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 is yet another version of the light-controlled oscillator that can be found on this website. This...
Originally created to feed the filaments of a 12AX7 as an audio preamplifier to eliminate the...
The incidence of light in the LDR causes this circuit to start operating, emitting a sound whose...