This circuit triggers a Sonalarme when the LED used as a sensor receives light. The circuit was found in an old documentation, but the components used are all current.
The figure shows how to use an LM3914 with a variable range moving point. The circuit has an...
This circuit was found in a 90s Popular Electronics. It uses a varicap that admits equivalents. The...
This circuit is from an Electronics Now from 1998 and can be easily assembled with other JFET...