This circuit, based on a 555, was found in a Popular Electronics from the 90s. The circuit has the frequency determined by R1, R2 and C1.
If you are on an old PC that you use for experiments, control or other applications, this circuit is...
We found this circuit in an American publication from 1977. The circuit drives two LEDs according to...
In this circuit, the integrated amplifier used is uncommon today. The circuit is from an American...