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 L144 operational, this circuit applies to other equivalent operational. The circuit is from...
This circuit has a gain of 34 dB and a good power to be used as an audio booster in cars. The...
The circuit shown in the figure can be implemented with more modern equivalent operating systems. We...