Poptronics recommends this circuit for use in the car when the headlights are left on. The circuit uses a sensitive relay with contact current according to the headlights.
Placed in the vicinity of a telegraphic transmitter (CW), this circuit produces an audible signal on...
Damped oscillators can be used to produce sound from percussion instruments such as the triangle, bell,...
We found this circuit in a 1983 English magazine, but it can be easily assembled with the BC548...