Analog control unit for mobile robots

Analog control unit for mobile robots
Analog control unit for mobile robots
 Soldering kit for experimentation
 For Fischertechnik robots and others
 Most diverse functions
 Requires no programming
 Patented sensor technology
Summary
We are pleased that you have decided for this
high-quality soldering kit for mobile robots. It
opens up a new and exciting access to analog
amplifier circuits. You will certainly have fun
and experience various possibilities to
experiment and tinker about for a long time.
This control unit gains its “sensory impressions”
with the help of light sensitive sensors. With the
patented combination of sensors, your robot can
navigate precisely and react sensitively to its
environment.
The “brain cells” of the circuit board consist of
four operational amplifiers. They control the
motors and can be wired variably with resistors,
capacitors, or diodes via numerous slots.
Components overview
The unit is capable of a lot:

Surprising driving maneuvers through
sensitive reaction to light and shadow

Avoiding obstacles and collisions

Following dark or bright lines

Following different objects

Remote controlling via flashlight

Interaction with
infrared light

Combination of different functions
other
robots
via
Note:
IC1 includes the two operational amplifiers OP1R and OP1L (triangular circuit symbols). IC2 includes
OP2R and OP2L. In this application each motor is controlled by two operational amplifiers.
4. Insert two 3-pin and two 2-pin sockets at the
indicated locations on the back of the board
and solder them on the top.
5. The 5 photo transistors (light sensors) have a
transparent housing with a red marker and
legs of different lengths. The curved lenses
must be looking outward. Solder three of
these photo transistors T1, T3, and T5 at the
corresponding markings.
6. Solder the wires for the power supply and the
motors on the back of the board. Pay
attention to correct polarity.
Note:
To move forward, the voltage at MR1 (red plug)
has to be higher than at MR2 (green plug) and
the voltage at ML1 (green) has to be lower
than at ML2 (red).
Preparation and first commissioning
1. Build your Fischertechnik bot e.g. as shown in
the picture or use a different robot platform.
Adapt your Mini Bot in order to fix the control
unit. Connect the plugs for the motors.
2. Shorten the pins of the remaining two photo
transistors T2 and T4 (red marking) according
to the illustration. Solder a piece of wire to
each of them. Pay attention to correct
polarity (C -> red / E -> green). Solder the
other end of the wires to a 2-pin socket.
Finally plug these sockets into the 3-pin sockets
of the control board ensuring that the contacts
located towards the center of the board remain
free and that the curved lenses of the sensors
are directed forward. When installing the
sensors, the contacts must not touch.
Alternatively you can use the photo transistors
from fischertechnik.
7. The test circuit shown in the illustration
allows you to adjust the maximum speed of
the motors via a series resistor if necessary.
For this adjustment, the operational
amplifiers OP1R and OP1L are set to
maximum gain. Use the 14-pin sockets to
connect the [+] and [–] inputs of the OPs
according to the illustration, each via a 1 MΩ
resistor and a 0 Ω resistance bridge to the
supply voltage (square solder pads with [+]
or [–] marking). Then use the 8-pin sockets to
connect the [+] and [–] inputs of OP2R and
OP2L, each via a 10 MΩ resistor to the supply
voltage or the output of OP1R and OP1L.
8. Initially, connect both motor connections MR1
and ML1 directly via a 0 Ω resistance bridge
with the outputs of OP1R and OP1L according
to the illustration. Now turn on your robot. If
it drives in a slight curve, replace the 0 Ω
bridge
before the faster of the two
motors with the 4.7 Ω resistor
or the 10 Ω resistor
, ensuring
the robot drives in a line as straight as
possible. The installed resistor then stays in
place for all circuits.
Note:
The right motor rotates forward if the voltage at
the [–] input of OP1R is lower than at the [+]
input. The left motor, however, rotates forward
if the voltage at the [–] input of OP1L is higher
than at the [+] input. OP2R and OP2L invert the
output signals of OP1R and OP1L to let the
motors rotate in both directions with full speed.
Short introduction to the operational amplifier
An operational amplifier (OP) has a [–] input, a
[+] input, an output, as well as two connections
[+/–] for the power supply.
It amplifies the voltage difference between the
[+] input and the [–] input. However, as this
amplification is far too high for most
applications, a resistor R1 is installed before the
[–] input and the output signal Out is returned to
the [–] input via another resistor R2.
Via this feedback, the amplifier controls the
output Out to align the voltage at the [–] input
with the voltage at the [+] input.
The supply voltage in the diagram is U = 9 V.
The signals of the circuit (In+, In–, and Out) are
displayed as voltage arrows relative to 0 V and
are connected via the red bar. For example,
input voltages In– = 6 V and In+ = 5 V result in
output voltage Out = 3 V. The horizontal position
of the arrow In+ is determined by the ratio of
the resistors R2/R1 (2MΩ/1MΩ) and determines
the amplification A, which is the ratio between
the change of Out and the change of In– or In+.
a) If e.g., In– is increased by 1 V (and In+
remains constant), Out decreases by 2 V. In this
case, this results in a negative amplification A =
–R2/R1 = –2. You will use this connection later
for “tibo as light follower”.
b) However, if In– remains constant and In+ is
increased by 1 V instead, Out increases by 3 V.
The amplification A = 1+R2/R1 = 3 is now
positive. You will use this connection for “tibo as
line follower” in the following.
Note:
For more information about the functionality of
the control unit please also read the manual of
the tibo robot kit at: variobot.com/downloads
How to build a light follower
This circuit enables your robot to navigate
autonomously with the help of the three
sensors T1, T3, and T5. The two sensor signals
InR and InL control the motors via OP1R or OP1L.
OP2R and OP2L invert these two signals after a
short delay (depending on the 220 nF
capacitors) in order to change the direction of
the motors. As the group of sensors always
responds to relative lighting conditions, the
control unit can navigate in variable lighting
without having to send out light by itself.
1. Adapt the circuit according to the wiring
diagram. (2M2 signifies 2.2 MΩ, 220n
signifies the two 220 nF capacitors). For
simple orientation, all slots are marked by
letters from A to E and numbers from 1 to 8.
Ensure that the components are connected by
the traces on the circuit board according to
the diagram.
2. Set the potentiometer P1 to center position at
5 MΩ and potentiometer P2 to left position at
0 MΩ with a small screwdriver.
3. Turn on your robot and observe how it
behaves. Adjust the relative incidence of light
on the sensors if necessary.
If the robot e.g., mostly turns to the right (the
right motor rotates backwards), the right sensor
T5 is receiving too much light. Cover T5 a little
bit. If the robot does not move forward at all
even though his path is free, screen both T1 and
T5 from the light a little more. But not too
much! Otherwise, the robot will be blind.
4. Now observe how it reacts to light and
obstacles. What roles do the brightness and
the size of the obstacles play? What influence
does the potentiometer P1 have?
If the resistance of P1 is reduced (potentiometer
turned to the left), the robot tends to move
backwards or to change direction. If P1 is
increased, it rather moves forwards and maybe
is not able to turn on the spot.
5. Test different amplifications and damping by
varying the resistors R(D7) and the capacitors
C(D8) or C(E7).
How to build a line follower
With this circuit, you can let your robot follow a
dark or bright line. The serially wired sensors T2
and T4 supply the voltage signal InM, which
controls the motors via OP1R and OP1L.
1. Adapt the control circuit according to the
wiring diagram. Set the potentiometer P2 to
left position at 0 MΩ for maximum speed.
2. Use a bright surface with consistent and
sufficiently strong lighting from above. Make
sure that no direct light influences the
sensors T2 and T4.
3. Tape a desired lane on the surface with the
black electrical tape.
4. Place the robot on the line and off it goes!
5. If the robot does not drive in the middle of
the lane, you can adjust T2 and T4. If it
drives e.g., too far on the right of the lane or
even strays from it completely, the left
sensor T2 is getting too much light. Screen it
a little from the light by shifting the red 5
mm building block above.
6. Use P2 to adjust the speed of your robot.
7. Test how the robot behaves when
confronted with lines of different widths,
intersections, or even branching.
8. Test different amplifications and damping by
varying the resistors R(A6), R(B7), R(D7), or
the capacitors C(E8).
9. The two additional 4.7 MΩ resistors R(D3)
effect a speed reduction of both motors,
when the robot has to change its direction.
Test how it works without them or change
its value.
10. Let the robot push small dark objects ahead
of him instead of letting him follow lines.
11. Place the sensors T2 and T4 on the inner
slots of the corresponding 3-pin socket to
make it follow a bright line (e.g., a strip of
paper) on a dark background.
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