This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This circuit came out in a publication called Electronics Handbook of 1993. The circuit shows how...
Found in documentation from the 1980s, this circuit makes use of general-purpose diodes and...
This circuit memorizes through an LED indicator if your phone was used during your absence. The...