We found this circuit for musical instruments in the March 1992 Radio Electronics magazine. The circuit has outputs according to the desired scale from a crystal oscillator at the indicated frequency.
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...