This circuit, from the 70's, can be assembled with a more modern FET like the BF245. The circuit is powered by a 9 V battery, as its consumption is very low.
Found in a 1968 US publication, this circuit is designed to measure very weak signals. The...
The sensor can be made using two bare wire or two screen with a piece of tisse between them. One...
This circuit serves as a binary demonstrator using 3 LEDs. The circuit can be scaled up for a...