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 proximity relay circuit was found in the July 1990 Radio Electronics magazine. The supply...
This circuit is from an old operational amplifiers manual. However, the setting applies to modern...
Using an operational amplifier, the figure shows how to convert the waveform to low frequency...