Found a documentation on PCs from 1996, this circuit can be used as a shield. The relay is rated at 100 mA of coil current.
This circuit was found in the March 1980 issue of Radio Electronics magazine. It is based on the...
This circuit (2009) has driver control through the RTS signal or in automatic mode through the...
This monotone alarm oscillator circuit was found in July 1975 Radio Electronics magazine. Power is...