Photoelectric encoder application circuit！

A photoelectric encoder is a sensor that converts the amount of mechanical geometric displacement on an output shaft into a pulse or digital quantity by photoelectric conversion.

Photoelectric coding has good performance, strong anti-interference ability when measuring angle and displacement, and has stable and reliable output pulse signal, and the pulse signal can be counted to obtain the measured digital signal. Therefore, when developing the car driving simulator, we use the photoelectric encoder as the sensor for the measurement of the steering angle of the steering wheel. The output circuit adopts the open collector type, and the output resolution is 360 pulses/circle. Considering that the steering wheel of the car is two-way. It can be rotated clockwise or counterclockwise. It is necessary to phase the output signal of the encoder before counting. The phase-detection and bi-directional counting circuit actually used by the photoelectric encoder is given. The phase-detecting circuit is composed of one D-flip-flop and two NAND gates, and the counting circuit is composed of three 74LS193.

When the photoelectric encoder rotates clockwise, the channel A output waveform leads the channel B output waveform by 90°, the D flip-flop output Q (waveform W1) is high, Q (waveform W2) is low, and the upper NAND gate is open. The counting pulse passes (waveform W3) and is sent to the pulse input terminal CU of the bidirectional counter 74LS193 for addition counting; at this time, the lower NAND gate is closed, and its output is high level (waveform W4). When the photoelectric encoder rotates counterclockwise, the channel A output waveform is delayed by 90° than the channel B output waveform, the D flip-flop output Q (waveform W1) is low, and Q (waveform W2) is high, and the upper NAND gate Closed, its output is high (waveform W3); at this time, the lower NAND gate is opened, the counting pulse passes (waveform W4), and is sent to the decrementing input terminal CD of the bidirectional counter 74LS193 for subtraction counting.

When the steering wheel of the car rotates clockwise and counterclockwise, the maximum rotation angle is two and a half. The encoder with a resolution of 360 pulses/turn is used, and the maximum number of output pulses is 900. The actual counting circuit uses 3 pieces. 74LS193 component, when the system is powered on, it is reset (CLR signal), and its initial value is set to 800H, which is 2048 (LD signal); thus, when the steering wheel rotates clockwise, the output range of the counting circuit For 2048 ~ 2948, when the steering wheel rotates counterclockwise, the output range of the counting circuit is 2048 ~ 1148; the data output D0 ~ D11 of the counting circuit is sent to the data processing circuit.

In actual use, the steering wheel frequently rotates clockwise and counterclockwise. Due to the quantization error, after a long period of operation, the output of the counting circuit may not be 2048 when the steering wheel is returned, but there are deviations of several words; A problem, adding a steering wheel back detection circuit, after the system works, the data processing circuit is in the non-manipulation state of the simulator, the system detects the return detection circuit, if the steering wheel is in the return state, and the data output of the counting circuit is not 2048 , the counting circuit can be reset and the initial value can be reset.

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