Photoelectric conversion counting circuit

(1) Circuit working principle When counting beer bottles on the conveyor belt, the running glass bottles should first be converted into pulse signals, and then
the pulse signals (each bottle generates a pulse) are sent to the counter for automatic counting. The circuit shown in Figure 9-32 is a photoelectric conversion
circuit for a glass bottle counter .     When there are no glass bottles on the conveyor belt, the 3DU photosensitive transistor has low resistance when exposed to direct light, the photocurrent is very large, and VTI is cut off. At this time, VT2 is saturated and VT3 is cut off. At the moment when the glass bottle blocks light, the phototransistor shows high resistance, fs increases, VT1 is saturated, and Vrl drops from +5-v to ov. This negative jump is differentiated by RC to obtain a negative pulse, which triggers the monostable circuit, causing VT2 to cut off and VT3 to turn on. The monostable circuit automatically returns to its original state after a period of time and obtains a wider pulse, which avoids the phenomenon of multiple signals caused by one bottle due to flash, etc.     D1 ~ D5 form an integral shaping circuit, which is also a monostable circuit. It can narrow the above-mentioned wider pulses to meet the counting requirements.     Because the glass bottle is transparent, the photocurrent and dark current of the phototransistor change within a small range. In order to reliably saturate and cut off VT1, the potentiometer RP can be adjusted carefully and repeatedly. ． (2) When selecting components for VTl ~ VT3, choose 3DG6, p≥so resistant tubes. D1～ D5 select 74LSOO type "NAND" gate integrated circuit . The values ​​of R and Rd should be determined according to the shading time of each bottle , which can be calculated as CR -2￡ (f is the shading ratio).