This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is not an easy component to obtain and the power can be supplied with a single button cell.
This circuit synthesizes the tick of a metronome with the speed controlled in RV1. The circuit is...
This circuit sensor is an NTC with a resistance of the order of 2k. The SCR can be from the TIC...
This circuit generates approximately 30 Hz signals from a 3.3 kHz clock. The circuit was found at...