The sounder consists of two small electromagnets mounted in a vertical position on a wooden base. The magnets are connected at the bottom by a strip of heavy sheet-iron which acts as a yoke.
Fig. 133.—A Simple Home-made Telegraph Sounder.
The armature is made out of sheet-iron, rolled up in the manner shown in the illustration. One end of the armature is fastened to a wooden block in such a position that the armature comes directly over the magnets and about one-eighth of an inch above them. The opposite end of the armature moves up and down for about an eighth of an inch between two screws, each fastened in a wooden block mounted on an upright board in the back of the magnets. The purpose of the screws is to make the "click" of the sounder louder and clearer than it would be if the armature only struck the wood.
A rubber band or a small wire spring passing over a screw and connected at the other end to the armature will draw the latter away from the magnets when the current is not passing.
The terminals of the magnets are connected to binding-posts mounted on the base.
Fig. 134.—A Diagram showing how to connect two Simple Telegraph Stations.
The key and sounder should be placed in series with one or two cells of a battery. Pressing the key will then cause the armature of the sounder to be drawn down and make a click. When the key is released, the armature will be drawn up by the spring or rubber band and make a second click.
Hardly a boy interested in mechanics and electricity has not at some time or other wished for a telegraph instrument with which to put up a "line" with his chum.