This circuit was found in documentation for radio amateurs of the 1980s. The circuit is intended to produce a tone for modulation in telegraphic transmissions.
We find this microphone voice effect in 1992 documentation. The vibration of the relay contacts...
This circuit for the car uses LDRs as sensors and does not need to be connected to the lamp. The...
Found in a Popular Electronics from the 90s, this circuit can be made with current equivalent...