Telegraph Key and Sounder

(An Electromagnetism Project)

Introduction:

Telegraph is one of the first applications of electromagnet. In this project you will make a telegraph key and sounder.

Materials for this project (shown here) are available in all versions of MiniScience Electromagnetism Kits. 

  • Base board
  • Magnet wire
  • Key and sounder metal strips
  • Nail and screws
  • Battery Holder

Additional materials in the kit are for other projects.

History of telegraph 

The Beginning of Electronic Communications
In 1825, British inventor William Sturgeon exhibited a device that laid the foundations for large-scale electronic communications: the electromagnet. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent.

In 1830, an American, Joseph Henry, demonstrated the potential of Sturgeon's device for long distance communication by sending an electronic current over one mile of wire to activate an electromagnet which caused a bell to strike. Thus the electric telegraph was born. Samuel F.B. Morse (1791-1872) successfully exploited Henry's invention commercially.

While a professor of arts and design at New York University in 1835, Samuel Morse proved that signals could be transmitted by wire. He used pulses of current to deflect an electromagnet, which moved a marker to produce written codes on a strip of paper - the invention of Morse Code. The following year, the device was modified to emboss the paper with dots and dashes. He gave a public demonstration in 1838, but it was not until five years later that Congress (reflecting public apathy) funded $30,000 to construct an experimental telegraph line from Washington to Baltimore, a distance of 40 miles.

Procedure:
The telegraph base board in the kit comes with some pilot holes on the face of the board. Use the diagram image in the right to mark the holes with letters. This will help you in the next steps where you need to connect wires. The nail hole marked with N is a through hole that can be seen from the back of the board too.
Insert the large (3" nail) into the N hole. The nail should not exit the back of the board. Later when you install the Z shape sounder, it should be about 2mm (1/8 of an inch) above the nail.

This nail will be the core of your electromagnet.
Wrap some masking tape around the nail. Masking tape will work as an insulator and protects the wire from touching the nail. Although the magnet wire is insulated with a thin layer of resin, using masking tape is required as an additional precaution. If you don't have masking tape, you may use any other paper.
Get the spool of 28 AWG magnet wire. Leave about 12 centimeters (5 inches) from the beginning of the magnet wire and then start to wrap the wire around the nail. Wrap about 400 to 500 turns of magnet wire around the nail. Finally leave another 12 centimeters (5 inches) and cut the wire from the spool.   
You may twist the two wires near the nail to prevent the coil from being unwind. Wrap another masking tape or any other tape on the top of the coil to protect it from unwinding and accidental damage by sharp objects. Keep the two ends free and use the sand paper to scrub the insulation from about 3 cm (one inch) of the wire ends.
Insert a nail in the hole A.

Wrap and secure one wire under the A screw. Also connect the black wire of the battery holder to the same screw. The bare portion of the battery wire must be under the screw cap. Tighten the screw.
Insert a screw in hole C and connect the other end of the coil wire to the screw C.

  
Pass a screw from the hole of the small metal strip and then insert it in the hole B so that the other end of the strip is over the screw C, but not touching it.

The circuit is ready at this time. You can test it by installing the batteries and pushing the key over the screw C. The screw must become magnetized.
Install the large Z shape sounder by passing a screw through its hole and inserting it in hole Z. Position the sounder so that the long arm will stay over the nail, but not touching it. The distance between the sounder and the nail must be about 3 millimeters (1/8th of an inch).
At this time your sounder is ready for test. Push the key and the sounder's long arm must touch the nail with a click sound.
The picture on the right shows the completed telegraph key/sounder and some other materials from the electromagnetism kit.

Back to the Electromagnetism Science Kit