CHAPTER XV.

ELECTRIC BELLS AND BUZZERS.

APPARATUS 125.

_213. Electric Buzzer._ Fig. 100. A buzzer is, in construction, very similar to an electric bell; in fact, you will have a buzzer by removing the bell from any ordinary electric bell. They are used in places where the loud sound of a bell would be objectionable. As the buzzer is easier to make than a bell, we shall discuss it first.

214. The arrangement of the parts, (Fig. 100), is very much like that of the sounder of App. 121, Fig. 95. The armature is, in this case, a vibrating one and acts on the same principle as the automatic interrupter on App. 100, which you should study. (See Sec. 148.) The general dimensions may be taken from App. 121. The base, B, in this case is about 1 in. wide. D also is made 1 in. wide. H is 1 x 1 x 1/2 in., and is nailed to A. Through its center is a hole for the regulating screw-eye, I. The end of I presses against F. The exact position of H will have to be determined after the magnets are in place. The armature, L, should be about 1/8 or 3/16 in. above the poles. They are not allowed to strike the poles, as a screw, E, regulates that. (See Sec. 203). Y and Z are two binding-posts, like App. 46. To these are connected the battery wires. The strip of tin or copper, which forms Y, is cut like a letter T there being three holes in it, one near the end of each arm. The screw-eye, 2, and the screw, 3, are put through the horizontal part of the T, and the regulating-screw, I, passes through the hole in the vertical part which springs up against I, thus forming an electrical connection between Y and I. The magnets are made and fastened as in App. 89.

215. Connections. The inside ends of the magnet coils, (Sec. 123), are fastened between a screw-head and a copper bur, S. One outside end goes to Z, and the other under the screw, G, which holds F to D.

216. Adjustment. The part, F, and the screw, E, must be just high enough to keep L from striking the poles of M. If F is too weak, it will bend down to M. If F is too strong, it will take too much battery power to run it. In case there is not strength enough in F to quickly raise L when the current ceases to pass, arrange a screw-eye and rubber band as shown in Fig. 96. I should be slowly turned one way or the other, until it touches F just right to allow L to vibrate back and forth rapidly.

217. Operation. We shall suppose that you have all parts adjusted and the battery wires joined to Y and Z. If the current enters at Z, it will fly around through the coils, through G, F, up I, through the T-shaped tin and out at Y. The current was in L, but it could not get out at any other place than at Y. As soon as the bolts were magnetized, L was forcibly drawn down, pulling F away from I, thus opening the circuit. As the bolts were no longer magnets, F sprang right back to I, the current passed long enough to re-magnetize the bolts. This operation was rapidly repeated.

218. Use. If you wish to use the buzzer simply to call some one occasionally, a dry battery or Leclanche cell is best. This apparatus is good to work a gravity cell when it needs regulating.

APPARATUS 126.

_219. Electric Bell._ Fig. 101. Before making this bell, carefully read the directions and explanations given for the electric buzzer, App. 125. The parts are very much alike in the two instruments, and most of the lettering of them has been made the same in the illustrations. If you look at Fig. 101 from the side, with the letters M and Q at the bottom, you will see that this bell is merely a modified form of App. 125.

The Base is 7 x 5 x 1/2 in. To the upper end of this is nailed the cross piece, D. To D are fastened the binding-posts.

The Parts, F, G, H, I, J, K, L, M, N, P, Q, are the same as explained in App. 121 and 125.

The Magnet is fastened to the base by a tin strip, C, which is screwed down at both ends. By nailing a strip, like D, along the left side of the base, the magnet may be fastened to this. This strip would take the place of the base of App. 125.

The piece, F, of two thicknesses of tin, is made longer than it was in App. 125; in fact, it projects through L and forms the part N. To the lower end of N is fastened a large bullet. Hold the cutting-edge of a strong knife-blade upon the bullet, and with a few taps of a hammer drive the blade into it to make a gash.

Put the end of N into the cut, then hammer the bullet so that N will be pinched. If you have no bullet, cut a long strip of tin, about 3/8 in. wide, and wind this about the end of N to serve as a ball.

The Bell, E, may be taken from an old alarm-clock. This is not screwed directly to the base, as it would not ring well. After you have the ball, O, properly fixed, hold E, so that O will strike it near its rim; then cut a piece of wood about 5/8 x 5/8, and long enough to put under E, to raise its rim to the right place. This piece must be screwed to the base from the underside, and on to its top is placed the screw which passes through the bell. In other words, E is mounted upon a rod which is fastened to the base.

The Adjustments are made as in App. 125. By bending N a little, O can be made to tap E properly.

The Battery for a bell that is to be used much should be an open circuit one, such as the Leclanche, or the ordinary dry batteries. It is cheaper to buy a dry battery than it is to make one suitable for bells. A and B show wires that lead to the bell from the battery. One of the wires should be passed through a push-button.

APPARATUS 127.

_220. Electric Bell._ By arranging the buzzer of App. 125 with a bell, you can use the same for an electric bell. The part, F, should be made long enough to extend entirely through L, and project beyond L for about 2 in. To the end of this is fastened a large bullet, or a band of tin. (See App. 126.)

APPARATUS 128.

_221. Combination Buzzer and Telegraph Sounder._ Fig. 102. This apparatus is good for experimental purposes, where you do not wish to go to the trouble to make two separate pieces. For the dimensions and explanations see App. 121 and 125. There is but a slight change in App. 125 to make this.

222. Connections. The inside ends (Sec. 123) of the magnet wires are fastened together at S. The outside ends are joined to the two binding-posts, Y and Z, made like App. 46. A wire, P, joins Y with the screw in T, which is a piece of stiff tin or copper, which presses down upon the top of I. In this way a connection may always be had between I and T. A wire, R, joins F electrically with X; it is held under the head of the screw, G. (See App. 125 about adjustments.)

223. Operation. When you wish to use the apparatus as a buzzer, join your battery wires to X and Z. If the current enters Z, it will pass through the magnet coils out to Y, through P, T, I, F, and R to X. If you use it as a telegraph sounder, join the battery wires to Y and Z. The current will then pass simply through the coils; it will not bother to go into P, F, etc., as it has no place it can escape. If used simply for experimental purposes almost any cell of sufficient strength will do. If for telegraph, use App. 9; if for buzzer, use an open circuit cell, as, for example, a dry cell.