alarm systems

alarm systems
CHIP FACTORY ALARM PROJECT
1
ALARM SYSTEMS
What is a microcontroller?
A microcontroller is often described as
a 'computer-on-a-chip'. It can be used
as an ‘electronic brain’ to control a
product, toy or machine.
The microcontroller is an integrated circuit
("chip") that contains memory (to store the program), a
processor (to process and carry out the program) and input/
output pins (to connect switches, sensors and output devices like motors).
Microcontrollers are purchased 'blank' and then programmed with a specific control
program. This program is written on a computer and then 'downloaded' into the
microcontroller chip. Once programmed the microcontroller is built into a product to
make the product more intelligent and easier to use.
Example use of a microcontroller.
Almost all modern buildings are fitted with some type of alarm. For
instance a fire detection system may have a number of smoke sensors
to detect the smoke from a fire.
However many alarm systems are also safety systems - for instance an
alarm system on an oil rig may monitor the temperature and pressure
of the crude oil as it is being extracted and automatically shut
the system down if a fault is detected. This ensures the safety of
both the workers and the environment around the oil rig.
All systems are made up of input and output devices. Often
these devices are connected to a microcontroller that interprets
the information from the sensors and switches the outputs on
and off at the correct time.
1
4
7
*
In the case of a fire alarm system the inputs may be smoke
sensors and the keypad on the front of the control panel. The
output devices are the display on the control panel as well as
the external siren and strobe light. The microcontroller is the
'brain' of the system.
2
5
8
0
3
6
9
#
A
B
PI
C
AL AX
AR E
M
C
D
Microcontrollers are powerful electronic components that have a
memory and can be programmed to switch things on and off in a
special sequence. The microcontroller in the fire alarm, for
instance, has been programmed to switcyh the siren on and off
when the smoke sensor has detected fire.
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2
BLOCK DIAGRAMS
The electronic system that makes up the alarm system be drawn as a ‘block diagram’.
INPUT
PROCESS
OUTPUT
3
smoke
microcontroller
siren
0
8
#
9
6
2
5
7
4
1
keypad
strobe
LCD
The smoke sensor and keypad provide information to the microcontroller, and so these
are known as ‘inputs’. The microcontroller then ‘decides’ how to behave and may then
operate the outputs e.g. make the siren and strobe switch on or display a message on the
Liquid Crystal Display (LCD).
WHAT IS THE CHIP FACTORY SYSTEM?
The microcontrollers used in devices such as the alarm can be difficult to program, as
they generally use a complicated programming language called ‘assembler code’, which
can be quite difficult to learn.
The Chip Factory system makes the microcontrollers much easier to program. The
control sequence can be written in a simpler programming language called BASIC. This
makes it much easier to use the microcontroller as the complicated ‘assembler code’ does
not need to be learnt.
A sample BASIC program and flowchart are shown here. In this case both programs do
the same thing - flash a light (connected to output 0) on and off every second.
00
01
02
03
04
high
0
wait 010
low
0
wait 010
goto 00
start
high 0
wait 1
low 0
wait 1
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CHIP FACTORY ALARM PROJECT
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BUILDING YOUR OWN ALARM
Design Brief
Design and make an alarm system. The alarm must be programmed to react to inputs
and sensors.
Design Specification Points
1) The design will use a PIC12F629 microcontroller as it’s brain.
2) The design will include an LED indicator, a piezo sounder to generate noises and an
alarm output that could be a siren or motor..
3) The design will be also be able to react to analogue sensors such as light sensors.
.
Block Diagram
The block diagram for your alarm may look like this:
INPUT
PROCESS
digital
OUTPUT
output
microcontroller
analogue
LED
piezo
Designing Your Alarm
Your alarm may be for any purpose you choose. Some examples are given below.
1) A fire alarm. A light sensor is used to detect smoke. When smoke is detected a siren
sounds.
2) A burglar alarm. When a tripwire is activated a flashing stobe light is activated.
However the alarm is disabled during daylight by a light sensor.
3) A bank safety lock. When a ‘panic’ alarm switch is pushed an electronic solenoid
bolt locks a bank safe door.
4) A baby monitor for a bedroom. When movement or sounds are NOT detected, a
warning buzzer is activated.
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ELECTRONIC COMPONENTS
The main electronic components you may need for your alarm are shown here. The next
few pages describe each of these components in more detail, and also provide some
programming ideas that may be useful when you are later programming your alarm.
PIC12F629 microcontroller
light emitting diode (LED)
piezo sounder
light dependent resistor (LDR)
transistor
and diode
batteries
and you will also need
resistors
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CHIP FACTORY ALARM PROJECT
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SECTION 2 - ELECTRONIC COMPONENTS
MICROCONTROLLERS
What is a microcontroller?
A microcontroller is often described as a ‘computer-on-a-chip’. It is an
integrated circuit that contains memory, processing units, and input/
output circuitry in a single unit.
Microcontrollers are purchased ‘blank’ and then programmed with a specific
control program. Once programmed the microcontroller is built into a
product to make the product more intelligent and easier to use.
Where are microcontrollers used?
MIC
RO
WA
VE
MW
-1
Applications that use microcontrollers include household
appliances, alarm systems, medical equipment, vehicle
subsystems, and electronic instrumentation. Some modern cars
contain over thirty microcontrollers - used in a range of
subsystems from engine management to remote locking!
TIM
E
SE
1
2
3
4
5
FU
LL
ME
D
CLE
T
6
7
8
9
10
HIG
DE
AR
CO
H
F
OK
As an example, a microwave oven may use a single microcontroller to process
information from the keypad, display user information on the seven segment
display, and control the output devices (turntable motor, light, bell and magnetron).
How are microcontrollers used?
Microcontrollers are used as the ‘brain’ in electronic circuits. These electronic circuits are
often drawn visually as a ‘block diagram’. For instance a simplified block diagram for the
microwave above could be drawn like this:
INPUT
PROCESS
door
switch
keypad
switch
pushes
OUTPUT
motor
microcontroller
magnetron
light
bell
The program for the microcontroller is developed (and tested) on the computer and then
downloaded into the microcontroller. Once the program is in the microcontroller it
starts to ‘run’ and carries out the instructions.
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BATTERIES
What is a battery?
A battery is a self-contained source of electronic
energy. It is a portable power supply.
Batteries contain chemicals that store energy.
When connected into a circuit this chemical
energy is converted to electrical energy that can
then power the circuit.
3V
Which battery size should I use?
Batteries come in all sorts of types and sizes. Most
battery packs are made up of a number of 'cells',
and each cell provides about 1.5V. Therefore 4 cells
will generate a 6V battery and 3 cells a 4.5V battery.
As a general rule, the larger the battery the longer it
will last (as it contains more chemicals and so will
be able to convert more energy). A higher voltage
battery does not last longer than a lower voltage
battery. Therefore a 6V battery pack made up of 4
AA cells will last much longer than a 9V PP3 battery, as it contains a larger total amount
of chemical energy as it is physically larger. Therefore items that require more power to
work (e.g. a CD walkman which contains a motor and laser to read the CD's) will always
use AA cells rather than PP3 batteries.
Microcontrollers generally require 3 to 6V to work, and so it is better to use a battery
pack made up of three or four AA size cells. Never use a 9V PP3 battery as the 9V supply
will damage the microcontroller.
Which battery type should I use?
Different batteries are made of different chemicals. Zinc-carbon batteries are the
cheapest, and are quite suitable for many microcontroller circuits. Alkaline batteries are
more expensive, but will last much longer when driving devices like motors that require
larger currents. Lithium batteries are much more expensive but have a long life, and so
are commonly used in computer circuits to provide a clock backup.
Rechargeable batteries can be recharged when they 'run-down'. They are generally made
up of nickel and cadmium (Ni-cad) or nickel metal hydroxide (NiMH) chemicals.
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Safety!
Never 'short circuit' any battery. Alkaline and rechargeable batteries can provide a very
large current, and can get so hot that they will actually melt the battery box if you short
circuit them! Always make sure you connect the battery around the correct way (red
positive (V+) and black negative (0V or ground)). The microcontroller chip will get hot
and be damaged if the battery is connected the wrong way around.
Using battery snaps.
Battery packs are often connected to electronic printed circuit boards by
battery snaps. Always ensure you get the red and black wires the correct
way around. It is also useful to thread the battery snap through holes on
the board before soldering it in place - this provides a much stronger
joint that is less likely to snap off.
Never accidentally connect a 9V PP3 battery to the battery snap - this will
damage the microcontroller, which only works between 3 and 6V.
Soldering to battery boxes.
Some small battery boxes require wires to be soldered to metal contacts on the battery
box. In this case you must be very careful not to overheat the metal contact. If the
contacts gets very hot they will melt the plastic and fall off. A good way of stopping this
happening is to ask a friend to hold the metal contact with a pair of small pliers. The
pliers will act as a ‘heat-sink’ and help stop the plastic melting.
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LIGHT EMITTING DIODE (LED)
What is an LED?
A Light Emitting Diode (LED) is an electronic component
that gives out light when current passes through it. An
LED is a special type of diode. A diode is a component
that only allows current to flow in one direction. Therefore when
using a diode, it must always be connected the correct way around.
The positive (anode) leg of an LED is longer than the negative
(cathode) leg (shown by the bar on the symbol). The negative leg
also has a flat edge on the plastic casing of the LED.
What are LEDs used for?
LEDs are mainly used as indicator lights. Red and green LEDs are commonly used on
electronic appliances like televisions to show if they are switched on or in 'standby'
mode. LEDs are available in many different colours, including red, yellow, green and
blue. Special 'ultrabright' LEDs are used in safety warning devices such as the 'flashing
lights' used on bicycles. Infra-red LEDs produce infra-red light that cannot be seen by the
human eye but can be used in devices such as video remote-controls.
Using LEDs.
LEDs only require a small amount of current to work,
which makes them much more efficient than bulbs (this
means, for instance, that if powered by batteries the LEDs
will light for a much longer time than a bulb would). If
too much current is passed through an LED it will be
damaged, and so LEDs are normally used together with a
'series' resistor that protects the LED from too much
current.
The value of the resistor required depends on the battery
voltage used. For a 4.5V battery pack a 330R resistor can
be used, and for a 3V battery pack a 120R resistor is
appropriate.
pin
330R
0V
Connecting the LED to a microcontroller.
Because the LED only requires a small amount of current to operate, it can be directly
connected between the microcontroller output pin and 0V (with the series protection
resistor).
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Testing the LED connection.
After connecting the LED it can be tested by a simple program like this:
00
01
02
03
04
high
0
wait 010
low
0
wait 010
goto 00
start
high 0
This program would switch the LED (connected to
output pin 0) on and off every second. If the LED does
not work check:
wait 1
low 0
1) the LED is connected the correct way around
2) the correct resistor is used
3) the correct output pin number is being used in the
program
4) all the solder joints are good
wait 1
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BUZZERS AND PIEZO-TRANSDUCERS
What is a piezo transducer?
A piezo transducer is a low-cost 'mini-speaker' that can used to
make sounds. The sound that the piezo makes can be changed
by altering the electronic signals provided by the
microcontroller.
Where are piezos used for?
Piezos are used in many different consumer goods to provide 'feedback' to the user. A
good example is a vending machine which will 'beep' whenever a keypad switch is
pressed to select a drink or snack. The 'beep' provides the user with feedback to tell them
their switch push has been successful. Uncased piezos are also often used in musical
birthday cards to play a tune when the card is opened.
What is the difference between a piezo and a buzzer?
A buzzer contains a small electronic circuit that generates the electronic signal needed to
make a noise. Therefore when a buzzer is connected to a battery it will
always make the same sound. A piezo does not contain this circuit, and so
therefore needs an external signal. This signal can be supplied by the
output pin of a microcontroller. A piezo also requires less current to
operate and so will last longer in battery powered circuits.
Using piezos.
A piezo is very simple to connect. Simply
connect the red wire to the microcontroller
output pin and the black wire to 0V
(ground).
Note that the cheapest piezos do not have a
plastic casing to them. In this case it is
necessary to mount the piezo on a piece of
board (with a sticky pad) to create a noise
that can be heard. The board acts as a
'sound-box' to amplify the sound made by
the piezo. Make sure the sticky pad is stuck
on the correct side of the piezo (the brass side
without the wires!).
pin
pin
+
40R
0V
0V
Making More Noise.
Some times you might want to make a louder noise. In this case it is
possible to use a speaker instead of the piezo. When using a speaker
it is also necessary to use a capacitor (e.g. 10uF electrolytic capacitor)
to prevent damage to the microcontroller.
Remember that, like the piezo, a speaker only works correctly when
mounted in a 'sound-box'.
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Testing the piezo connection.
After connecting the piezo it can be tested by a simple program like this:
00
01
02
03
04
beep
beep
beep
beep
goto
065
078
088
119
00
This program would make the piezo (connected to output 2) make 4 different sounds
(value 65, 78, 88 and 119). If the piezo does not work check:
1) the sound value is between 0 and 255
2) the correct output pin number is being used in the program
3) all the solder joints are good
With the beep command, the number denotes the tone. The higher the tone, the higher
the pitch of the sound (note that some sounders cannot produce very high tones and so
number greater than 200 may not be heard).
The following BASIC program use a loop to produce all the possible sounds, using
variable x to store the sound value.
00
01
02
letx=
x plus 001
out
x
goto 000
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TRANSISTOR
What is a transistor?
C
B
A transistor is a component that controls current flow in a circuit.
A transistor acts as an ‘electronic switch’ so that a small current
can control a large current. This allows low-current devices, like a
microcontroller, to control large current devices (like motors).
emitter (E)
base (B)
collector (C)
E
Where are transistors used?
Transistors are used in radios and electronic toys and many
other devices such as this electronic stapler.
Using transistors.
A transistor has three legs. These are labelled base,
collector and emitter. The base connection is the leg
that is used to activate the ‘electronic switch’. When a
small current is passed through the base connection, it
allows a much larger current to flow down between the
collector and emitter. This larger current can be used to
switch on devices such as motors, lamps and buzzers.
+V
+V
m
small
current
into base
0V
m
0V
A common transistor is the BC548B type. This has a
plastic can with a flat edge. The flat edge enables the base,
collector and emitter legs to be correctly identified.
Using motors.
V+
Motors can generate ‘electrical noise’ as they turn.
This is because the magnets and electric coils inside
the motor generate electrical signals as the motor
rotates. These signals (the electronic noise) can
disrupt the operation of the microcontroller. Some
motors, like solar motors, produce very little noise
whilst others can create a lot of noise.
1N4001
Pin
1k
Output
device
BC548B
0V
To prevent electrical noise affecting the microcontroller circuit a 220nF capacitor should always
be soldered across the motor terminals before it is used.
In addition, a diode (e.g. 1N4001 diode) should be connected
alongside the motor. This prevents damage to the transistor as
the motor slows down after the transistor switches off (for a
short period of time (as it slows down and stops) the motor is
acting as a ‘dynamo’ and generating electric current!). When
connecting a diode make sure the ‘band’ is connected the
correct way around. It is also a good idea to connect a 100uF
electrolytic capacitor across the battery supply to help
‘suppress’ the the electrical noise.
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large
current
across
collector/
emitter
CHIP FACTORY ALARM PROJECT
13
Testing the transistor using a buzzer
A buzzer could be connected as an output device as in this cicruit.
V+
1N4001
pin
1k
(red)
Buzzer
BC548B
0V
After connecting the buzzer it can be tested by a simple program like this:
00
01
02
03
04
low
3
wait 010
high
3
wait 010
goto 00
This program would switch the buzzer (connected to output 3) on and off every second.
If the buzzer does not sound check that:
1)
2)
3)
4)
5)
6)
the diode is connected the correct way around
the correct resistors are used
the transistor is connected the correct way around
the buzzer red wire is connected the correct way around
the correct output pin number is being used in the program
all the solder joints are good
Output Devices
Output devices that can be connected via a transistor include buzzers, motors, solenoids,
sirens and flashing strobe lights. However some devices may need a higher power
transistor - in this case the Darlington transistor BCX38B can be used instead of the
standard BC548B transistor.
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DIGITAL SENSORS (SWITCHES)
What are switches?
A digital sensor is a simple ‘switch’ type sensor that can only be ‘on’ or ‘off’. If a graph is
drawn of the on-off signals as the switch is pushed it will look like this:
Voltage
5V
0V
Time
Switches are electronic components that detect movement. There are a large number of
different types of switches e.g:
push switches that detect a momentary 'push'
micro-switches with long levers that detect small movements
tilt-switches that detect jolting
reed-switches that detect a magnet being moved
What are switches used for?
Push switches are commonly used on device like keypads. Micro-switches are used in
burglar alarms to detect if the cover is removed from the alarm box. Reed switches are
used to detect doors and windows being opened and tilt switches are often used to detect
movement in devices such as toys, hair-dryers and tool-box alarms.
Switch Symbols.
The symbols for a slide switch
and a push switch are shown here.
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Using switches
A switch is used with a resistor as shown in the diagram. The
value of the resistor is not that important, but a 10k resistor
is often used. When the switch is 'open' the 10k resistor
connects the microcontroller input pin down to 0V, which
gives an off (logic level 0) 0V signal to the microcontroller
input pin.
When the switch is activated, the input pin is connected to
the positive battery supply (V+). This provides an on (logic
level 1) signal to the microcontroller.
V+
Pin
10k
0V
Testing the switch
After connecting the switch it can be tested by a simple program like this. This program
will switch an output on and off according to if the switch is pushed or not.
00
01
02
03
04
05
06
if
0 on goto 03
goto 00
high
0
wait 020
low
0
goto
00
‘ jump if the input is on
‘ else loop back around
‘
‘
‘
‘
switch output 0 on
wait 2 seconds
switch output 0 off
jump back to start
In this program the first two lines make up a continuous loop. If the input is off the
program just loops around time and time again.
If the switch is then pushed the program jumps to the line 03. The program then flashes
output 0 on for two seconds before returning to the main loop.
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LIGHT DEPENDENT RESISTOR (LDR)
What is an LDR?
A Light Dependent Resistor (LDR) is special type of resistor that reacts to changes in light
level. The resistance of the LDR changes as different amounts of light fall on the top
'window' of the device. This allows electronic circuits to measure changes in light level.
R(W)
LDR
Light intensity
(Lux)
dark
light
What are LDRs used for?
LDRs are used in automatic street lamps to switch them on at night and off during the
day. They are also used within many alarm and toys to measure light levels.
The LDR is a type of analogue sensor. An analogue sensor measures a continuous signal
such as light, temperature or position (rather than a digital on-off signal like a switch).
The analogue sensor provides a varying voltage signal. This voltage signal can be
represented by a number in the range 0 and 255 (e.g. very dark = 0, bright light = 255).
light
Voltage
5V
dark
0V
Time
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Using LDRs.
A LDR can be used in two ways. The simplest way to use an LDR is
as a simple on-off ("digital") switch - when the light level is above
a certain value (called the 'threshold value') the LDR will provide
an on signal, when the light level is below a certain value the LDR
will provide an off signal.
In this case the LDR is used in a potential divider with a standard
resistor. The value of the standard resistor sets the 'threshold value'.
For miniature LDRs a suitable value is 10k or 1k, for larger ORP12
type LDRs 10k is more appropriate. If desired the fixed resistor can
be replaced by a variable resistor so that the threshold value can be
'tuned' to different light values.
10k
A more versatile way of using the LDR is to measure a number of different light values, so
that decisions can be made at varying light levels rather than just one fixed threshold
value. A varying value is known as an 'analogue' value, rather than a digital 'on-off' value.
To measure analogue values the microcontroller must contain an 'analogue to digital
converter (ADC)' and the programming software must support use of this ADC. Most
microcontrollers only contain ADC on certain input pins, and so the input pin
connection must be carefully selected. Unfortunately with the 8 pin microcontroller in
the Chip Factory no ADC is available. To do ADc work you must use an 18 or 28 pin PIC.
The electronic circuit for using the ADC is a potential divider identical to the circuit
above. The analogue 'measurement' is carried out within the microcontroller itself.
Testing the LDR (digital)
After connecting the LDR it can be tested as a digital switch by a simple program like
this:
00
01
02
03
04
05
06
if
1 on goto 03
goto 00
high
0
wait 020
low
0
goto
00
‘ jump if the input is on
‘ else loop back around
‘
‘
‘
‘
switch output 0 on
wait 2 seconds
switch output 0 off
jump back to start
This program will switch output 0 on and off according to the light level.
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18
SECTION 3 - THE ALARM PCB
The Alarm project uses a PICAXE-08 microcontroller with an LED and piezo sounder as
user feedback devices, and a user selectable ‘output’ device (e.g. siren or strobe light).
INPUT
PROCESS
OUTPUT
digital
output
microcontroller
analogue
LED
piezo
The project can also react to digital and/or analogue sensors (e.g. an LDR light sensor).
.
The electronic block diagram is shown below.
output - 0 is connected to the LED
output - 2 is connected to the piezo sounder
output - 3 controls the output devices
input - 1 is connected to the LDR
input - 0 is connected to the push switch
Remember not to confuse the chip ‘leg’ number with the input/output pin number!
Circuit Diagram
The circuit diagram for the alarm project is shown below:
digital
input
1
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10k
10k
in0
2
4
3
PIC12F629
in1
7
out3
+
1N4001
analogue
input
100 uF
4.5V
output
device
1k
out0
330R
5
out2
BC548B
8
0V
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CHIP FACTORY ALARM PROJECT
19
BUILDING THE ALARM PCB
What you will need:
R1 and R2
10k resistor
(brown black orange gold)
R3
not used - use a wire link instead
R4
330R resistor
(orange orange brown gold)
R5
1k resistor
(brown black red gold)
R6
1k/10k resistor
(brown black red/orange gold)
(the value of R6 depends on the type of LDR used)
LED1
5mm red LED
PZ
piezo sounder
TR1
BC548B Transistor
D1
1N4001 diode
C1
100uF electrolytic capacitor
IC1
8 pin IC socket
IC1
PIC12F629 microcontroller
CT1
(not used)
BT1
battery clip
BT1
4.5V (3xAA) battery box
PCB
printed circuit board
wires and sensors (e.g. switch and LDR)
output device (e.g. buzzer or motor)
Resistor colour codes
Tools:
soldering iron and solder
side cutters
Black
0
0
Black x1
Silver ±10%
Brown
1
1
Brown x10
Gold ±5%
Red
2
2
Red x100
Orange
3
3
Orange x1000
Yellow
4
4
Yellow x10,000
Green
5
5
Green x100,000
Blue
6
6
Blue x1,000,000
Violet
7
7
Example shown:
Grey
8
8
blue, grey, brown, gold
White
9
9
= 680R ±5%
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CHIP FACTORY ALARM PROJECT
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Soldering the PCB.
The printed circuit board (PCB) is specially manufactured with a ‘solder resist’ layer to
make it simpler to solder. This is the green ‘lacquer’ layer that covers the tracks so that the
solder does not stick to these tracks. However for successful assembly the PCB must be
carefully assembled and soldered.
When soldering always make sure the solder iron tip is hot and clean. To test if it is hot
enough try to melt a piece of solder on the tip. The solder should melt almost instantly.
Then clean off the melted solder by wiping the tip on a damp sponge.
Remember that solder will only ‘stick’ to hot surfaces. Therefore never melt the solder on
the soldering iron tip and then try to ‘drop’ it onto the joint – this won’t work as the
joint will be cold and so the solder won’t stick.
To successfully solder you must hold the soldering iron in one hand and the solder in the
other. Therefore make sure the board is held on the table so it won’t move (e.g. use a
bulldog clip or get someone else to hold it for you).
Steps to soldering:
1) Clean the soldering iron tip on the damp sponge
2) Press the soldering iron tip against the pad on the PCB AND the leg of the
component. Count to 3 to give the joint time to warm up.
3) Keep the soldering iron in position and touch the solder against the joint. Allow
enough solder to melt to cover the joint.
4) Take the solder away first, then the soldering iron
5) Allow the solder to cool for about 5 seconds before trying to move the board.
After each joint is made make sure it does not accidentally ‘bridge’ across to other joints.
However be aware that some solder joints (e.g. on the two sides of the PICAXE download
socket) have two wires very close together that are already connected by a track (line) on
the PCB. In this case it does not matter if the solder joins together.
Tips!
1) Always start with the smallest components like the resistors. Then move onto larger
components like the IC socket and then finish with the tall components like
capacitors and transistors. Do not try to put all the components in position at once,
only do two or three at a time.
2) Always make sure that the components lie flat on the board before they are soldered.
When using components with long legs like resistors and LEDs, bend the legs so that
the component is held firmly in position before soldering.
3) Make sure the PICAXE stereo download socket ‘snaps’ into position flat on the board
before it is soldered (if used).
4) Make sure that the components that only work one way around (LEDs, diodes,
transistors and capacitors) are correctly aligned before soldering (see the marks on
the PCB).
5) Piezo sounder wires are very thin. Make sure you do not overheat them or they may
melt.
6) Always thread the battery snap wires down and up through the two thread holes
before soldering. This helps make a much stronger joint which is less likely to snap
off.
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CHIP FACTORY ALARM PROJECT
21
OUTPUT
ORDER: AXE102
These instructions presume you are soldering all the components directly on the board. The
instructions are identical if you are using longer wires to join some components (e.g. the LED),
although you must be even more careful you get the wires around the correct way on the LED.
revolution
V+ 0V
Notes:
ANA
DIG
PX
alarm
CF
INPUTS
WWW.REV-ED.CO.UK
1
the 22k resistor by the word ‘Revolution’ is replaced by a wire link
the resistor at the bottom of the board may be 1k or 10k depending on the type
of miniature lDR used (if in doubt use a 10k resistor)
1) Place the 1k (brown black red gold) resistor in position. The bottom resistor marked
1k may be a 1k or 10k resistor depnding on the type of analogue sensor (LDR) used.
Bend the legs to hold the resistors in position and then solder.
2) Place the two 10k (brown black orange gold) and 330 (orange orange brown gold)
resistors in position. Bend the legs to hold the resistors in position and then solder.
3) Using an off cut resistor leg, make a wire loop over the letters CF marked beside the
330R resistors. Solder in position. (Ignore the hole above the holes marked PX). Use
a second wire link in the 22k resistor position.
4) Solder the 1N4001 diode is position D1, making sure the silver bar is pointing
towards the right hand side of the PCB.
5) Push the IC socket into position. Make sure the notch at one end points up towards
the socket. Fold the legs over to hold the socket in position and then solder.
6) Solder the LED into position (or wires if the LED is to be connected by longer wires).
Make sure the flat on one side of the LED aligns with the flat marked on the PCB.
7) Solder the BC548B transistor in position, making sure the flat side aligns with the
marking on the PCB.
8) Solder the 100uF capacitor is position, making sure the + and – legs are around the
correct way.
9) Thread the battery clip down through the large hole by the letters DER. Thread it back
up through the large hole by the letters ORD. Then solder the black wire in the hole
marked 0V and the red wire in the hole marked V+.
10) Use a sticky pad to stick the piezo sounder (brass side) to the top of the PCB. Thread
the wires down through the hole below LED1 and back up through the hole marked
PZ. Solder the red wire into the bottom hole and the black wire into the top hole. It
does not matter if the red wire solder joint joins pin5 of the IC socket as they are
supposed to join anyway. The black wire should NOT join pin 6 of the IC socket.
12) Solder wires to the OUTPUT, DIG & ANA INPUT connections.
13) Carefully check the board to make sure there are no missed joints or accidental solder
bridges.
14) Insert the microcontroller into the socket, ensuring pin1 faces up.
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CHIP FACTORY ALARM PROJECT
22
Testing your circuit.
Step 1 – Check the solder joints.
Check that all the joints are connected to both the pad and the wire, and that the wire is
held firmly so that it does not ‘wobble’ when pulled. Also check that the solder does not
accidentally bridge between two pads. This is most likely to happen on the LED and on
the piezo.
Step 2 - Check the components.
1) Check that the black battery clip wire is in the hole marked ‘0V’ and the red battery
clip wire is in the hole marked ‘V+’
2) Check that the PIC12F629 chip is in the socket correctly, with the dent (showing
pin1) facing up.
3) Check that the flat edge of the LED is connected to the correct hole on the PCB.
4) Make sure you have not forgotten the wire link over the holes marked PX at the
bottom left of the board.
5) Make sure the brass side of the piezo is stuck down with a sticky pad.
Step 3 - Connect the battery.
Check the 3 AA batteries are in the battery box correctly. Connect the battery box to the
battery snap and put your finger on the PIC chip. If it starts to get hot remove the battery
box immediately as there is a problem – most likely that the chip or the battery snap
wires are around the wrong way.
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CHIP FACTORY ALARM PROJECT
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start
Step 4 – Download a program to test LED 0.
Type in and program the following program:
00
01
02
03
04
high
0
wait 010
low
0
wait 010
goto 00
high 0
wait 1
low 0
wait 1
The LED should flicker as the program downloads. After the
download is complete the LED should flash on and off
every second. If the LED does not flash check that it is
around the correct way and that the 330R resistors are in the correct positions on the
PCB.
If the program does not run check that the 22k, 10k and IC socket are all soldered
correctly. Use a multimeter to make sure you are getting 4.5V across the top legs (1 and
8) of the microcontroller.
Step 5 – Test the output
Connect an output device (e.g. buzzer) to the output wires and then type in and
download the following program:
00
01
02
03
04
low
3
wait 010
high
3
wait 010
goto 00
The buzzer should sound on and off every second. If it does not check that the transistor
and diode and buzzer wires are all around the correct way.
Step 6 – Test the piezo
Type in and download the following program:
00
01
02
03
04
beep
beep
beep
beep
goto
065
078
088
119
00
The piezo should make 4 different noises. If it does not make sure the wires are correctly
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© copyright 2002 - AXE102CF Alarm Student Project Notes Version 1.1
23
CHIP FACTORY ALARM PROJECT
24
soldered, that it is stuck on the brass side with a sticky pad (it will not work if ‘hanging
loose’) and that the wire link over the letters CF is on the board.
Step 7 – Test the switch
Connect a switch to the digital input.
Type in and program the following program.
00
01
02
03
04
05
06
if
0 on goto 03
goto 00
high
0
wait 020
low
0
goto
00
‘ jump if the input is on
‘ else loop back around
‘
‘
‘
‘
switch output 0 on
wait 2 seconds
switch output 0 off
jump back to start
The LED on output 0 should light whenever the switch is pushed. If it does not check
that the switch and 10k resistors are correctly soldered.
Step 8 – Test the LDR
Connect an LDR to the second input. Type in and program the following program.
00
01
02
03
04
05
06
if
0 on goto 03
goto 00
high
0
wait 020
low
0
goto
00
‘ jump if the input is on
‘ else loop back around
‘
‘
‘
‘
switch output 0 on
wait 2 seconds
switch output 0 off
jump back to start
The LED output should come on at different times as you raise and lower your hand over
the LDR (so that different amounts of light fall on the LDR). If they do not check that the
LDR and 10k resistor are correctly soldered.
If all these tests pass, you can be congratulated as you have correctly built and
assembled your alarm! It is now time to develop and test your own program to
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© copyright 2002 - AXE102CF Alarm Student Project Notes Version 1.1
24
CHIP FACTORY ALARM PROJECT
25
operate your alarm system.
SECTION 4 - PROGRAM IDEAS.
Now that you have assembled and tested your alarm, it is time to develop your own
program. This program can make the alarm react in different ways to the digital and
analogue sensors.
Included on the next page is an example program. This is designed to give you a starting
point for your program. You may choose to modify it or to start a completely new
program if you prefer.
Program Explanation
This general purpose program has a main loop which flashes the LED on and off, and
also checks the analogue sensor (fitted with a LDR) and digital input (fitted with a
switch). When the push switch is pressed an alarm is sounded for two seconds.
If the LDR light sensor is covered the piezo will make a awarning beep sound until the
light level rises again.
Program
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
low
3
high
0
if 1 off goto 20
if 0 on goto 13
wait 005
low
0
if 1 off goto 20
if 0 on goto 13
wait 005
goto 00
high
3
wait 020
low
3
goto 00
low
3
beep 050
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© copyright 2002 - AXE102CF Alarm Student Project Notes Version 1.1
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CHIP FACTORY ALARM PROJECT
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22
23
if 1 on
goto
goto
00
20
ACKNOWLEDGEMENT
This project development was funded by the UK
Offshore Oil and Gas Industry.
www.oilandgas.org.uk/education/
The Chip Factory is endorsed by the
Technology Enhancement Programme
www.tep.org.uk
(c) Revolution Education Ltd 2002
www.rev-ed.co.uk
All rights reserved.
May be photocopied for non-commercial educational
use in classrooms in schools and colleges only.
PICAXE is a trademark of Revolution Education Ltd
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