Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.
We found this circuit in a Radio Electronics from October 1963. The circuit uses an output...
This circuit from an American documentation from the 70s, indicates a photodiode to generate...
This circuit uses components that are still common despite being from 1995 documentation. The circuit can...