Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic baths in developing rooms but can be used for other purposes. The circuit beeps at 30-second intervals.
This circuit is indicated for audio tests, the tracks being selected by the capacitors. The...
This passive circuit was found in a 1980s documentation. The circuit serves to indicate the...
This small 3 transistor transmitter was found in an English publication from 1963. The coils must...