This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit is based on a 555 and a MOSFET consisting of a flasher that controls a buzzer.
When S1 is pressed, the circuit allows music to be played from an audio source on the telephone line....
This simple window comparator based on the well-known LM339 was found in the June 1998 issue of...
This circuit produces a voltage drop in the first pulse, turning off the relay. On the second...