This circuit was found I a 1965 Radio Schack documentation. The transistors are from that time, admitting equivalents. The transformer has 500 ohm primary and secondary depending on the speaker.
Activating a relay from pulses (from a monostable, for example) can be useful in many types of...
This project uses an unusual integrated circuit that consists of a programmed timer. The circuit was...
I found this circuit in a Popular Electronics from 1992. The circuit shows how we can receive...