Two sensors are used in this simple remote-control circuit, one to switch on and one to switch off the relay. The circuit is from 1986 documentation. The transformer has 12 V of secondary.
With this circuit it is possible to obtain an input resistance of 100Gohms for a multimeter, with...
This amplifier, to detect biological signals in implanted transmitters, uses transistors such as...
This application is not modern since few computers have parallel ports. But you can use this...