The main feature of this circuit found in an old American publication is that it is powered by the very signal it converts. The transistors are of the time and can be replaced by current types.
This circuit uses a Hall device from that time as a sensor. The circuit is from an English...
Found in Radio Electronics from the 90s, this siren finds many variations on this site. The...
This audio generator that produces both rectangular and sinusoidal signals was found in a...