the voltage measurement inputs (ANALOG 0:7) and
present the measurements on the display. Insert this code in place of the “YOUR
CODE GOES HERE” block in the TEMPLATE.BAS program.
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Chapter 3: The Firmware
' This is a template for you to use when writing computer programs
' for an Experimenter connected to COM1 or COM2 at 9600 baud.
escape% = 27
'<escape> is ASCII character 27.
' Clear the screen and select which COM port to use.
CLS
DO
INPUT "Which COM port will the Experimenter use (1 or 2)"; comPort%
PRINT
LOOP UNTIL comPort% = 1 OR comPort% = 2
LOCATE , , 0
'Turn off the cursor.
PRINT USING "Connecting to the Experimenter through COM#."; comPort%
PRINT
' Open the specified COM port as file #1.
ON ERROR GOTO ioError1
'On an error, give a helpful message.
IF comPort% = 1 then
OPEN "com1: 9600,n,8,1" FOR RANDOM AS #1
ELSE
OPEN "com2: 9600,n,8,1" FOR RANDOM AS #1
END IF
ON ERROR GOTO ioError2
'Ignore further errors.
CLS
PLAY "MB L32 C D E F G A B > C D E F G A B"
PRINT "Connected to the EXPERIMENTER!"
' Put the Experimenter in computer controlled mode, clear input buffer.
SLEEP 1
'Allow Experimenter time to power up.
PRINT #1, CHR$(escape%)
'Clear Experimenter of any characters.
SLEEP 1
‘Allow Experimenter time to execute
clear
PRINT #1, "G 0 1"
'Put in computer controlled mode.
SLEEP 1
'Allow time for transmit of command.
DO UNTIL EOF(1)
'Clear input buffer on your computer.
dummy$ = INPUT$(1, #1)
LOOP
' ******************************************************************
' *
The Experimenter is now ready. YOUR CODE GOES HERE!
*
' ******************************************************************
END
' ******************** ERROR HANDLING ROUTINES *********************
' Error occurred while opening the COM port. Give a helpful message.
ioError1:
PLAY "MB L16 A B C"
PRINT "Be sure the Experimenter is powered-on, 9600 baud."
PRINT "Verify the Experimenter is connected to the correct COM
port."
PRINT
ON ERROR GOTO ioError2
RESUME
' Ignore all further errors.
ioError2:
RESUME
Listing 3-2: TEMPLATE.BAS for Initializing the Experimenter
This listing is common to many programs that control the Experimenter. It sets
up communication between your computer and an Experimenter connected to
COM1 or COM2 at 9600 baud. It also initializes both your computer and the
Experimenter for computer controlled communications. By substituting in
chunks of code, such as Listing 3-1
3-1, your computer can command the Experimenter.
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4
C o m m a n d Tu t o r i a l
This chapter gives you a little background on each of the Experimenter
commands. The next chapter is a reference guide to the commands, giving detail
on each of the parameters. You may wish to refer to that chapter as you go
through this tutorial. While performing these exercises, you may communicate
Listing 2-1
with the Experimenter using HyperTerminal or ECHO-EXP.BAS (Listing
2-1).
ANALOG Voltage Measurement
Use the ANALOG command to measure and report the voltage on any of the
eight analog inputs (ANALOG 0:7). When you issue an A-command, the
Experimenter selects the channel you specified, makes the voltage measurement, and reports the value to you in millivolts.
The analog inputs are designed for monitoring relatively slowly varying
signals. If the slew rate on an analog input is greater than 10 volts/millisecond
the analog to digital converter may become confused and output an incorrect
value. This is usually the result of inadequate filtering or digital noise spikes
coupling into the analog signal. Isolating sensitive analog signals from digital
electronics should help. Adding a capacitor from the analog input to analog
ground (AG, part of IO6 ANALOG) may also prove helpful. A good value to try
is 0.1 µF.
A simple way of experimenting with this input is to connect up a potentiometer (pot) between the A+5 and AG pads. The value of the pot is not critical,
use any convenient value from 1 KΩ to 100 KΩ. Connect the wiper of the pot
to analog measurement input 0 (ANALOG 0). Put a 0.1 µF capacitor from the
wiper to the analog ground. See Figure 4-1
4-1.
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Chapter 4: Command Tutorial
Adjust the pot so that the wiper is about centered. Now give the command:
Exp> A 0
2500
The Experimenter measures the voltage on the wiper and should respond
with a value of about 2500 (millivolts). Now, adjust the pot so the wiper is all
the way to the A+5 end of the pot. Give the command:
Exp> A 0
5115
This time the Experimenter measured 5115 (millivolts). This is the maximum measurement voltage. Adjust the pot so that the wiper is all the way to the
AG end of the pot. Give the command:
Exp> A 0
0
Now the Experimenter has measured 0 (millivolts) on this input. This is the
minimum measurement voltage. When you connect analog sensors to these
inputs you must provide suitable scaling circuitry so that the voltage is within
the range from 0 to 5.12 volts. You will probably want to scale the input voltage
to take up most of this range for maximum resolution.
ANALOG
A+5
ANALOG 0
0.1 µF
Figure 4-1: Creating a Voltage with a Pot
A potentiometer provides a convenient way to
make an adjustable voltage for experimenting
with analog voltage measurement. The values
of the pot and cap are not critical—use any
convenient value from 1 KΩ to 100 KΩ, and
around 0.1 µF. By the way, this is how analog
joysticks work.
ANALOG
AG
B-COMMAND
This command is reserved for a future firmware release.
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Chapter 4: Command Tutorial
COUNTER/TIMER Pulse Counting / Time Measurement
The Experimenter has four counter/timer inputs (IO8 T-IN 0:3). These
inputs expect a logic level voltage swing, such as from a TTL or CMOS gate, and
can accept signals from mechanical devices like push-button switches.
Counter/timers can be used to count pulses or measure time intervals. To
explore some of these capabilities, you may wish to attach two push-button
switches to the counter/timer inputs as shown in Figure 4-2
4-2.
In the figure, switches are connected to inputs T-IN 0 and T-IN 1. When
pushed, the switches short the inputs to GND (logic low). Otherwise the pull-up
resistors bring the inputs up to the 5 volt logic supply (logic high). So, T-IN 0
and 1 should normally be high, should go low when you press the switch, then
should return high when you release the switch.
Lets try this. Issue the command:
Exp> C 0 1
0
This command tells the Experimenter to report the number of counts
accumulated on T IN 0, then to reset that counter, and set up the counter to count
rising edges (low-to-high transitions). Press and release the switch connected to
T IN 0 once. Now issue the command:
Exp> C 0 1
1
The counter should have counted to one. Did yours? You may have found
that the Experimenter counted some number greater than one. If it did, this is due
to a phenomenon called “contact bounce.” This happens because the electrical
contacts in mechanical switches (especially cheap mechanical switches) may
Logic +5
10 KΩ
Logic GND
- 24 -
Figure 4-2: Switches for Counter/Timers
Connect two normally open push-button
switches to the T IN 0 and T IN 1 inputs as
shown. The values of pull-up resistors
are not critical, but a value around
T IN 0
10 KΩ would be appropriate. Using
these switches you can investigate the
T IN 1
Experimenter’s ability to make time
measurements of real world events.
Chapter 4: Command Tutorial
not snap closed perfectly and stay together. Roughness in the surface of the
contacts, dirt, and the bouncing as the contacts strike each other may cause the
electrical signal produced by the switch to oscillate. The Experimenter is
sensitive to contact bounces lasting longer than a hundred microseconds or so.
One way to minimize contact bounce is to add a capacitor across the switch.
This damps out the oscillations, resulting in a gradual rise (and abrupt fall) in
voltage as the switch is opened and closed.
The first time we gave the command C 0 1, we started the counting. From
then on it would count each rising edge it saw on T-IN 0. Whenever the
Experimenter gets a count command, it reports the current value of that counter.
Since the counter was idle when we gave the first count command it reported 0.
When you pushed the button, one (or more) pulses were produced. The
Experimenter counted them. Then when you again issued the command C 0 1,
the Experimenter reported to you the number of pulses it had counted, reset the
counter to 0, and resumed looking for rising edges to count.
If you don’t want to reset the counter, you simply want to see what the
accumulated count is so far, then use the command C 0 0. If you want to stop
the counter after reporting a reading, you can use the command C 0 4. Any
pulses produced after this command will be ignored. You may wish to experiment with these commands.
Now lets look at a timer command. Issue the following command (but don’t
push either of the switches):
Exp> C 0 12
0
Counter/timer function 12 causes the Experimenter to measure the time
interval from a falling-edge on T-IN 0 to a falling-edge on T-IN 1. The
Experimenter waits for a couple of seconds for the first edge to occur. If it doesn't
see any edge it gives up waiting and returns a value of 0. This prevents the
Experimenter from “hanging” if no edge is present. You can program the length
of time for the Experimenter to wait, in 0.1 second increments. The command C 0 12 100 will cause the Experimenter to wait for 10 seconds before
giving up and reporting 0. If you give the command C 0 12 0 the Experimenter
will wait forever for that first edge. The power-up default is about 2 seconds.
Now let’s issue a command, followed by immediately pushing the switch
connected to T IN 0:
Exp> C 0 12
655350
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Chapter 4: Command Tutorial
About a half-second after the first switch was pressed, the Experimenter
printed the value 655350. The Experimenter started timing when the first switch
was pressed, measuring with a resolution of 10 microseconds. When the time
interval reached the maximum value of 655350 microseconds the counter was
stopped, and the Experimenter reported the value.
Lets try making a measurement. This will require quick reflexes. After you
issue the command C 0 12 100, you will have 10 seconds in which to press
the first button (going to T-IN 0). Then, as quickly as you can, press the second
button (going to T-IN 1). The Experimenter will measure and report the time
between button presses. The minimum measurement interval the Experimenter
can detect is under 250 microseconds.
DIGITAL I/O Input and Output through Digital Ports
The Experimenter provides 24 bits of digital I/O. Before using the digital I/O, you must select which ports you want to use as inputs and which ports
you want to use as outputs. Ports A and B are each eight bits wide (7:0), and port
C can be divided into two ports, each four bits wide (7:4, 3:0). Bit seven is the
most-significant bit (left-most), bit 0 is the least-significant (one’s) bit.
Let’s consider an example. Suppose you want port A and the high nibble of
port C to be outputs, port B and the low nibble of port C to be inputs. Look up
the DIGITAL I/O in the Command Reference chapter. In the table, we find that
the mode number for this configuration would be 131. So, in order to configure
the digital I/0 as desired, we must send the command D 3 131.
Now let’s suppose you want to send out the byte 10001000b to the A port for
25 seconds. The binary value 10001000b corresponds to 136 decimal. So, we
would send the command D 0 136 25000 0, meaning send to port A (number
0) the value 136 for a duration of 25000 milliseconds, then after that time expires
output the value 0.
If you wanted to check the progress of the timer, you could type:
Exp> D 0
136, 17531
This tells you that port A still has a value of 136, and that the duration
remaining for this output is 17,531 milliseconds. If you waited a while longer,
then typed:
Exp> D 0
0, 0
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Chapter 4: Command Tutorial
This shows that the timer has expired, and the value of the output port is
now 0. The digital I/O command will let you sequence up to three bytes on each
port, with durations of from 1 to 65535 milliseconds between them. This is useful
for creating control signals and strobes. With additional buffering, these outputs
can be used to drive motors, solenoids, pneumatic and hydraulic valves, and
other devices.
Now let’s look at using these ports as inputs. Suppose you want to read port
B, which we had set up to be an input port. The command D 1 would read the
value of port B, and would respond with two numbers as above. The first number
is the value read from the port. The second number is always 0 in Version 1.0
firmware.
Input ports are useful for sensing switches and monitoring digital signals.
Suppose you were building a sophisticated burglar alarm for your home. You
could install magnetic switches in the doors and windows that trigger when
opened. In the figure below, several switches are used on windows in the family
room, one is used on the front door. When the door or any of the three windows
are opened, the input to the Experimenter goes high. Your computer could then
take appropriate action. Using the relay on the Experimenter, your computer
could switch-on a loud alarm horn, or switch-on a tape recording of a vicious
barking dog.
+5 V Logic Supply
Magnet
Magnet
Magnet
DIGITAL-I/O B0
Window 1
Window 2
Window 3
Logic GND
Magnet
DIGITAL-I/O B1
Front Door
Logic GND
Figure 4-3: Magnetic Switches for a Burglar Alarm
These magnetic switches are closed when a magnet is near them, and open when
the magnet moves away. The pull-up resistors cause the digital I/O lines to go
to logic 1 when the switches open. Resistor values are not critical, but a value
in the 1 KΩ to 10 KΩ range would be appropriate.
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Chapter 4: Command Tutorial
ENABLE-PWM Enable Drivers with PWM
Pulse width modulation is a technique for achieving analog-like voltage
control using only digital logic. The PWM controls the proportion of time that
an output is driven. When the output is driven a large proportion of the time, the
effect is as if a large analog voltage is present. When the output is driven a small
proportion of the time, the effect is as if a small analog voltage is present.
There are two pulse width modulators on the Experimenter (0 and 1). Each
is independently controlled. You can control both the duty-cycle and the rate.
The duty-cycle is the proportion of enabled to disabled time. The rate determines
how many cycles are produced each second. Figure 4-4 shows the enable
waveform available at the PWM outputs (IO9 PWM 0:1).
The power-on defaults set the PWM outputs high 100% of the time (dutycycle = 255), and run at the maximum rate of 14,456 pulses per second—a period
of about 0.07 milliseconds per pulse (rate = 0). Table 5-1 in the Command
Reference chapter lists all of the rate values and their corresponding frequency
and period.
Jumpers J7 through J10 are provided so that the eight driver outputs may be
selected in pairs to be enabled by PWM0 or PWM1. If no jumper is present the
pair is always enabled. J10 controls 0/1, J9 2/3, J8 4/5, J7 6/7.
Pulse width modulation can be used to control the speed of DC motors and
the torque of stepping motors. Since the topic of motor control is fairly involved,
Chapter 6 is devoted solely to controlling motors.
You can turn a PWM output into an analog voltage by running it through a
low-pass filter. A series resistor and a capacitor to ground will usually work just
fine.
duty-cycle
rate
Figure 4-4: Pulse Width Modulation (IO9 PWM 0:1)
The Experimenter has two PWM outputs. They may also be used to enable the
high current driver outputs in pairs. Drivers are enabled when their enable
inputs are high (logic 1).
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Chapter 4: Command Tutorial
FLIP-RELAY Switches Relay On and Off
The Experimenter has one relay for controlling high-power devices. The
command F 0 1 turns the relay on. The first parameter is the relay number.
There is only one relay on this version of the Experimenter, but the relay number
was included for upward compatibility with possible future versions. The second
parameter controls the state of the relay. The command F 0 0 turns the relay
off. The command F 0 2 toggles the state of the relay. If you would like to
know the current state of the relay, the command F 0 reports the current state.
There are three pads adjacent to the relay. They are marked IO2 NC,
IO3 NO, and IO4 COM. When the relay is off, the COM (Common) terminal
connects to the NC (Normally Closed) terminal. When the relay is active, the
COM terminal disconnects from the NC terminal and connects to the NO
(Normally Open) terminal. An LED, D3, lights when the relay is active.
GENERAL-INFORMATION/CONTROL
This command lets you adjust the way that the Experimenter communicates
over the serial port. In Chapter 3, in the section on Software Controlled
Communication, we saw how to use the GENERAL-INFORMATION/CONTROL command to disable some of the extra characters the Experimenter
normally sends. The functions enabling/disabling the echo of characters,
appending a linefeed after each carriage return, and appending a “0” after each
timer measurement can each be independently controlled. These features may
be useful to adapt the Experimenter’s style to your communication program.
For example, some terminal emulation programs may automatically append
a linefeed to each carriage return received. Since the Experimenter normally
defaults to send a linefeed, this would cause the output on your screen to appear
double-spaced. To correct this, the command G 2 0 would turn off the
appending of linefeeds but leave the Experimenter in manual controlled mode.
The command G 2 1 would turn them back on.
If the Experimenter is running in computer controlled mode (not echoing
characters, etc.), and you wish to return it to manual control send the single-letter
command G. This will restore all of the default communications features and will
print the power-on message.
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Chapter 4: Command Tutorial
H-BRIDGE Control Motors
Controlling motors, especially stepping motors, is one of the most fun ways
to use the Experimenter because it gives your computer a way to actually
manipulate objects in the physical world. To help you with this Chapter 6 is
devoted to DC and stepping motors. This section will explain how to use the
H-BRIDGE command itself.
The H-command has five parameters. The first parameter, group, tells the
Experimenter which drivers, and thus which motor, you wish to control with this
command. DC motors each require only two drivers. The Experimenter can
support up to four DC motors, so there are four groups (numbered 0 to 3).
Driver A (U8) supports the even-numbered motors (0, 2). Driver B (U7) supports
the odd-numbered motors (1, 3).
Stepping motors require four drivers each, so there are only two groups
(0:1). Again, driver A supports the even-numbered motor (0), driver B the oddnumbered motor (1).
The Experimenter can also support one stepping motor and two DC motors.
If the stepping motor is on driver A, it is number 0, and the DC motors on driver
B are numbers 1 and 3. If the stepping motor is on driver B, it is number 1, and
the DC motors on driver A are numbers 0 and 2.
The second parameter, direction, controls which direction the motor is to
rotate. The value 1 causes the motor to go forward, 2 to go reverse, and the values
0 and 3 cause the motor to stop. If the motor is a stepping motor, stop-0 causes
the motor to stop with the coils energized, and stop-3 causes the motor to stop
with the coils off.
The duration parameter tells the Experimenter how long to run the motor.
For a DC motor, the duration value is interpreted as milliseconds. For a stepping
motor, the duration is interpreted as steps. Thus, for a DC motor, a duration of
2000 means 2 seconds, but for a stepping motor it means 2000 steps. A duration
of 0 means to run the motor until a stop instruction is sent.
The speed parameter controls two different things, depending on whether
the command is for a stepping motor or a DC motor. If for a DC motor, the speed
parameter adjusts the duty-cycle of one PWM. Since there are only two PWM’s
and there can be four DC motors changing the speed of one DC motor will also
change the speed of another DC motor on thatPWM. Note that a larger speed
value makes a DC motor run faster, because the duty-cycle is increased.
When controlling a stepping motor, the speed parameter is the time the
motor spends making each step (in milliseconds). For a stepping motor, the
larger the speed value the slower the motor runs. The total time it takes to make
a particular movement is the product of the duration times the speed (in mS).
- 30 -
Chapter 4: Command Tutorial
The type parameter tells the Experimenter exactly what type of motor you
are using, and the drive pattern to use with it. DC motors are either type 0 or 1,
depending on which way the motor leads are connected. Table 5-2 in the next
chapter gives the type values for the various kinds of stepping motors. Chapter
6 will explain enough about stepping motors that this table should make sense.
The Experimenter remembers the speed and type parameters, and these
parameters need not be provided again unless you want to change them.
There is also a way to determine the progress of an ongoing H-command.
If sent an H-command with just the group parameter given, the Experimenter
reports the remaining duration for that group.
INDIVIDUAL-OUTPUT Controls Driver Outputs Individually
Each of the Experimenter’s eight driver outputs can be individually
controlled with the INDIVIDUAL-OUTPUT command, including timing and
number of pulses. The command has five parameters.
The first parameter, channel, selects which output driver. Channels are
numbered from 0 to 7, corresponding to DRIVER-A 0:3 and DRIVER-B 4:7.
The next parameter, state, selects the output voltage. A value of 0 outputs
a low voltage, 1 outputs a high voltage. A value of 2 causes the channel to toggle.
The duration parameter sets how long (in milliseconds) the channel will
remain in the specified state. When duration has expired, the output will toggle
and remain in the new state as long as specified by the complement.duration
parameter (also in milliseconds).
The cycles parameter limits the number of repeats before stopping. If the
complement.duration is 0, the output will remain in the initial state for the entire
interval of cycles * duration. A value of 0 puts no limit on the number of cycles.
To determine the progress of an ongoing I-command, give the command
with only the channel parameter. The Experimenter will report three numbers
(separated by commas and spaces): the value of the current state, the duration
remaining for that state, and the number of cycles remaining.
As an example, the command I 5 1 100 200 250 produces a pulse
on DRIVER-B 5 that is high (1) for 100 milliseconds, low for 200 milliseconds,
and repeats to produce 250 pulses. While this pulse stream is running, if you issue
the command I 5 the Experimenter will report three numbers. For example,
the Experimenter may report 1, 25, 175 meaning the output state is currently
high, that it will remain in that state for 25 more milliseconds, and that there are
175 cycles remaining to be produced.
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5
Command Reference
Experimenter firmware Version 1.0 provides eight commands, with from
one to six parameters each. Each section of this chapter describes one of these
commands, its parameters, responses (if any), and any special considerations for
use.
If you have suggestions for additional commands, changes to these commands, or any other ideas for improving the Experimenter, please let us know.
Your feedback is very important to us.
ANALOG Voltage Measurement
Reports the voltage on the specified analog input channel (IO6 ANALOG 0:7).
A channel
channel analog input channel number
none channel 0 assumed
0 to 7 available channel selections
Notes:
1. Measurements have 5 mV resolution over the range from 0 to 5.115 volts.
2. Values are reported as integers from 0 to 5115, in multiples of 5.
3. Slew rates exceeding 10 volts/millisecond, or voltages above 5.12 volts or
below ground on any analog input may result in erroneous measurements.
B-COMMAND
This command is reserved for a future firmware release.
- 32 -
Chapter 5: Command Reference
COUNTER/TIMER Pulse Counting / Time Measurement
Counts pulses and measures time intervals on the specified counter/timer input
channel(s) (IO8 T-IN 0:3).
C channel function wait
channel counter/timer input channel
none channel 0 assumed
0 to 3 available channel selections
function counter/timer measurement function
Counter Measurements:
none or 0 report the current count (counter unchanged)
1 report count, restart counter, count on rising edge
2 report count, restart counter, count on falling edge
3 report count, restart counter, count on both edges
4 report count, reset counter, counting stopped
Single Channel Timer Measurements:
5 measure and report positive-going pulse duration
6 measure and report negative-going pulse duration
7 measure and report rising-edge to rising-edge period
8 measure and report falling-edge to falling-edge period
Two Channel Timer Measurements:
9 measure and report rising-edge to falling-edge time
10 measure and report falling-edge to rising-edge time
11 measure and report rising-edge to rising-edge time
12 measure and report falling-edge to falling-edge time
wait timer maximum waiting period for the start of a measurement
none use previous (or default) value
0 unlimited wait
1 to 255 waiting period, in 100 millisecond steps
Notes:
1. Maximum count rate is well over 1 kilohertz. Maximum count value is 65535.
Further pulses beyond 65535 are ignored.
2. Timer measurements may range from about 250 microseconds to 655350
microseconds, with 10 microsecond resolution. The time is presented either
in microseconds or in tens-of-microseconds (refer to Chapter 3, Software
Controlled Communication for details of 0-append to timer measurements).
3. If the first edge defining a timer measurement does not occur within the
specified wait time, a value of 0 will be returned, and the measurement
terminated. This is to avoid “hanging” the Experimenter in the event that no
signal is present.
- 33 -
Chapter 5: Command Reference
DIGITAL I/O Input and Output Digital Ports
24 bits of digital input and output (IO13 DIGITAL-I/O A 7:0, B 7:0, C 7:0).
D 3 mode
(To configure port I/O)
mode ports A, B, and C are set to inputs and outputs as follows:
mode
A7:0
C7:4
B7:0
C3:0
128
out
out
out
out
129
out
out
out
in
130
out
out
in
out
131
out
out
in
in
136
out
in
out
out
137
out
in
out
in
138
out
in
in
out
139
out
in
in
in
144
in
out
out
out
145
in
out
out
in
146
in
out
in
out
147
in
out
in
in
152
in
in
out
out
153
in
in
out
in
154
in
in
in
out
155
in
in
in
in
D port
(For reading inputs or checking status of outputs)
port selected input/output port
none or 0 port A is selected
1 port B is selected
2 port C is selected
If the selected port is an output:
Reports the current value and the remaining duration
for the output, separated by a comma and a space.
If the selected port is an input:
Reads and reports the current input value and the
number 0, separated by a comma and a space.
D port output.1 duration.1 output.2 duration.2 output.3 (For outputs)
port selected input/output port
none or 0 port A is selected
1 port B is selected
2 port C is selected
output.1 initial output value
none port is read: value and duration remaining is reported
0 to 255 value written to port outputs
- 34 -
Chapter 5: Command Reference
duration.1 time duration output.1 is present on port outputs
none or 0 duration is unlimited
1 to 65535 duration in milliseconds
output.2 next output value (after duration.1 is over)
none or 0 0 is written to port outputs
1 to 255 value written to port outputs
duration.2 time duration output.2 is present on port outputs
as above for duration.1
output.3 final output value
as above for output.2
Note:
1. The D 3 mode command is required to initialize ports for output. This also
resets all outputs to 0.
ENABLE-PWM Enable Drivers with PWM
Controls the duty-cycle and period of the pulse width modulation outputs
(IO9 PWM 0:1). These can enable the driver chips, controlling output power.
E channel duty-cycle rate
channel counter/timer input channel
none or 0 PWM 0 is selected
1 PWM 1 is selected
duty-cycle counter/timer input channel
none report current pulse width setting
0 always off (low)
1 to 254 variable pulse width
255 always on (high)
rate controls the pulse rate
none use previously assigned value, default 0
0 to 255 0 is fastest, 255 is slowest
Notes:
1. The PWM pulse frequency can be calculated from the equation:
Frequency = 7372800/(510*(1+rate)) cycles per second.
2. The PWM pulse period can be calculated from the equation:
Period = (510*(1+rate))/7372.8 milliseconds.
3. Table 5-1, on the next page, gives the frequency (in cycles per second) and
period (in milliseconds) for all values of rate.
- 35 -
Chapter 5: Command Reference
Table 5-1: Pulse Width Modulator Rate, Frequency, and Period
The rate parameter to the E-command allows you to control the pulse rate of the
pulse width modulator. This table gives you the frequency (in cycles per second)
and the period (in milliseconds) for each rate setting.
Rate Freq Period
0 14,456 0.07
1 7,228 0.14
2 4,819 0.21
3 3,614 0.28
4 2,891 0.35
5 2,409 0.42
6 2,065 0.48
7 1,807 0.55
8 1,606 0.62
9 1,446 0.69
10 1,314 0.76
11 1,205 0.83
12 1,112 0.90
13 1,033 0.97
14 964 1.04
15 904 1.11
16 850 1.18
17 803 1.25
18 761 1.31
19 723 1.38
20 688 1.45
21 657 1.52
22 629 1.59
23 602 1.66
24 578 1.73
25 556 1.80
26 535 1.87
27 516 1.94
28 498 2.01
29 482 2.08
30 466 2.14
31 452 2.21
32 438 2.28
33 425 2.35
34 413 2.42
35 402 2.49
36 391 2.56
37 380 2.63
38 371 2.70
39 361 2.77
40 353 2.84
41 344 2.91
42 336 2.97
43 329 3.04
44 321 3.11
45 314 3.18
46 308 3.25
47 301 3.32
48 295 3.39
49 289 3.46
50 283 3.53
- 36 -
Rate Freq Period
Rate Freq Period
Rate Freq Period
Rate Freq Period
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
278
273
268
263
258
254
249
245
241
237
233
229
226
222
219
216
213
210
207
204
201
198
195
193
190
188
185
183
181
178
176
174
172
170
168
166
164
162
161
159
157
155
154
152
151
149
148
146
145
143
142
3.60
3.67
3.74
3.80
3.87
3.94
4.01
4.08
4.15
4.22
4.29
4.36
4.43
4.50
4.57
4.63
4.70
4.77
4.84
4.91
4.98
5.05
5.12
5.19
5.26
5.33
5.40
5.46
5.53
5.60
5.67
5.74
5.81
5.88
5.95
6.02
6.09
6.16
6.23
6.29
6.36
6.43
6.50
6.57
6.64
6.71
6.78
6.85
6.92
6.99
7.06
140
139
138
136
135
134
133
131
130
129
128
127
126
125
124
123
121
120
119
118
118
117
116
115
114
113
112
111
110
110
109
108
107
106
106
105
104
103
103
102
101
100
99.7
99.0
98.3
97.7
97.0
96.4
95.7
95.1
94.5
7.12
7.19
7.26
7.33
7.40
7.47
7.54
7.61
7.68
7.75
7.82
7.89
7.95
8.02
8.09
8.16
8.23
8.30
8.37
8.44
8.51
8.58
8.65
8.72
8.78
8.85
8.92
8.99
9.06
9.13
9.20
9.27
9.34
9.41
9.48
9.55
9.62
9.68
9.75
9.82
9.89
9.96
10.03
10.10
10.17
10.24
10.31
10.38
10.45
10.51
10.58
93.9
93.3
92.7
92.1
91.5
90.9
90.4
89.8
89.2
88.7
88.1
87.6
87.1
86.6
86.1
85.5
85.0
84.5
84.0
83.6
83.1
82.6
82.1
81.7
81.2
80.8
80.3
79.9
79.4
79.0
78.6
78.1
77.7
77.3
76.9
76.5
76.1
75.7
75.3
74.9
74.5
74.1
73.8
73.4
73.0
72.6
72.3
71.9
71.6
71.2
70.9
10.65
10.72
10.79
10.86
10.93
11.00
11.07
11.14
11.21
11.28
11.34
11.41
11.48
11.55
11.62
11.69
11.76
11.83
11.90
11.97
12.04
12.11
12.17
12.24
12.31
12.38
12.45
12.52
12.59
12.66
12.73
12.80
12.87
12.94
13.00
13.07
13.14
13.21
13.28
13.35
13.42
13.49
13.56
13.63
13.70
13.77
13.83
13.90
13.97
14.04
14.11
70.5
70.2
69.8
69.5
69.2
68.8
68.5
68.2
67.9
67.6
67.2
66.9
66.6
66.3
66.0
65.7
65.4
65.1
64.8
64.5
64.3
64.0
63.7
63.4
63.1
62.9
62.6
62.3
62.0
61.8
61.5
61.3
61.0
60.7
60.5
60.2
60.0
59.7
59.5
59.2
59.0
58.8
58.5
58.3
58.1
57.8
57.6
57.4
57.1
56.9
56.7
56.5
14.18
14.25
14.32
14.39
14.46
14.53
14.60
14.66
14.73
14.80
14.87
14.94
15.01
15.08
15.15
15.22
15.29
15.36
15.43
15.49
15.56
15.63
15.70
15.77
15.84
15.91
15.98
16.05
16.12
16.19
16.26
16.32
16.39
16.46
16.53
16.60
16.67
16.74
16.81
16.88
16.95
17.02
17.09
17.15
17.22
17.29
17.36
17.43
17.50
17.57
17.64
17.71
Chapter 5: Command Reference
FLIP-RELAY Switches Relay On and Off
Sets, resets, or toggles the single-pole double-throw relay, or reports its state.
F relay.number state
relay.number the relay number
any the relay number is ignored
state reads or sets the relay's state
none report the relay's current state
0 relay coil off
1 relay coil on
2 toggle the relay’s state
Notes:
1. The parameter relay.number is included for compatibility with possible
future versions of the Experimenter having more than one relay. Firmware
Version 1.0 ignores the value of relay.number.
2. When the relay coil is off, the IO2 NC (Normally Closed) contact is connected
to the IO4 COM (Common) contact—when on, the IO3 NO (Normally Open)
contact is connected to COM.
GENERAL-INFORMATION/CONTROL
General information about the Experimenter is reported, and special functions
are controlled.
G select off/on
select selects the information or control function
none or 0 manual (default) / computer control mode (when on)
1 echo typing
2 append a linefeed after each carriage-return
3 append a 0 to all non-zero timer measurements
off/on disables or enables the selection
none or 0 turn the selection off
1 turn the selection on
Notes:
1. Manual mode defaults to enable selections 1, 2 and 3; computer control mode
disables them.
Exp>
2. The echo typing selection also enables the prompt message (Exp>
Exp>).
- 37 -
Centerfold:
Experimenter 2Schematic
1
3
4
A[0..15]
D[0..7]
A
C15
33p
C16
33p
U6
S80C552
Y1
7.3728/11.0592
35
34
RESET
VCC
OFF
J11
WATCHDOG
ON
15
RESET
EW
EA
60
58
C25
0.1
AG
A+5
7
IO6
ANALOG 6
5
4
3
2
1
0
C
IO9
PWM
0
1
INT
IO7
D
PWM0
PWM1
J6
BAUDRATE
1
3
5
29
28
27
P2
RS-232C
26
E
F
G
PSEN
21
13
25
12
24
11
23
10
22
9
21
8
20
7
19
6
18
5
17
4
16
3
15
2
14
1
P3.6/WR
P3.7/RD
C4
C5
C6
C7
0
1n
1n
1n
1n
VCC
R5 1K
Q1
2N3906
D3 RELAY R7 220
1
3
C11
4.7
4
5
8
7
14
13
A8
A9
A10
A11
A12
A13
A14
A15
3
4
7
8
13
14
17
18
1
11
22
23
48
AS1
AS2
47
PSEN
30
WR
31
RD
7
8
9
10
11
12
13
14
T0
T1
T2
T3
T4
T5
T6
T7
IO10
T-OUT
T0
0
T1
1
T2
2
T3
3
T4
4
T5
5
T6
6
T7
7
24
25
20
NC
IO4
COM
IO3
NO
RL1
RELAY
C1+
C1-
VCC
V+
C2+
C2-
VGND
R2IN R2OUT
T2OUT
T2IN
T1OUT
T1IN
R1IN R1OUT
1D
2D
3D
4D
5D
6D
7D
8D
1Q
2Q
3Q
4Q
5Q
6Q
7Q
8Q
16
2
VCC
2
5
6
9
12
15
16
19
T0
U8
SN
10
T1
15
J10 0
EN01
1
9
PWM0
PWM1
T2
U8
SN
2
T3
7
0
J9
EN23
1
1
PWM0
PWM1
T4
U7
SN
10
T5
15
9
PWM0
PWM1
C10
4.7
2
1
6
15
IO5
BOOST
T6
U7
SN
2
+10
-10
T7
7
C12
4.7
9
10
11
12
A0
A1
A2
A3
A4
A5
A6
A7
OC
G
0
J8
EN45
1
0
J7
EN67
1
TP8
+5
TP9
+5
1
PWM0
PWM1
TP10 TP11 TP12 TP
+5
+5
+5
+5
VCC
C3
0.1
TP4
DSR
39
40
41
42
43
44
45
46
D0
D1
D2
D3
D4
D5
D6
D7
D4 1N4001
C9
4.7
TP3
RXD
D0
D1
D2
D3
D4
D5
D6
D7
IO2
U5
ST202ECN
TP2
TXD
57
56
55
54
53
52
51
50
T[0..7]
P4.0/CMSR0
PWM0
P4.1/CMSR1
PWM1
P4.2/CMSR2
P4.3/CMSR3
P3.2/INT0 P4.4/CMSR4
P4.5/CMSR5
P4.6/CMT0
P3.5
P4.7/CMT1
P3.4
P3.3
P3.0/RXD
P3.1/TXD
P1.5
P1.4/DTR
26
2
4
6
P1.6/SCL
P1.7/SDA
ALE
P1.0/CT0
P1.1/CT1
P1.2/CT2
P1.3/CT3
4
5
1
2
A8
A9
A10
A11
A12
A13
A14
A15
AVDD
AVREF+
P5.7/ADC7
P5.6/ADC6
P5.5/ADC5
P5.4/ADC4
P5.3/ADC3
P5.2/ADC2
P5.1/ADC1
P5.0/ADC0
STADC
16
17
18
19
0
1
2
3
IO8
T-IN
AVSS
AVREF-
61
59
62
63
64
65
66
67
68
1
3
A+5
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
XTAL2
6
49
B
U2
74LS373
XTAL1
C19
0.1
C8
0.1
C14
0.1
C17
0.1
C18
0.1
TP5
DTR
- 38 -
10
1
6
2
7
3
8
4
9
5
X2
DB25M
0
26
1
14
2
15
3
16
4
17
5
18
6
19
7
20
8
21
9
22
10
23
11
24
12
25
13
H
0
TP1 TP6 TP18 TP19 TP20 TP21 TP22 TP
GND GND GND GND GND GND GND GN
X3
DB9
Centerfold:
Experimenter8Schematic
7
U4
2716-27512
P27
J3 1
P1 2
3
P1
J4 1
P23 2
3
P23
J5 1
P26 2
3
P26
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
P23
A12
P26
P27
P1
A14
A15
A11
A13
8
11
10
9
8
7
6
5
4
3
25
24
21
23
2
26
27
1
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
20
22
O0
O1
O2
O3
O4
O5
O6
O7
U3
62C1024
11
12
13
15
16
17
18
19
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
AS1
AS2
CE
OE
14
VCC
8A
N754410
RD
GND
0
1
2
3
+A
SW-PWR
SW-PWR
R9 10K
8
3
22
30
24
29
A15
IO12
PSEN
DRIVER-A
R3
1K
VCC
WR
VCC
D0
D1
D2
D3
D4
D5
D6
D7
R2
1K
AS2
D2
POWER
VCC
R1
220
34
33
32
31
30
29
28
27
A0
A1
A15
9
8
R8 10K
6
5
36
RD
LM2940
VIN
VCC
R6 10K
WR
3
OUT
RESET
C2
330
2
GND
4
5
6
7
+B
SW-PWR
SW-PWR
14
7A
N754410
U1
1
GND
IO11
DRIVER-B
8
11
IO1
BACKUP
D1
1N4001
C21
0.1
D0
D1
D2
D3
D4
D5
D6
D7
PA0
PA1
PA2
PA3
PA4
PA5
PA6
PA7
A0
A1
PB0
PB1
PB2
CS
PB3
RD
PB4
WR PB5
PB6
PB7
RESET
PC0
PC1
PC2
PC3
PC4
PC5
PC6
PC7
4
3
2
1
40
39
38
37
IO13A
0
1
2
3
4
5
6
7
18
19
20
21
22
23
24
25
IO13B
0
1
2
3
4
5
6
7
14
15
16
17
13
12
11
10
IO13C
0
1
2
3
4
5
6
7
VIN
ADJ
OFF
LM2941
OUT
5
J12
1
2
3
R12
200
CCW
TP7
5.12V
R10
6.04K
C22
330
C24
0.1
F1
FOOT
10
1
6
2
7
3
8
4
9
5
0
W
R11
2.00K
CW
P23 TP24 TP25 TP26 TP17 TP27
ND GND GND GND GND GND
9F
CE1
CE2
OE
WE
3
C1
0.47
J1
POLARITY
P13 TP14 TP15 TP16
5
+5
+5
+5
C20
0.1
Unless otherwise
indicated, resistor
values are in ohms,
capacitor values are
in microfarads.
GND
4
1
2
2
4
C23
0.1
D0
D1
D2
D3
D4
D5
D6
D7
Note:
U10
1
3
R4 10K
13
14
15
17
18
19
20
21
VCC
A+5
6
P1
POWER
I/O0
I/O1
I/O2
I/O3
I/O4
I/O5
I/O6
I/O7
S1
POWER
+BAT
-BAT
VCC
35
C13
1u
VCC
8
3
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A16
U9
82C55A
AS1
6
7B
N754410
12
11
10
9
8
7
6
5
27
26
23
25
4
28
3
31
2
DIGITAL-I/O
8B
N754410
J2 1
P27 2
3
DIGITAL-I/O
VCC
0
1
2
3
4
5
6
7
DIGITAL-I/O
6
ANLGSEL
5
F2
FOOT
F3
FOOT
F4
FOOT
F5
FOOT
F6
FOOT
F7
F8
DTRMT DTRMT
X4
DB9M
- 39 -
Chapter 5: Command Reference
H-BRIDGE Control Motors
Configures the drivers as an H-Bridge to control DC or stepping motors.
H group direction duration speed type
group selects groups of driver outputs
For DC Motors:
0 DRIVER-A 0 and 1; controls PWM 0
1 DRIVER-B 4 and 5; controls PWM 1
2 DRIVER-A 2 and 3; controls PWM 0
3 DRIVER-B 6 and 7; controls PWM 1
For Stepping Motors:
0 DRIVER A 0, 1, 2, 3
1 DRIVER B 4, 5, 6, 7
direction motor direction control
none report remaining duration
0 stop (for stepper: coils on)
1 forward
2 reverse
3 stop (for stepper: coils off)
duration how long to drive the motor, then return to stop (0)
none or 0 drive duration unlimited
1 to 65535 for DC motors: duration in milliseconds
for stepping motors: duration in steps
speed PWM control for DC motors, step duration for stepping motors
For DC Motors:
none or 0 PWM settings are not changed
1 to 255 PWM duty-cycle set as in the E-command
For Stepping Motors:
none or 0 rate is not changed (default 255 milliseconds/step)
1 to 65535 step duration in milliseconds/step
type selects type of motor and driver configuration
none type of motor is not changed
For DC Motors:
0 positive polarity (default)
1 negative polarity
For Stepping Motors:
2 to 11 see Table 5-2 on the next page
- 40 -
Chapter 5: Command Reference
Table 5-2: Stepping Motor Configuration Types
The Experimenter can control all common types of stepping motors. The type
parameter tells the Experimenter how to drive the particular motor you are
using. The chapter DC and Stepping Motors tells you how to recognize the
various types of stepping motors. Then, using this table, you can select the
correct type parameter for the motor you are using.
Type
2
3
Coil Configuration
3-coil unipolar
3-coil unipolar
Common
- supply
+ supply
Drive Pattern
1-phase
1-phase
4
5
3-coil unipolar
3-coil unipolar
- supply
+ supply
half-step
half-step
6
7
4-coil unipolar
4-coil unipolar
- supply
+ supply
1-phase
1-phase
8
4-coil
2-coil
4-coil
2-coil
unipolar or
bipolar
unipolar or
bipolar
- supply
none
+ supply
none
2-phase
2-phase
2-phase
2-phase
4-coil
2-coil
4-coil
2-coil
unipolar or
bipolar
unipolar or
bipolar
- supply
none
+ supply
none
half-step
half-step
half-step
half-step
9
10
11
Notes:
1. When a new stepper command is issued for a group with an ongoing stepper
command, if the current step is longer than 50 milliseconds it is shortened to
50 milliseconds. Then, upon the completion of the current step, the new
command begins.
2. If only the group parameter is given, the Experimenter reports the remaining
duration for any ongoing stepper command on that group.
3. Since both the H-command and I-command share the driver outputs, issuing
an H-command for a group that includes a channel in use by an I-command
will cause that I-command to terminate.
- 41 -
Chapter 5: Command Reference
INDIVIDUAL-OUTPUT Controls Driver Outputs Individually
Controls state and timing for eight driver outputs individually (DRIVER-A 0:3,
DRIVER-B 4:7).
I channel state duration complement.duration cycles
channel selected driver
none channel 0 assumed
0 to 7 available channel selections
state initial output state
none report state, remaining time in state, remaining cycles
0 initial state is low
1 initial state is high
2 initial state is the complement of the current state
duration time duration for the initial state
none or 0 duration is unlimited
1 to 255 duration of initial state, in milliseconds
comp.dur duration for the complement state
none or 0 0 time between initial states
1 to 255 duration of complement state, in milliseconds
cycles limit on the number of cycles to be repeated
none or 0 cycle without limit
1 to 255 perform this number of cycles, then stop
Notes:
1. To get longer durations for a single pulse, set complement.duration to 0. The
duration of the single pulse produced will be duration * cycles (milliseconds).
2. If only the channel parameter is given, the Experimenter reports the current
state, the duration remaining for that state, and the number of cycles
remaining for that channel.
3. Since both the H-command and I-command share the driver outputs, issuing
an I-command for a channel that is part of a group in use by an H-command
will cause that H-command to terminate.
- 42 -
6
DC and Stepping Motors
This chapter is a tutorial on DC and stepping motors. A stepping motor is
a remarkable device, much different from ordinary DC motors. Ordinary DC
motors have just two wires. When they are connected to a battery the motor will
run as fast as it can, depending on the power supplied and how heavily it is
loaded.
In contrast, a stepping motor has two or more separate coils, and four or more
wires. Each coil causes the motor to turn slightly, usually a few degrees. By
sequentially energizing the coils, the motor can be made to rotate a specific
amount at an accurately controlled speed. Stepping motors give us the ability to
precisely control the rotational position and speed of the motor shaft.
The Experimenter is designed to directly drive up to four DC motors or two
stepping motors at the same time, with supply voltages from 4.5 to 36 volts and
maximum currents of 1 amp across each coil. With some additions the Experimenter can drive more motors and higher currents.
Driving DC Motors
The Experimenter is designed to drive DC motors in an H-bridge configuration. Figure 6-1 shows an H-bridge, in its conceptual form, driving a DC
motor. Of course, the Experimenter uses transistors in the driver chips, U8 and
U9, instead of switches. In this configuration, not only can the power to the motor
be switched on and off, but the polarity of the power can be selected too. This
lets you control the direction of the motor. The direction parameter in the
H-command selects which way the power is routed through the motor.
The H-command also lets you control the speed of DC motors. The speed
parameter does this by varying the duty-cycle of the drivers. The drivers may be
enabled and disabled by a pulse width modulator (PWM). When a driver is
- 43 -
Chapter 6: DC and Stepping Motors
enabled, it provides full power to the motor. When disabled, it provides none.
By rapidly switching the drivers on and off, the power level can be adjusted to
intermediate values. This is less precise than controlling the speed on a stepping
motor, which is done with crystal-clock precision. But it does give you some
measure of control, which is adequate in many applications.
It may prove necessary to adjust the frequency of the PWM to avoid
resonances with the motor’s rotation. The frequency of the PWM is set using the
E-command. The optimum frequency value for a specific motor in a particular
application is best determined by experiment. Low frequencies often cause the
motor to operate in a jerky manner. High frequencies may be limited by the
inductance of the motor.
Because of their internal mechanical brushes, DC motors produce a
tremendous amount of electrical noise. It helps to bypass the high-frequency
energy through nonpolar capacitors installed across the motor’s power leads. Try
a nonpolar electrolytic capacitor (≥100 µF) in parallel with a disk capacitor
(≥0.1 µF).
+
+
A
C
+
B
DC
Motor
–
D
Figure 6-1: The H-Bridge Circuit
The H-bridge circuit runs the DC motor forward (by closing switches A and D)
or reverse (by closing switches B and C). The driver chips (U8 and U9) use this
configuration, except that transistors are used in place of switches. Since the
motor may be connected in either polarity by this circuit, it is called “bipolar.”
On a bipolar device, both sides of the device are switched by drivers, like the
motor in this figure. On a unipolar device, one lead is connected to a supply,
while the other lead is switched. Some stepping motors require bipolar drivers,
others are designed to accept a unipolar supply.
- 44 -
Chapter 6: DC and Stepping Motors
Separate +SUPPLY and GROUND connections are provided for each
driver chip. Be sure to connect these to an adequate power source. The voltage
drops across the high-side and low-side drivers are approximately 1.2 volts at 1
amp (2.4 volts in a bipolar configuration). You may need to provide a little more
supply voltage to get full speed operation out of your DC motor.
Figure 6-2 shows the connections for driving two DC motors. Note how the
capacitors are installed across the motor and the battery connections to the
driver. The Experimenter can directly drive DC motors with supply voltages
from 4.5 to 36 volts and currents up to 1 amp.
When a DC motor is under a heavy load, its current draw increases. The
current peaks when the motor is stalled. Exceeding the driver’s maximum
current rating, even briefly, will destroy the driver. So, if you are driving a motor
that may be subject to stalling and is operating near the current rating, you may
wish to use the driver circuit given in Figure 6-8
6-8. You will only need half of the
circuit, as it is shown driving the two coils of a bipolar stepping motor, and there
is only one set of coil connections to a DC motor. This circuit will safely drive
several amps, with brief loads of up to five amps. It is discussed more fully in
the section Driving Higher Current Motors.
GND
0
+
Driver A
100 µF
0.1 µF
1
–
+
2
100 µF
3
DC
Motor
0.1 µF
+
DC
Motor
–
+A
Figure 6-2: Directly Driving Two DC Motors
This shows the power supply and motor connections required to drive two DC
motors. The Experimenter can directly drive motors with supply voltages from
4.5 to 36 volts and coil currents up to 1 amp. You must not exceed the voltage
or current ratings, as the driver chip would be very quickly destroyed.
- 45 -
Chapter 6: DC and Stepping Motors
Stepping Motor Coil Configurations
Stepping motors differ in physical size from a fraction of an ounce to many
pounds. They are constructed in various ways, and have a wide range of voltage
and current ratings. A single step for some types will be less than a degree, for
others fifteen degrees or more. Electronic surplus stores often have a variety of
stepping motors available. Usually motors will be labelled with the number of
steps per revolution, although this may instead be expressed as the number of
degrees per step. Motors are also labelled with a coil voltage and current rating,
although some list voltage and coil resistance. The Experimenter can drive most
common stepping motors, either directly or with additional buffering for highcurrent motors.
Figure 6-3
There are four common coil configurations for stepping motors (Figure
6-3).
You may find stepping motors with two coils, three coils, two coils with center
taps, or four separate coils. If you get a stepping motor without a data sheet, you
will need to use an ohm meter and a little experimentation to determine the coil
configuration. Once you know the coil configuration you can connect the motor
to the Experimenter’s drivers. The numbers in Figure 6-3 correspond to
DRIVER-A outputs. You can also connect the motor to DRIVER-B in the same
order. For unipolar stepping motors, the wires labelled Supply must be connected to the power supply. Since the driver outputs default to high when the
Experimenter is powered-on, the Supply wires should be connected to the
positive side of the motor supply. Power should not be applied to the motor when
the Experimenter is off, so it is convenient to use SWP (SWitched Power).
You use the H-command to control stepping motors. You must tell the
Experimenter the coil configuration of the stepping motor so that it can provide
the proper sequencing of outputs. Table 5-2 gives the drive types available for
various coil configurations and supply connections.
Most stepping motors can be successfully driven with several different drive
types. For example, a two-coil bipolar stepping motor can be driven with types
8, 9, 10, or 11. The difference between types 8 and 9 for a bipolar motor is the
direction that the motor will turn. The same is true of types 10 and 11. Types 8
and 9 run the motor in full-step mode. Types 10 and 11 double the resolution of
the stepping motor by running in half-step mode.
A two- or four-coil unipolar stepping motor with its common leads
connected to the + supply can be driven with types 7, 9, or 11. Type 7 (one-phase
drive) minimizes power consumption since only one coil is active at any time,
though this reduces torque. Type 9 (two-phase drive) runs two coils simultaneously, providing somewhat more torque but doubling power consumption.
Type 11 (half-step drive) alternates between driving two coils and one coil,
doubling the resolution.
- 46 -
Chapter 6: DC and Stepping Motors
0
0
1
1
2
2
3
Supply
2-Coil Bipolar
3-Coil Unipolar
0
0
Supply
Supply
Supply
1
1
2
2
Supply
Supply
Supply
3
3
2-Coil Unipolar
4-Coil Unipolar
Figure 6-3: Common Stepping Motor Coil Configurations
Unlike ordinary DC motors which use internal brushes to switch current
between coils, stepping motors bring out wires from each coil to be switched
electronically. There are many ways of configuring coils in stepping motors.
This figure shows the common ones. Using an ohm-meter you can figure out
which leads connect to which coils, and learn the coil configuration for any
motor you may find. The Experimenter can drive all common types of motors.
- 47 -
Chapter 6: DC and Stepping Motors
A Typical Stepping Motor
Figure 6-4
The MOT-S2002 (Figure
6-4) is a high quality, ball bearing stepping motor.
It features a full-step of 1.8° (200 steps per revolution), and can be half-stepped
by the Experimenter at 0.9° (400 steps per revolution). This motor is rated at a
maximum coil current of 400 mA at 24 volts, making it especially easy for the
Experimenter to run the motor at its maximum power. When lightly loaded the
MOT-S2002 can be driven from a supply voltage as low as 5 volts. Figure 6-5
shows how to connect the motor to the Experimenter.
The motor weighs 12 ounces, with an overall length of about 2.3 inches.
Maximum torque is roughly 40 inch-ounces. When any stepping motor steps
very rapidly, the inductance of the coils restricts the power going to the coils
Figure 6-6
(Figure
6-6). This motor cannot run faster than 2 mS per step.
To drive the MOT-S2002 in full step mode use drive type 8, for half step
mode use drive type 10. For example, the command H 0 1 100 15 8 would
drive a motor connected to DRIVER-A (0), in the forward direction (1), for 100
steps (100), at a rate of 15 milliseconds per step (15), in full step mode (8).
Driver-A
GND
Figure 6-4: A Stepping Motor
The MOT-S2002 stepping motor is well
suited to control by the Experimenter.
Total Drive Current for a 14 Volt Supply
0
White
1
Green
5 to 26 volts
2
Black
3
Red
+
+A
Current, Milliamps
400
300
Figure 6-5: Directly Driving a
Bipolar Stepping Motor
100
This shows the power supply and coil
connections required to drive a bipolar
2
3 4 5
7 10
100
Stopped
20
Step Rate, Milliseconds per Step
stepping motor, our MOT-S2002. The
Figure 6-6: Current vs Step Rate
Experimenter can directly drive
Shorter step times result in less current stepping motors with a supply voltage
through the motor. Motor torque is of 4.5 to 36 VDC and coil currents up to
similarly reduced.
1 amp.
200
- 48 -
Chapter 6: DC and Stepping Motors
Limiting Current with Series Resistors
It is often useful to add resistors in series with the coils in a stepping motor.
You may wish to power a six volt stepping motor from a 12 volt battery, either
for convenience or to improve the high speed torque of the motor (the higher
voltage helps overcome the increasing coil impedance due to its inductance). Or
you may wish to reduce the motor’s current draw to allow the Experimenter to
drive it safely within the 1 amp maximum driver current rating (circuits for
higher current drive are given in the next section).
Some of the motor supply voltage is lost in the drivers, about 1.2 volts. Since
an H-bridge configuration drives both high and low sides of the coils, about 2.4
volts is lost when driving bipolar motors.
Sometimes the motor’s label tells the coil resistance. Sometimes the label
specifies maximum coil voltage and current instead of resistance, so you can
Equation 6-1
calculate the coil resistance from Ohm’s Law (Equation
6-1). Or you can
measure the resistance with an ohmmeter.
Eq. 6-1:
Rcoil = Ecoil-max / Icoil-max
Rcoil
the internal resistance of the coil
Ecoil-max the maximum rated coil voltage
Icoil-max the maximum rated coil current
Now, using another form of Ohm’s law, we can calculate the additional
series resistance required:
Eq. 6-2:
Rseries = (Esupply - Edrop) / Ichosen - Rcoil
Rseries
Esupply
Edrop
Ichosen
Rcoil
the additional resistance required
the power supply to the driver.
the voltage drop across the driver, about 1.2 volts
unipolar, 2.4 volts bipolar.
the new coil drive current.
the internal resistance of the coil.
Now we need to calculate the power that will be dissipated in the resistors:
Eq. 6-3:
Presistor = (Ichosen)2 * Rseries
Presistor is the power dissipated in the resistor.
Ichosen
the new coil drive current.
Rseries
the additional resistance required
Choose the standard resistor closest to the value calculated in Equation 6-2
6-2.
A good rule of thumb is to get resistors rated for twice the power calculated in
Equation 6-3
6-3. Even so, they will get hot! You may also use series or parallel
combinations of resistors to get the desired values. Figure 6-7 shows a unipolar
stepping motor with series resistors directly connected to the Experimenter.
- 49 -
Chapter 6: DC and Stepping Motors
GND
0
Driver A
Rseries
1
Esupply
+
2
Rseries
3
+A
Figure 6-7: Driving a Unipolar Stepping Motor through Series Resistors
This shows how series resistors may be installed to limit coil current when
directly driving a unipolar stepping motor.
Driving Higher Current Motors
Sometimes you need more power than the 1 amp drivers can give. If so, you
can build a high-current driver. With relatively cheap power transistors, you can
greatly boost the power drive capability of the Experimenter. Figure 6-8 shows
a driver capable of several amps connected to a bipolar stepping motor. The
transistors are connected in an emitter-follower configuration. This configuration provides current gain, with the output voltage following the input voltage.
The diodes dissipate the inductive surge produced when a coil is switched off.
Typically power transistors have current gains of 20 or better. So by using more
powerful transistors than the TIP41 and TIP42 (and bigger diodes), you could
drive motors rated up to 20 amps. Calculate the series resistor as shown in the
previous section, but allow for 3 volts of drop across the power transistors
(Edrop = 3).
When driving large currents, lots of power gets dissipated as heat in the
transistors. It is essential that adequate (big) heatsinks be provided for them. If
the transistors get too hot, they will fail. A little heatsink grease between the
transistor and heatsink improves the heat conduction out of the transistor,
helping to keep the semiconductor junctions a little cooler. And for really big
loads, a fan greatly increases the efficiency of a heatsink.
The tab on the TIP41 and TIP42 transistors is connected to the collector. The
collector on the TIP41 is connected to the positive supply. The collector on the
- 50 -
Chapter 6: DC and Stepping Motors
Emitter
Collector
Base
TIP41
TIP42
pinout
+ Supply
to DRIVER +
TIP41
1N4001
1N4001
TIP41
with Heatsink
with Heatsink
Rseries
Motor
Coil
0
1
TIP42
with Heatsink
1N4001
1N4001
TIP42
with Heatsink
TIP41
1N4001
1N4001
TIP41
with Heatsink
with Heatsink
Rseries
Fast
Blow
Motor
Coil
3
2
Esupply +
TIP42
with Heatsink
1N4001
1N4001
TIP42
with Heatsink
Ground
to DRIVER GND
Figure 6-8: A High-Current Bipolar Driver
This simple circuit may be added to the driver outputs on the Experimenter. It
will drive loads of several amps with up to 36 volts on the supply. Each active
transistor dissipates about 1.5 watts in heat for each amp of current drawn, so
good heatsinks are required. Add heatsinks to all eight of these transistors.
Warnings: The collector shorts to the tab on these transistors! Do not let the
heatsinks on the NPN transistors touch those on the PNP transistors or there
will be a short circuit from the supply to ground. Also, be sure to send the
+Supply and Ground to the driver on the Experimenter as shown.
- 51 -
Chapter 6: DC and Stepping Motors
Emitter
Collector
Base
TIP42
pinout
+ Supply
to DRIVER +
RBase
RBase
1N4001
0
1
1N4001
TIP42
TIP42
with Heatsink
with Heatsink
1N4001
1N4001
RSeries
TIP42
TIP42
with Heatsink
with Heatsink
1N4001
2
3
1N4001
RBase
RBase
Fast
Blow
1N4001
1N4001
RSeries
+
Esupply
Ground
to DRIVER GND
Figure 6-9: A High-Current Inverting Unipolar Driver
This circuit differs from the bipolar driver of Figure 6-8 in that the transistors
are driven to saturation. This results in a lower voltage drop across the
transistors than in the emitter-follower configuration. You will need to calculate
values for the base resistors on each transistor. A base current of about 5% of
the collector current is a good starting point.
Good heatsinks are required on all four of these transistors. Since the collectors
on these transistors short to their mounting tabs, use separate heat sinks for each
transistor.
You must also connect the positive supply and ground to the inputs on the driver
IC. Do not apply power to this circuit without providing power to the Experimenter.
- 52 -
Chapter 6: DC and Stepping Motors
TIP42 is connected to the negative supply. You may use individual heatsinks on
each transistor. Or you may use the same heatsink for the four TIP41 transistors
and another heatsink for the four TIP42 transistors. But do not use the same
heatsink for all eight transistors as this would short the positive supply to the
negative supply.
Unipolar motors do not require quite as complex a driver as bipolar motors.
Figure 6-9 shows a high-current inverting unipolar driver. In this circuit, the
transistors are driven to saturation. This results in lower voltage drop and lower
power loss. Since this is an inverting driver, you should choose a configuration
type for a +supply common unipolar motor, even though the common lead is
connected to ground (see Table 5-2
5-2).
You must calculate values for the base and series resistors. Choose base
resistors that will limit the base current to about 10% of the desired collector
current. Be sure to use appropriately power rated resistors and adequate
heatsinks on the transistors. Use separate heatsinks for each transistor.
Applications of Computer Controlled Motors
We have looked at controlling DC motors and stepping motors with the
Experimenter. What can you build with them? Well, many high school and
college students have built robots controlled by the Experimenter. Gear reduction DC motors make good drive motors for wheels, and stepping motors work
well for positioning sensors.
Some of our customers have automated instruments and machinery using
stepping motors, like telescopes and milling machines. Or adjust the position of
a prism in a spectrascope using a gear reduction stepping motor.
Remember that the Experimenter provides measurement capabilities that
can complement motor control. For example, you can use a potentiometer read
by an analog input to provide feedback on the motor position. Or use a magnetic
switch or hall effect sensor sending a signal to a counter/timer input to count shaft
rotations.
- 53 -
7
Using Analog Inputs
Many sensors output analog voltages. With its eight analog voltage measurement inputs, the Experimenter provides an easy way to interface these
sensors to your computer. This chapter will give you some hints on using these
inputs.
Scaling and Filtering
The two basic operations we must perform on an analog signal are scaling
and filtering. Scaling is adjusting the range of the signal to match the
Experimenter’s input range of 0 to 5.12 volts. Filtering removes noise from the
signal.
Scaling is easily accomplished by using an operational amplifier (opamp)
and resistors to set the gain. The Texas Instruments TLC2274C quad opamp is
Figure 7-1
a very good choice (Figure
7-1). This amplifier has the remarkable property that
its output will swing virtually from one supply rail to the other. By supplying the
amplifier from the 5.12 volt analog supply, the Experimenter’s entire analog
input range can be used. The TLC2274C has very low input bias current of 1 pA
(typical) and low input offset of 300 µA (typical). Its input voltage range is from
-0.3 to 4.2 volts (typical). We use this part in the Observer Meteorological
Station, and it is also available separately from Fascinating Electronics, Inc.
There are many possible opamp circuits. A simple positive gain amplifier
circuit is shown in Figure 7-2
7-2. The circuit gain is given by Equation 7-1
7-1, and
the formula for calculating R2 is given by Equation 7-2
7-2. For example, if you
wanted an amplifier with a gain of 100 and R1 value of 1KΩ, the value needed
for R2 would be 99 KΩ. You may choose the nearest standard value (100 KΩ).
For precision applications, use 1% tolerance resistors.
- 54 -
Chapter 7: Using Analog Inputs
This circuit may be used to scale the output of a temperature sensor or to
amplify the signal from a photodetector (photo diode or transistor). Other opamp
circuits subtract offset voltages from signals or amplify differential signals (for
devices like strain gauges).
Eq. 7-1:
Gain = 1 + R2 / R1
Eq. 7-2:
R2 = R1 * (Gain -1)
The Experimenter’s analog inputs may produce false readings if the voltage
varies at a slew rate of 10 volts/millisecond or greater. This can often be traced
to high frequency electrical noise. Either one or both capacitors, C1 and C2, may
Figure 7-2
be used in the circuit (Figure
7-2) to filter high frequency electrical noise from
the signal. Try values of about 0.1 µF for these capacitors.
Figure 7-1: TLC2274C Quad
Rail-To-Rail Opamp Pinout
The TLC2274C is very useful for
scaling analog signals. It features railto-rail output swing, very low input
current, and low input offset voltage.
Figure 7-2: A Postive Gain Amplifier
By using this simple circuit, you can amplify a signal by even very large gain
factors. R1 and R2 set the gain, C1 and C2 may be used to filter electrical noise.
- 55 -
Chapter 7: Using Analog Inputs
Dual Wiper Potentiometer
In the ANALOG command section (Chapter 4: Command Tutorial), a
potentiometer (pot) was used to create an analog voltage. As the shaft of the pot
rotates, a varying voltage on the wiper may be measured.
As an angle sensor, most pots have two characteristics that limit their
usefulness. They have mechanical stops that limit rotation, usually to about 300
degrees. Pots that do not have mechanical stops are able to rotate freely, but they
have a “dead zone” where the wiper is not touching the voltage divider.
A pot that overcomes both of these problems is available for your experimentation from Fascinating Electronics, Inc. Used primarily in the wind vane
(part of the Observer Meteorological Station), a special pot with two wipers is
available. The wipers are offset 180° from each other, so that one wiper is always
making contact with the voltage divider. A circuit for using the pot is shown
Figure 7-3
(Figure
7-3). The pull-down resistors, R1 and R2, draw the output voltage to
ground when a wiper leaves the voltage divider. C1 and C2 remove any electrical
noise that may be produced as the wipers slide along the voltage divider.
The program (Listing
7-1) converts the Experimenter’s voltage measureListing 7-1
ments into angle values and displays them on the screen. This code must be
Listing 3-2
inserted into the program TEMPLATE.BAS (Listing
3-2) in order to run.
Figure 7-3: Dual Wiper Pot Circuit
The dual wiper pot provides continuous rotation and continuous resolution for
angle measurements. Purchased for the wind direction sensor (part of the
Weather Monitoring Station), the dual wiper pot has many other applications—
robotics, machinery, measurement instruments, and general experimentation.
The resistors pull the wiper voltage to ground when the wiper moves off of the
voltage divider. The capacitors filter electrical noise from the signals.
- 56 -
Chapter 7: Using Analog Inputs
CLS
delta = 700
'delta is the overlap between wipers
DO WHILE UCASE$(INKEY$) <> “Q”
PRINT #1, “A 0”
INPUT #1, w1
'voltage on wiper 1
PRINT #1, “A 1”
INPUT #1, w2
'voltage on wiper 2
LOCATE 1, 1
PRINT USING "#### ####"; w1; w2 'print raw wiper voltages
' Decide if we should update the delta value.
IF w1 > 5120 - 2 * delta AND w1 < 4920 AND w2 < 2 *
delta = (9 * delta + (w2 + 5120 - w1) / 2) / 10
PRINT "w1 > 5120 - 2 * delta AND w1 < 4920 AND w2
ELSEIF w2 > 5120 - 2 * delta AND w2 < 4920 AND w1 <
delta = (9 * delta + (w1 + 5120 - w2) / 2) / 10
PRINT "w2 > 5120 - 2 * delta AND w2 < 4920 AND w1
ELSE
PRINT "No change in delta value.
END IF
delta AND w2 > 200 THEN
< 2 * delta AND w2 > 200"
2 * delta AND w1 > 200 THEN
< 2 * delta AND w1 > 200"
"
' Decide if we have a valid bearing off of one of the wipers.
IF (w1 > delta AND w1 < 5120 - delta) AND (w2 > 5120 - delta OR w2 < delta) THEN
PRINT "w1 yields valid bearing."
bearing = 180 * (w1 - delta) / (5120 - 2 * delta)
ELSEIF (w2 > delta AND w2 < 5120 - delta) AND (w1 > 5120 - delta OR w1 < delta)
THEN
PRINT "w2 yields valid bearing."
bearing = 180 + 180 * (w2 - delta) / (5120 - 2 * delta)
ELSE
PRINT "Do Not Update Bearing. "
END IF
' Print current results for bearing and delta.
PRINT USING “Bearing = ###.# Delta = ####.#”; bearing; delta
LOOP
Listing 7-1: POT-CODE.BAS, Converts Dual Wiper Potentiometer
Voltage Measurements to Angles
This program reads the wiper voltages on a dual wiper pot connected to analog
inputs 0 and 1, and converts the measured voltages to a bearing in degrees. This
Listing 3-2
code must be inserted in TEMPLATE.BAS program (Listing
3-2) in order to run.
The program constantly measures and crosschecks the voltages on the wipers.
If one voltage is midrange, the other should be about 0. As one voltage
approaches an extreme, the other should be near the other extreme. The variable
delta is a measure of the amount of overlap where both wipers are on the resistive
band while they are near the extremes. When both wipers are solidly on the
resistive material the program updates the value of delta
delta, giving a more accurate
reading for your particular potentiometer.
- 57 -
!
Prologue to the Applications
The following chapters show a few examples of projects that have been built
using the Experimenter. Fascinating Electronics Inc. stocks cases and other
accessories, motors, ultrasonic ranging components, temperature, pressure, and
humidity sensors, and many complete kits related to the Experimenter. Some
projects require much larger programs than can be included in this manual, so
sample programs are available on our application disks at very reasonable prices.
With appropriate sensors and motors the Experimenter can link your computer
to the physical world in many ways.
If you have built something with the Experimenter that others may find
interesting or useful, please let us know. We would like to include your
application in our manual or in other publications. If you have developed some
neat software you wouldn’t mind sharing with others, we would like to add it to
the application disks.
We hope the Experimenter will more than live up to your expectations. A
world of new computer applications awaits your creativity. Building devices that
link to the physical world is challenging, fascinating, and educational. Take the
following chapters as a starting point. But remember that applications for the
Experimenter are truly only limited by your imagination.
- 58 -
A
An Ultrasonic RADAR
This is a fun project that puts a live-action RADAR display on the screen
of your computer. We’ve shown this project to a wide range of people—from
kids to seniors, from the computer illiterate to operating system software
consulting engineers. And so far, everyone has been impressed.
The RADAR uses an ultrasonic rangefinder to measure the distance to
surrounding objects. A stepping motor rotates the rangefinder, giving 360°
coverage. Your computer paints a graphic display of the surroundings. VGA and
EGA systems use color for a better-looking display. CGA and Macintosh
systems and are supported too. Figure A-1 shows the RADAR on a VGA display.
The Ultrasonic Rangefinder
We use the same ultrasonic rangefinder that is used on Polaroid cameras.
The rangefinder emits a brief pulse of high frequency sound. Any object hit by
the sound produces an echo. The distance to the object is measured by very
accurately timing from the pulse to the echo.
The Polaroid rangefinder is made up of two parts, a transducer and a driver
Figure A-2
board. The transducer (Figure
A-2) acts as both a speaker and a microphone. It
Figures A-3
emits the sound pulse and listens for the echo. The driver board (Figures
and A-4
A-4) provides the high voltages required to run the transducer, sensitive
amplifiers for echo detection, and control logic.
The Experimenter controls the driver board, measures the time to the echo,
controls the stepping motor that rotates the transducer, and communicates with
your computer. Figure A-5 shows the connections between the transducer,
driver board, and the Experimenter.
- 59 -
Application A: An Ultrasonic RADAR
Figure A-1: The RADAR Display
This is how the radar display looks on a VGA display, minus color enhancements.
The software will also work on EGA and CGA displays, though at lower
resolution. Both the range of the display and the number of points in the scan can
be varied on-the-fly. Available on Application Disk #1.
Figure A-2: The Ultrasonic Transducer
The ultrasonic transducer acts as both a speaker and microphone. The (+)
terminal connects to the E1 output of the driver board, the (–) terminal to E2.
Dimensions are given in inches.
- 60 -
Application A: An Ultrasonic RADAR
Figure A-3: Driver Board Schematic
The driver board provides the high voltages required to run the transducer,
sensitive amplifiers for echo detection, and control logic.
Figure A-4: Driver Board Component Location Diagram
This shows the location of components on the driver board. Dimensions are in
inches.
- 61 -
Application A: An Ultrasonic RADAR
DRIVER BOARD
EXPERIMENTER
1
GROUND
GND
2
GROUND
BLNK
4
DIGITAL I/O A0
INIT
7
T IN 1
ECHO
T IN 0
8
DIGITAL I/O A1
330 µF
+
+5 LOGIC SUPPLY
TRANSDUCER
9
BINH
330 µF
+
+5 LOGIC SUPPLY
+
E1
–
E2
Figure A-5: RADAR Schematic
This shows the connections between the Experimenter, driver board, and
ultrasonic transducter. The Experimenter and driver board link through a
supplied nine pin flex cable.
The driver board interfaces through a nine conductor flex cable. The
connector for this cable can be installed in the X1 connector mounting area on
the Experimenter. The cable has a black stripe on it to indicate pin 1. Do not
substitute for this cable! We have found that crosstalk and voltage drop in
substitute cables is the major cause of these projects not working.
After you wire the connections and install the flex cable, but before applying
power, verify your work with an ohmmeter. Verify that each signal on the
Experimenter shown in Figure A-5 goes to the appropriate pin on U2 in
Figure A-3
A-3.
The driver board’s power requirements are normally under 100 milliamps,
but peak at about 2 amps during the transmit period. To handle this peak demand,
two capacitors of 330 µF or greater must be added: one across the power inputs
on the driver board, and one by the flex cable connector on the Experimenter.
Timing for the rangefinder is shown in Figure A-6
A-6. When the Experimenter
sets INIT high, the driver board sends a burst of sixteen high-voltage drive pulses
- 62 -
Application A: An Ultrasonic RADAR
INIT
XDCR
BINH
ECHO
1 mS
➛
➛
Measured
Time
➛
➛
Figure A-6: Timing Diagram
The Experimenter sets INIT high, causing the driver board to send pulses to the
transducer. The Experimenter waits one millisecond for the pulse transmit and
for the transducer to settle down. The Experimenter sets BINH high to start the
driver listening for an echo. If an echo is heard, the driver board sets ECHO high.
The Experimenter measures the time from BINH going high to ECHO going high.
to the transducer. You may be able to hear this burst as a click. It take about 360
microseconds to transmit the pulses. The Experimenter waits for one millisecond to allow time for pulse transmit and for the transducer to settle down. The
Experimenter then sets BINH high to start the driver listening for an echo. If an
echo is detected the driver board sets ECHO high. The Experimenter measures
the time from BINH going high to ECHO going high. Then the Experimenter
resets INIT and BINH low. If no echo is detected in a reasonable length of time,
the Experimenter terminates the measurement.
The measured time is sent to your computer, which calculates the distance
based on the speed of sound. The speed of sound is approximately 1100 feet per
second, but varies with temperature, humidity, and barometric pressure. You can
calibrate your rangefinder by placing an object a carefully measured distance in
front of the transducer and adjusting the speed of sound parameter in the
software. This is discussed later in the section on software. Since the Experimenter measures time with 10 microsecond resolution, the rangefinder can
measure distance with about 0.07 inches resolution!
- 63 -
Application A: An Ultrasonic RADAR
Stepping Motor
This project uses a stepping motor to rotate the ultrasonic transducer. A slip
ring maintains electrical connection with the transducer. This lets the RADAR
scan in precise increments, with full 360° coverage. You can use a wide variety
of stepping motors. The MOT-S2002 bipolar stepping motor, available from
Fascinating Electronics Inc., works very well. If you provide your own motor be
aware that some of the smallest stepping motors may have trouble reliably
pointing the transducer, due to their limited ability to overcome the inertia of the
rotating mass. But a stepping motor like the MOT-S2002 will have more than
enough torque and can be run at a fraction of its rated power.
The beam from the rangefinder is roughly 10° wide (at its -10 dB points),
so stepping less than about 5° does not necessarily give you much additional
resolution. The software lets you select the number of motor steps between
readings, so you can easily adjust for the optimum resolution. If you use a
different motor, the RADAR program must be told the drive type and the number
of steps per revolution the motor will make with that drive type. This is covered
later, in the RADAR Software section.
Mechanical Assembly
The ultrasonic transducer must be mounted on the stepping motor shaft, and
electrical connections between the transducer and the driver board must be
made. Figure A-7 is a photograph of one way of doing this.
This method requires a brass tube of ¼" inside diameter, a short section of
brass tube that will fit around the first tube with electrical insulation between
them, a plastic cap to surround the transducer, and an alternator brush assembly
to complete the slip ring. You can find these parts at hobby, hardware, and
automotive parts stores. There are many types of alternator brush assemblies
available. Look for one that would be easy to mount on the stepping motor, with
few features that will get in the away.
Drill a hole in the side of a plastic cap and glue the ¼" ID brass tube in it.
The driver board has two wires with clips. Remove these wires from the driver
board and clip them on the transducer. Solder the wire from the negative (-)
terminal of the transducer (see Figure A-2
A-2) to the brass tube. Run the positive
wire from the transducer, through the tube, and out through a hole drilled in the
side of the tube. Mount the transducer in the lid by surrounding it with foam
weather stripping.
Secure a short ring of the slightly larger diameter brass tubing around the
long brass tube, but insulated from it with electrical tape. Solder the positive wire
to this ring. Slip the tube over the motor shaft and secure it with epoxy.
- 64 -
Application A: An Ultrasonic RADAR
Figure A-7: RADAR Mechanical Assembly
A stepping motor rotates the ultrasonic transducer to scan the surroundings for
the RADAR display. Alternater brushes are used for a slip-ring, allowing the
transducer to rotate continuously, but still maintain electrical contact with the
driver board.
- 65 -
Application A: An Ultrasonic RADAR
Mount the alternator brush assembly on the stepping motor so that one brush
contacts the ring, and the other contacts the tube. You may have to add spacers,
and cut, file or sand off features from the brush assembly to get it to fit on the
motor. Then connect terminals E1 and E2 from the driver board to the brushes.
E1 must connect to the ring, E2 to the tube. Verify that there are no opens or
shorts by using an ohmmeter.
RADAR Software
This section includes a short program that measures distances with the
rangefinder. But because the RADAR display program is quite long, it is not
included in this book. You wouldn’t want to type it in anyway! It is on
Application Disk #1, along with the programs in this book. Windows and
Macintosh versions are also available. If you are using a different computer
(Atari, Commodore, Cray, etc.), you will need to translate the program to the
dialect of BASIC used by your machine.
Listing A-1 is a simple distance measurement program. It pulses the
rangefinder several times per second and reports the distance measured with 0.07
inch resolution. You can calibrate the unit to the speed of sound for your local
conditions by placing a flat object, like a book, a carefully measured distance
from the transducer. When you run the program:
If the reported distance is more than the actual distance, decrease the speed
of sound parameter. Pressing the 1 key decreases the parameter 10 feet-persecond (fps), the 2 key decreases 1 fps.
If the reported distance is less than the actual distance, increase the speed
of sound parameter. Pressing the 4 key increases 10 fps, the 3 key increases 1 fps.
You may give the value you determined for the speed of sound to the
RADAR program to make it more accurate. You also need to tell the RADAR
program the drive type for the motor you are using and the number of steps per
revolution it will make at that drive type, which COM port and baud rate to use,
and whether to display in black-and-white or color. All of this information is set
in a file called RADAR.DAT, included on Application Disk #1. You may edit
the file with any text editor, then save it in ASCII format. The RADAR program
will look for this file in the local directory, and set itself up accordingly.
The RADAR display program is easy to run. Pressing the L-key makes the
displayed range longer (up to 35 feet). Pressing the S-key makes the range shorter
(down to 5 feet). Pressing the M-key puts more points in the scan (up to the
resolution of the motor at that drive type). Pressing the F-key puts fewer points
in the scan (down to a minimum of at least 12, depending on motor resolution).
The Windows and Macintosh versions use on-screen buttons for these functions.
- 66 -
Application A: An Ultrasonic RADAR
' This program instructs the Experimenter to initiate an ultrasonic pulse,
' measure the return time, and convert that time nto a distance.
feetPerSec! = 1100
blanking! = .001
'Speed of sound, in ft/sec.
'Blanking time, in seconds.
' Print the header.
CLS
PRINT "Type Q to Quit."
LOCATE 8, 30, 0
PRINT " Ultrasonic Ranging "
LOCATE 9, 30, 0
PRINT "---------------------"
PRINT #1, "D 3 139"
'DIGITAL I/O port A is output.
DO
PRINT #1, "D 0 0 100 1 1 3" 'Wait 100 mS, then make a pulse.
PRINT #1, "C 0 11"
'Measure the echo delay.
INPUT #1, time!
'Measurement units are 10's of uS.
time! = time! / 100000 + blanking!
PRINT #1, "D 0 0"
'Turn off ultrasonic rangefinder.
' Calculate and Print the results.
distance! = time! * feetPerSec! / 2
LOCATE 10, 30, 0
PRINT USING "Time = 0.###### sec"; time!
LOCATE 11, 30, 0
PRINT USING "Distance = ##.## ft"; distance!
LOCATE 12, 30, 0
PRINT USING "Speed =
#,### ft/s"; feetPerSec!
' Check for change of value for speed of sound.
key$ = UCASE$(INKEY$)
SELECT CASE key$
CASE "1"
feetPerSec! = feetPerSec! - 10
CASE "2"
feetPerSec! = feetPerSec! - 1
CASE "3"
feetPerSec! = feetPerSec! + 1
CASE "4"
feetPerSec! = feetPerSec! + 10
CASE "Q"
END
END SELECT
LOOP
Listing A-1: DISTANCE.BAS, Distance Measurement Code
This simple program measures and displays the distance from the ultrasonic
transducer to an object. Minimum distance is about half a foot. Maximum
distance is about 35 feet. Resolution is 0.07 inches. You can use this program to
determine the speed of sound for your current local conditions. In order to run,
this code must be surrounded with the TEMPLATE.BAS program, Listing 3-2.
- 67 -
B
Observer Meteorological Station
The weather affects everyone. But instead of simply being a source of
rained-out picnics, the weather can be a source of endless fascination. Weather
is a constantly changing panoply of winds, heat, pressure, and moisture. This
project is a professional caliber meteorological station that can help you unlock
the secrets of weather. These stations are in use in many countries for such
diverse applications as greenhouse automation, Earth science projects, agricultural surveys, as well as basic meteorological data collection.
Rugged Meteorological Instruments
At Fascinating Electronics Inc., we designed a meteorological station that
is both fun to build and to use. We developed kits for all of the standard
meteorological measurements. They are available separately, or together in a
package we call the Observer.
Figure B-1
Figure B-2
B-2),
The Observer system (Figure
B-1) includes an anemometer (Figure
Figure B-5
Figure B-3
Figure B-4
wind vane (Figure
B-3), rain gauge (Figure
B-4), thermometers (Figure
B-5),
Figure B-6
Figure B-7
B-7). The Experimenter is
hygrometers (Figure
B-6), and a barometer (Figure
housed in a sturdy metal case, along with the barometer and signal conditioning
electronics.
All instrument calibration is performed on your computer. This makes the
instruments much simpler, easier to build, and reduces their cost while providing
great accuracy.
Instruments are rugged, made with heavy gauge PVC, and with extensive
use of stainless steel hardware. The anemometer and wind vane feature shielded
steel ball bearings for measurement sensitivity and durability. The temperature
- 68 -
Application B: Observer Meteorological Station
Figure B-1: The Observer Meteorological Station.
Full-size instruments featuring extensive use of stainless steel hardware and
heavy gauge PVC are tough, made to last. The Experimenter provides the
interface between the instruments and the computer.
sensors use current output (rather than voltage output) integrated circuit sensors,
for accuracy that does not degrade with long cable lengths. The barometer and
humidity sensors also use reliable solid-state sensors.
This is not a disposable weather station! If any instrument should break it
can be repaired. All instruments can be disassembled and any broken components replaced. If you can build it, you can fix it.
This is a project that will give you many years of satisfaction. It will provide
you with a record of exciting storms, details on your own microclimate, and a
deeper understanding of the world around you.
These few pages will give you some idea of the construction and capabilities
of the Observer. Unfortunately, we do not have space to go over the construction
in detail as we did with the Ultrasonic RADAR. If you would like more
information, please take a look at our website where you can find photos and
download assembly instructions.
- 69 -
Application B: Observer Meteorological Station
¼"-20 ACORN NUT
¼" FLAT WASHER
DISK MAGNETS
NYLON SPACER
TWO ¼" FLAT WASHERS
BALL BEARING
¼"-20 BY 1-½" STAINLESS
STEEL BOLT
2" PVC ROTATING CAP
MAGNETIC SWITCH
Tighten Nuts Gently!
1-½" PVC STATIONARY CAP
ALUMINUM WIND CUP (ONE OF 3)
NYLON WASHER (4 PER WIND CUP)
#8-32 BY 4" STAINLESS
1-½" PVC PIPE
#8-32 STAINLESS HEX NUT & NYLON WASHER
#8-32 STAINLESS HEX NUT & LOCKWASHER
Rev. H
© 1996-2000 by Fascinating Electronics Inc.
Figure B-3: Wind Vane.
Even a gentle breeze turns this precise
and sensitive wind vane. With a beautiful
laser-cut gold anodized aluminum tail,
shielded steel ball bearings, stainless
steel hardware and ball bearing, custom
molded
powdercoated
lead
counterweight and rugged schedule 40
PVC body this instrument is built to
withstand the elements. A special dualwiper potentiometer translates the wind
direction into two voltages, with 1°
resolution and no “dead band.”
Figure B-2: Anemometer.
From gentle zephyr to full gale, this
rugged three-cup anemometer
accurately measures wind speed. Tested
in hurricane force winds. Built of robust
precision drilled schedule 40 PVC, three
full-size (3") aluminum wind cups, with
shielded steel ball bearings and
stainless steel hardware. Output is a
magnetic switch closure.
WIND VANE
#8-32 BY 3" STAINLESS
LARGE NYLON SPACER
#8-32 BY 1/2" STAINLESS
WITH NYLON WASHER
HEX NUT AND LOCKWASHER
2" PVC ROTATING CAP
STREAMLINED LEAD
WEIGHT
BALL BEARING
SMALL NYLON SPACER
#8 EXTERNAL TOOTH LOCKWASHER
#8-32 BY 1/4" STAINLESS
WITH NYLON WASHER
1-1/2" PVC CAP
5/32" BY 2" RUBBER TUBE
DUAL WIPER POTENTIOMETER
#8 BY 1/2" STAINLESS SMS
POTENTIOMETER MTG. BRACKET
BLUE
YELLOW
GREEN
RED
ANEMOMETER
1-1/2" BY 5" PVC PIPE
Rev. J
© 1994-2000, Fascinating Electronics Inc.
RAIN GAUGE
SPLASH
SHIELD
ADHESIVE/
SEALANT
FUNNEL
ADHESIVE/
SEALANT
STAINLESS SMS
PIPE
RECTANGLE/
ROUND
ADAPTER
MAGNETIC
SWITCH
MAGNET
STAINLESS
MACHINE SCREWS
WITH HEATSHRINK
COLLECTOR
ALUMINUM
MOUNTING
BRACKET
FOAM TAPE
BRASS PIVOT
PIECE OF
BACKING PAPER
Rev. I
- 70 -
© 1994-2001, Fascinating Electronics Inc., All Rights Reserved Worldwide
Figure B-4: Rain Gauge.
From drought to flood, this selfemptying rain gauge keeps the rainfall
tally. With its large diameter funnel, it
is sensitive to less than 0.01" of rain.
Metal splash shield, mounting brackets
and rain collector for durability. Sturdy,
heavy gauge plastic base and funnel.
Tested to rainfall rates exceeding 4
inches per hour. When a precise amount
of rainwater collects, the collector tips,
triggering a sealed magnetic switch.
The calibration value is entered in
software for best accuracy.
Application B: Observer Meteorological Station
Figure B-5: Temperature Sensors.
A tiny integrated circuit temperature
sensor accurately converts the ambient
temperature into a current. Output is a
current, rather than a voltage, allowing
almost any length of wire to connect the sensor to the Observer meteorological
station. The sensor is sealed in a moisture-tight adhesive lined heat shrink tube
for long life.
Figure B-6: Temperature plus
Humidity Sensors.
This approximately ½" by 2-½" circuit
board supports circuitry for both one
temperature sensor and one humidity
sensor. A capacitive element changes
in value in response to the relative humidity of the air. This capacitance is
translated into a digital frequency by an integrated circuit timer. The timer and
temperature sensor are sealed in hot-melt adhesive and heat shrink.
Figure B-7: Signal Conditioning and Barometer Board.
Filters signals from the weather instruments for measurement by the Experimenter.
This small circuit board mounts on the Experimenter, over the wiring grid. The
wind instruments, rain gauge, and single temperature/humidity sensor connect
through modular jacks. The additional temperature/humidity sensors plug in
through a DB25 connector. A solid-state barometer on the board measures local
air pressure, can be temperature compensated for high precision over wide
temperature changes, and can be adjusted over a very wide elevation range.
- 71 -
Application B: Observer Meteorological Station
Figure B-8: Current Weather Display.
The current weather display shows: (top row, left to right) wind speed moving
graph, five thermometers, daily rainfall, (lower row) two hygrometers, barometric
pressure, and wind direction. Digital values are displayed below each instrument
graphic. Wind chill and dew point are also presented.
Meteorological Station Software
A very easy to use menu driven program runs the Observer. Graphical
Figure B-8
instruments display the current conditions (Figure
B-8). The software automatically stores weather data on your computer’s hard drive. You can graph the
results (Figure B-9
B-9). The past day’s minimum and maximum records are
Figure B-10
displayed with 1 minute resolution (Figure
B-10).
Data is stored each minute for the past 24 hours, giving a detailed recap of
the past day’s weather and providing a basis for estimating weather trends.
Hourly data and daily minimum and maximum records are permanently stored
for historical analysis, and can be graphed or exported to other programs for
further analysis.
The Experimenter’s high current drivers and relay can be used as alarms,
easily configured for a variety of weather conditions.
- 72 -
Application B: Observer Meteorological Station
Figure B-9: Past 24 Hour History.
This is an actual data graph from a recent Pacific storm. Relative humidity (top
line) hovered just below 90% most of the afternoon, except when the sky cleared
between 4 PM and 5 PM, allowing the temperature (third from top) to rise from
43°F to just over 52°F, before falling back to 43°F as the sun set. The barometer
(second from top) fell steadily, warning of an approaching front. The first 5 MPH
wind gusts from the front appeared about 10:15 PM, and grew stronger
throughout the night. Winds peaked at just under 20 MPH at 1 AM and again at
around 7 AM.
Figure B-10:
Daily Minimums &
Maximums Display.
The time and value of the daily
minimum and maximum for
each instrument are displayed
with one minute resolution.
Rainfall month-to-date and
year-to-date are also presented.
- 73 -
C
An Autonomous Robot
This fascinating project was built as a metal shop project by high school
students in Newberg, Oregon. The robot is operated by an internal computer, and
includes a speech synthesizer, keyboard, and video display.
Hardware Features
The robot has two arms which rotate at the shoulder and bend at the elbow.
A simple gripper is mounted on the end of each arm. All three functions
(shoulder, gripper and elbow) are controlled by stepping motors. High current
drivers were built for some of these motors.
In order to control six stepping motors from one Experimenter the students
built a latching driver circuit. The circuit takes the T-OUT signals in two groups
(0:3, 4:7), and either latches or passes the signals to driver ICs. In this way both
arms can make the same motion simultaneously, or may move independently
one at a time.
The waist rotates, driven by a small DC motor. DC motors were also used
to drive the main wheels, which were originally built for a child’s electric car.
The robot’s “brain” is a PC motherboard. A text-to-speech synthesizer is
driven through a printer port. A small monochrome monitor and 3.5" floppy
drive mount in the robot’s head. Speakers for the speech synthesizer mount on
the robot’s shoulders.
A 12 volt automobile battery provides power the motors and electronics. A
switching supply generates 5 volt power for the computer. +12 volts required
by the monitor is supplied through a 1 amp low dropout voltage regulator.
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Application C: An Autonomous Robot
Possible enhancements include adding microswitches to detect collisions
with objects by the body or the arms, and adding an ultrasonic RADAR for
obstacle avoidance. The software can be endlessly enhanced, adding new and
interesting behaviors.
Mechanical Hints
The Newberg High School students work with very good shop equipment.
Few of us are so fortunate. If you want to build a robot but lack metal working
machinery, why not try working out a deal with your local high school or
community college industrial arts teacher? He may be receptive to doing a
project like this.
Based on the student’s experience, it is difficult to build to tolerances
adequate for gear drive. The students had much more success with belt drive.
Where subject to great tension, such as at the shoulder joint, a belt with large
teeth is needed to prevent slippage. A modest reduction ratio can provide a great
deal of torque from even small stepping motors. Aluminum is much lighter than
steel. Even so, it is amazing how much a five foot tall robot can weigh.
Almost all of the mechanical parts were acquired surplus. Some were
scavenged from copy machines. The robot was basically built from scrap that
had been donated to the high school. Despite its humble origins, the robot was
a great success. The students learned not only machining, but also electronic
wiring and BASIC programming.
Figure C-1: The Newberg High School Robotics Team.
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Experimenter Specifications
11/02/2001
Serial Interface
Standard RS-232C, DB-25 female connector.
Supports baud rates from 300 baud to 38.4 Kbaud
with hardware and Xon/Xoff handshake.
Drivers
Eight drivers, source and sink up to a maximum of
1 amp each. Uses an external power source of
+4.5 to +36 volts DC. Thermal overload and output
clamp diode protected. Not short circuit protected.
Relay
One SPDT relay with LED status indicator, for
loads up to 10 amps.
Analog Inputs
Eight analog channels with 5 millivolt resolution
from 0 to 5.115 volts.
Counter/Timers
Four counter/timers. Resolution is 10 µS, durations
from 250 to 655,350 µS. Measures period, pulse
width, channel-to-channel delay. Counts to 65,535
from DC to >1 kilohertz.
Digital I/O
Twenty-four digital input/output lines with CMOS
voltage and drive levels.
Logic Supply
A low dropout voltage regulator provides +5 volts
for Experimenter logic circuitry from an external
supply of +5.5 to +15 volts. Has LED power
indicator and convenient power switch.
Analog Supply
An adjustable low dropout voltage regulator
provides a quiet, precise, 5.120 volt reference and
power supply for analog measurements and
circuits.
Circuit Board
Durable epoxy-glass, double-sided with plated
holes. Circuit numbers, graphics and solder mask
on both sides. Measures approximately 5.25 by 6.2
inches. Rests on six rubber feet or may be installed in an optional metal case.
Wiring Grid
Large wiring grid (360 pads) with prewired +5 and
GND pads for adding your own circuits. Also has
mounting pads for adding one DB-25, two DB-9,
one high density and one 5 mm pitch connectors.
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