This circuit was found in an EDN from the 90s. The circuit employs a double 555 and uses the courtesy light switches of the car as sensors.
Found in a 1995 Hands On-Electronics, this circuit generates a sinusoidal signal whose frequency...
This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from...
Upon pressing the switch, the circuit generates a pulse whose duration depends on C. The...