This sonic control circuit for a small robot turtle was obtained in an American documentation from 1967. The circuit uses a ceramic capsule to fire an SCR.
This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply...
This circuit was found in a Popular Electronics from the 90s. The frequency depends on the...
This circuit can be used as an answering password system in a store, office, or other location....