This circuit is from a Radio Electronics from February 1959. The circuit has a speaker output and good sensitivity. Power is supplied from a 9 V battery.
In this transmitter L1 and L3 are formed by 5 turns of wire 22 and L2 and L3 by 4 turns of the...
We found this circuit in a 1983 publication. It is a simple touch alarm circuit using a SCR type...
This circuit was found in American documentation from 1966, but it can be assembled with a modern...