Found in 1965 Radio Shack documentation, this circuit has a crystal phone output in the 14.8 kHz range. The coil consists of 200 turns of wire 25 in a 1.5 m side square.
In the figure we show our first circuit that consists of a simple touch switch capable of driving a...
This circuit was found in an 80's Electronic Engineering. The power supply must be symmetrical. The...
This metal detector was found in a French magazine Radio Plans from 1977. The phone can be a...