This circuit was found in a Popular Electronics from the 90s. The circuit has temperature compensation. Coil and capacitors depend on the frequency at which the circuit will be used.
Found in a Hands On Electronics from the 80's, this circuit activates a relay with alternating...
The frequency of this circuit, that makes use of a tunnel diode as an active element, depends on...
Found in 1980s Electronic Engineering, this circuit uses common phototransistors as sensors. The...