Opto Interrupter
Opto Interrupters are commonly used in many arcade games e.g. steering
assembly in older driving games, scoring switches in Whack A Crock etc.
Uninterrupted light beam will turn the phototransistor "ON" connecting
the ground to the game board input. When the light beam is interrupted the
phototransistor turns "OFF" , the ground is disconnected from the
input and the pull-up resistor R1 forces the input to go "HIGH" (5V
level).
