This sensitive circuit was found in the June 1995 Electronics Now magazine. R1 can be from 10k to 1M depending on the desired sensitivity. Power is supplied by the relay.
The circuit in the figure is from a source with the possibility to adjust the output voltage from...
We found this circuit in an old magazine 73 of 1974. The circuit must be powered by a continuous voltage...
This circuit is from a 1987 American publication called Electronics Handbook. The circuit can be...