This approach alarm circuit was found in the September 1970 Radio Electronics issue. The 1 mH coil is wound on a ferrite rod. The relay is 12 V sensitive.
This PWM circuit was found in an American publication from 1978. It consists of a simple control that...
This circuit, from an old ON Semiconductor publication, suggests a shield to excite an LED from an...
The integrated circuit used in this application is not currently common. The circuit is from 80s...