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.
This hearing aid or stethoscope headset amplifier was found in a 1980s documentation. The...
Found in Popular Electronics from the 90s, this circuit can generate signals from 1 to 10 MHz...
Based on the 555, this circuit was obtained from Internet documentation, serving to generate a...