Using a 4046 PLL we found this circuit in the December 1989 issue of Radio Electronics magazine. The circuit operates at 220kHz, but this frequency can be changed by changing C3.
This circuit triggers a relay when the phone rings. An application is like remote doorbell. The circuit...
This simple CMOS circuit generates two-frequency signals for use as a signal injector. The circuit...
With a mains-rated transformer and 1:1 winding this benchtop circuit was found in the January 1995...