In this circuit of an American documentation of the 90s, when the light is cut, we have the production of a pulsating tone. R3 determines the trigger sensitivity.
This partial circuit that must be added to a preamplifier output transistor as in CB19186E...
This 4-competitor TTL speed game was obtained in a 1980s documentation, but can still be easily...
We find this circuit in an American publication of 1978. The integrated circuit is the CMOS 4013...