The circuit in the figure is suggested by Texas Instruments in its optoelectronics manual and consists of a sensor for objects passing on an assembly line conveyor belt. This circuit uses a phototransistor to detect the passage of the object, which generates a logic transition in a 7414-type trigger gate. This transition is used to trigger a TTL monostable, which generates a counting or control pulse of constant duration on output pin 6. The duration of this pulse depends on the 15k ohm resistor and the 10 nF capacitor, components that can be changed depending on the desired application.
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