We found this circuit in a 1968 Electronics World. It fires a buzzer if the ignition key is turned on and the headlight is off. The circuit uses an included oscillator buzzer like the Sonalert.
This circuit is na analog display of LEDs, operating from a voltage signal applied to mits input....
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...
This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio...