This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based on a 741 that activates a buzzer with oscillator. R5 adjusts the sensitivity.
Using a 741 op-amp this circuit high-pass to 10 kHz was found in the February 1995 issue of...
This circuit produces an intermittent ring tone being triggered directly by the telephone line. However,...
This two-port configuration of the 4001 was found in the April 1988 issue of Radio Electronics magazine....