This circuit is from a 1980s Motorola documentation. The circuit can be set to fire from 60 to 120 V DC or from 42 to 84 V AC. The circuit has a forehead button that activates an indicator lamp.
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...