This 1967 modeling circuit mimics the whistle of a locomotive. The steam-shrieking wheezing is set in a 2k2 potentiometer.
This circuit controls a relay from the light incident on a sensor. The sensor is an LDR and the...
This 2003 circuit is powered by the telephone line itself. Its purpose is to notify you when there...
Originally this circuit is from an English magazine, but I found it in Argentina's Radio Chassis...