Fig. 131.—A Typical Telegraph Sounder, showing the Various Parts.
Every time that the key is pressed, an electric current is sent out into the line. The current flows through the magnets of the sounder and causes the armature to be drawn downward. The lever strikes the anvil and produces a "click." When the key lever is released, the current is shut up and the lever flies up and clicks against the top of the anvil.
The period of time between the first click and the second click may be varied at will according to the length of time that the key is held down. A short period is called a dot and a long period a dash. Combinations of dots, dashes, and spaces arranged according to the Morse Alphabet, make intelligible signals.
How To Make a Simple Key and Sounder
The little telegraph instruments shown in Figures 132 and 133 are not practical for long lines but may be used for ticking messages from one room to another, and can be made the source of much instruction and pleasure.
Fig. 132.—A Simple Home-made Telegraph Key.
The key is a strip of brass fastened to a wooden base in the manner shown in Figure 132. It is fitted with a knob of some sort on the front end, so that it is conveniently gripped with the fingers.
The little bridge is made from heavy sheet-brass and prevents the lever from moving too far away from the contact on the upward stroke.
Connections are made to the key lever at the back end and the contact in front by the binding-posts, A and B. The post, C, connects with the bridge.