This circuit is from an American 1964 documentation. Transistors of the time are used, but modern equivalents can be employed.
This circuit is based on the light comparison of two LDR sensors. We found it in a 90s Popular...
We found this crystal AM radio using a germanium diode in a Japanese magazine in 1967. The circuit...
When a model train crosses a level crossing, interrupting the light on the sensor, this circuit...