A homemade reversing-switch, suitable for use by students of electrical and engineering courses in performing experiments, is shown in the diagram.
Referring to Fig. 1, A represents a pine board 4 in. by 4 in. and a is a circular piece of wood about 1/4 in. square, with three brass strips, b1, b2, b3, held down on it by two terminals, or binding posts, c1, c2, and a common screw, d. Post c1 is connected to d by means of an insulated wire, making them carry the same kind of current (+ in the sketch).
About the center piece H moves a disk, held down by another disk F (Fig. 2), which is fastened through the center piece to the wooden base, A, by means of two wood screws. On the disk G are two brass strips, e1 and e2, so arranged that, when handle K is turned to one side, their one end just slips under the strips b1, b2, or b2, b3, respectively, making contact with them, as shown in Fig. 2, at L, while their other ends slide in two half-circular brass plates f1, f2, held down on disk F by two other terminals, c3, c4, making contact with them as shown at y, Fig. 2.
The action of the switch is shown in Fig. 1. Connect terminal c1 to the carbon of a battery, and c2 to the zinc. Then, if you turn handle K to the right, so that the strips e1 and e2 touch b1 and b2, respectively, terminal c3 will show +, and c1 - electricity; vice versa, if you turn the handle to the left so that e1 and e2 touch b2 and b3, respectively, terminal c3 will show - , and c4 + electricity. The switch is easy to make and of very neat appearance.
How to Receive Wireless Telegraph Messages with a Telephone
Wiring Diagram for Wireless Telegraph
Any telephone having carbon in the transmitter (all ordinary telephones have carbon transmitters) can be used to receive wireless messages by simply making a few changes in the connections and providing a suitable antenna. Connect the transmitter and receiver in series with three dry cells and run one wire from the transmitter to the antenna. Connect the other transmitter wire to a water or gas pipe in order to ground it, and then hold the receiver to your ear. Any wireless telegraph message within a radius of one mile will cause the transmitter to act as a coherer, thus making the message audible in the receiver.
By using an ordinary telephone transmitter and receiver and a 1/2-in. jump spark coil, a complete wireless telegraph station may be made, which will send or receive messages for a radius of one mile. The accompanying wiring diagram shows how to make the connections. By putting in an extra switch three of the sending batteries may be switched in when receiving, thus obviating the necessity of an extra set of batteries.