Samuel F.B. Morse, father of the "Morse Code" dot-and-dash communication system, also pioneered the hardware that made it work. Although other inventors had earlier demonstrated the principles of an electromagnetic telegraph, Morse, a professor at New York University, devised the first practical telegraph, including its iconic key. After Morse demonstrated his system's real-world applicability in 1841, the telegraph soon found global acceptance and grew in sophistication. Today, you can easily demonstrate the telegraph's principle with a homemade Morse key.
The Telegraph Principal
The basic transmitting side of the telegraph circuit connects a 6-volt battery, a "sounder"--a unit that uses an electromagnet to create a sound--and a Morse key--basically a switch--to transmit code over wires. At the receiving side is another sounder electromagnet. When the Morse key switch is momentarily closed, electricity flows through the circuit to the sounder electromagnets, pulling down a piece of metal and making an audible click.
Homemade Morse Key
Tack a bendable strip of tin, aluminium or copper--about ¾ inch wide by 4 inches long--to a piece of wood with a steel nail or tack. Bend the strip so it hovers over another steel nail or tack already nailed in the wood. Strip the insulation from the ends of two long wires and solder one wire to each tack (or tuck the exposed wires under the tack heads before nailing down.) You now have a simple switch. When you press the tip of the metal strip down to the tack on the board, you will be completing the circuit.
Homemade Telegraph Sounder
The telegraph sounder is an electromagnet. When electricity flows to the electromagnet, it becomes magnetised and attracts a metal strip to it, making a clicking sound. Start by hammering about a1/8-inch-diameter steel nail of into a block of wood, allowing the head to protrude by about ¾ inch. Wrap the protruding nail head with a few dozen turns of insulated wire. (When electricity flows through this wire, the nail becomes an electromagnet.) Now take another bendable strip of metal like the one you made for your telegraph key. Tack down one end of the metal and bend it so it hovers just above the electromagnet.
Completing the Circuit and Sending Code
Complete the circuit by connecting the wires that come from the two ends of your sounder to the wires that come from the two ends of your homemade Morse key. The wires now form a big loop. At a convenient place in your circuit, cut the loop and connect the ends of the wires to the positive and negative poles of a 6-volt lantern battery. Now when you press the Morse key momentarily, the electromagnet will pull the metal strip to it and make a click. That's a "dot." If you hold the key longer, the metal strip will click and stick until you release the key. That's a "dash."