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　　Photoelectric encoder signal is converted by the output shaft of the electric light and the amount of displacement of the machine geometry and converted to pulse or digital sensors, is now the most widely used sensors, optical encoder device is a grating disk and the photodetector means bound, in the photoelectric encoder, it has its unique application circuit, it has a good performance in measuring angles, measuring the distance when you can have a strong anti-jamming capability, but also has given it a stable pulse signal, therefore, the pulse signal after statistics can later be converted into digital signals for measurement.
Many car driving simulator can also use optical encoder as a sensor, which can measure the angle of rotation of the steering wheel, it is a collection of open collector output circuit type, a certain degree of output resolution, due to the car's steering wheel in both directions, clockwise and can be rotated counterclockwise, count required before the output signal of the encoder identify its phase.
　　When the optical encoder clockwise channel A leads channel B output waveform of the output waveform 90, D flip-flop output Q (waveform W1) is high, Q (waveform W2) is low, the above NAND gate open , by counting pulses (W3 of the waveform), the pulse applied to the input of the bidirectional counter in the CU 74LS193, counting with the addition; in this case, following the NAND gate closed, its output is high (waveform W4). When the counter-clockwise optical encoder, channel A Channel B output waveform of the output waveform delay than 90 °, D flip-flop output Q (waveform W1) is low, Q (waveform W2) is high above the NAND gate off, its output is high (W3 of the waveform); in this case, the following NAND gate opening, by counting pulses (W4 of the waveform), to the input of the pulse counter is decremented by bidirectional CD 74LS193, and counted in a subtraction method.
　　When the steering wheel is rotated clockwise and counterclockwise, the maximum rotation angles are twice and a half, use a resolution of 360 pulses / turn encoders, the maximum number of output pulses is 900; the actual use of the counting circuit with 3 output so that when the steering wheel is rotated clockwise, counter circuit; chip 74LS193 composition, power initialized on system, the first of its reset (CLR signal), then its initial value is set to 800H, ie 2048 (LD signal) in the range of 2048 - 2948, when the steering wheel is rotated counter-clockwise, counter circuit output in the range of 2048 - 1148; data counting circuit output D0 ~ D11 to the data processing circuit.
　　When we actually use the encoder, the steering wheel frequently and counterclockwise rotation clockwise, because there are errors in some details, after working for some time, the circuit output count when the steering wheel is not back in 2048, but there are several digital deviation; to resolve this error, we give the encoder adds a steering wheel gyrus detection circuit through the system after processing, in the case of data simulator is not running, the system has detected gyrus circuit, data steering wheel back in the state, and the output of the counter circuit is not 2048, counting circuit can be reset and re-set the initial value.