This simple circuit for headphones or small speakers was found in documentation from the 90s. The circuit works with voltages from 5 to 9 V and has good gain.
This circuit is like the previous one except that it can be triggered electronically. The circuit is...
Found in 90s Radio Electronics, this audio indicator makes use of an integrated circuit that is...
Found in the October 1992 Radio Electronics magazine, this oscillator is controlled by switch S1....