Did you ever try to make a telephone call on a campsite by using the tent pegs of your tent? Well, here's how you can do it.
This simple electronic circuit is a telephone set that uses only one wire to connect two or more posts. The other wire, the ground return, is not needed. In fact, the ground itself is literally used as the second wire. You simply connect the telephone to the (metal) pegs of your tent and to this single wire. Is the signal not loud enough? Add a little water to the ground around the tent peg and you will get a better reception.
Does it sound unbelievable? This circuit can transmit and receive signals sent through a material that offers a high resistance to electric current, e.g. the ground. It will not operate on dry sand or rock, but clay, water and agricultural land perform quite well. It will even operate on two different human lines, made by several people joining hands. If it doesn't at the first try, wet your hands. This lowers the resistance.
You can connect two or more telephone sets to the same single wire. Only one of them can "transmit", whilst the others listen. In a way, it works just like radio communication.
The circuit itself consists of an operational amplifier uA741, two switches, an earphone of a normal telephone set (100 - 400 ohm impedance), a 9-volt battery and a few other components. Switch S1 needs to be of the push-to-talk type. Since the circuit is not critical, it can be soldered together without using a printed circuit board.
WARNING
NEVER use an electric fence to connect the intercoms - this will damage the circuit and is also very dangerous.
Created on 2004-10-03 21:39:09 by webmanager
Updated on 2005-01-21 22:33:23 by webmanager
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