In the figure we have a good rectangular signals generator with several frequency bands. The circuit is based on old logic but can be implemented with modern equivalents.
This source of constant current was obtained in an American documentation of 1973. The transistors can be...
When light fails to focus on the sensor, a common photo-transistor, the relay closes its contacts....
This low impedance circuit was found in an Electronic Design from the 90's. Operational amplifiers admit...