We found this circuit in the July 1969 Radio Electronics magazine. The circuit uses a coupler made with a lamp and an LDR. The power of the lamp determines the types of diodes.
In this circuit, D.A. which is actually O. A. of an operational amplifier, which can be any type...
Found in a Maxim publication from the 90s, this circuit generates signals from 10 to 25 kHz with a...
This circuit uses a resonant reed switch at the trigger frequency. The circuit is from General...