This interesting benchtop circuit was found in the May 1977 issue of Radio Electronics magazine. The circuit has frequency adjustment, and the waveform selected by a switch.
In the figure we have the way to use a stepper motor as an encoder. Operational amplifiers can be of...
Placed inside the refrigerator, this circuit triggers an oscillator when the part is opened...
We found this circuit in an old documentation from the 70s, but it can be assembled with more...