This indicator circuit used and game machines (arcades) to indicate that the machine is being shaken was found in NASA documentation. The circuit uses as a sensor a container with water and three sensors.
This circuit was found in an Experimenters Handbook of the 1990s. The purpose of this circuit is to...
Signals from old cordless phones can be picked up with this circuit. L1 has 10 to 20 turns of 32...
This emitter-coupled transistor LC oscillator circuit was found in the May 1970 issue of Radio...