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Measuring RPM via Photo reflector
Computer
Interface
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Line Tracking Robot Project ( uC less ), by Sohrab Rabii and Siddharth Deliwala Each group of three students is provided with one kit. However, to make the project more meaningful, each group will construct and test each of the electrical subsystems of the robot on a breadboard and test it. After the entire system is put together in this fashion and its operation understood, each group will also put the pre-wired kit together and observe its behavior. Each robot has the following subsections: A. Sensor Section A. Sensor Section The sensing subsystem consists of two identical parts called Photo Interrupters. Each photo interrupters is made of a light emitting diode (LED) and a phototransistor. The LED emits infrared radiation. If the Photo Interrupter passes over a white surface, the infrared light is reflected back and is detected by the phototransistor. Let us assume that this is the case for the right (shown in red) photo interrupter assembly. The result is that the emitter-collector resistance drops and a large current flows through the red 27kW resistor. This created a large voltage drop across this resistor and VR is reduced to near zero. If at the same time, the left photo interrupter assembly (shown in blue) is over the black line, the radiation is not reflected back to the phototransistor and the emitter-collector resistance remains high. This results in a small current through the blue 27kW resistor. The resulting small voltage drop across this resistor leads to a high value of ~9 V for VL. We send these two voltages to a comparator, which then makes one of the two wheels of the robot rotate in such a fashion that it turns to the left. The 10kW resistor is a potentiometer, and we adjust it so that when light strikes both photo-interrupters (or neither of them), the left motor will be rotating and the right motor stopped. We use the pre-assembled photo-interrupter units from the kit.
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