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Measuring RPM via Photo reflector
Computer
Interface
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This will result in VL > VR, which in turn makes the output of comparator 2 high (pin 7 becomes ~9V). As a result, the Left Motor stops but also, since the output of the comparator 1 goes low, the Right Motor rotates. So the robot will turn to left and find the dark line again. The resulting motion is a zig-zag around the dark line. C. Amplification Section: This section (See Figure 4) is made of two amplifier subsections. One, consisting of transistors TR1 and TR3, connects pin 7 of the the second comparator to the Left Motor. The second, consisting of transistors TR2 and TR4, connects pin 1 of the first comparator to the Right Motor. Let us see how one of these, the first, operates. If the output of pin 7 is high (~9V), very little current will flow through the 68k resistor connected to the BASE of TR1. Therefore this transistor acts as a switch which is turned off. As a result very little current will leave the COLLECTOR of TR1 which is in turn connected (through the 750W resistor) to the BASE of TR3. In turn, very little current will leave the COLLECTOR of TR3 (no amplification). Since the collector of TR3 is connected to the Left Motor, it does not rotate. The opposite is true when pin 7 is low. To summarize: Pin 7 high Left Motor stopped D. Power Source There are two sources of power. A 9V battery provides power for the electronic circuits and two 1.5V cells in series power the motors. In the lab, you will use the 0 to 25V variable power supply set for 9V, and the 0 t0 6V variable supply set to 3V
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