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 circuits below were found in amarican publication of the year 1958. The transistors are...
This circuit produces signals that depend on the input control voltage. It is a Voltage Controlled...
The bipolar transistors may be BD136 and BD136 and FET of any type for 1 A current at least. The...