This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
We found this inverter in a Popular Electronics from the 1980s. The output is not perfectly...
Found in American documentation from the 90s, this circuit uses common FETs. It has a range drift...
The frequency of the sound produced in the speaker depends on the light that falls on the...