Found in Popular Electronics from the 90s, this circuit uses a reed switch on the rails as a sensor. Instead of lamps, in a modern version, LEDs can be used.
This circuit was found in a 1970s General Electric documentation. This circuit already used an...
A rectangular signal can be generated with the figure setting. The values given in the circle...
This circuit was obtained in an old publication. The FET can also be the BF245. The potentiometers can be...