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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