How Two Boys Made Their Own Electrical Apparatus Part 13

If just to show the principle of it, almost any cell of medium strength will do, like that of App. 3, 4 or 5. A dry battery will do, but if you use the sounder much, an open-circuit battery will soon use itself up.

Where much work is needed of the battery use App. 9.

[Ill.u.s.tration: Fig. 95.]

The Key like App. 119 is best. Push-b.u.t.tons are handy where used only for experiments, and not for the actual sending of messages.

APPARATUS 121.

_199. Telegraph Sounder._ Fig. 95. This makes a simple and efficient sounder for short lines. The base, B, is 7 4-1/2 7/8 in. The back, A, is 7 4-1/2 1/2 in.; it is nailed to B. The piece D is 4 3/4 3/4 in.; it is nailed to A. C is a wooden piece 1-1/2 3/4 3/4 in.; it is nailed to A, and in its top is a screw, E, which is used as a regulating-screw to keep the armature, L, from touching the poles.

200. The Armature, L, is explained as App. 77. The two thicknesses of tin at F must not be too thick, or it will take too much battery power to work the sounder. If you find that it is too stiff to bend down, when the current is on, try the arrangement of App. 122, which is easier to make and regulate. The whole point depends upon the tin you have. The end of L must tap against E. A hole is punched in the part F, and a screw, G, holds it to D. L should rest about 1/8 in. above the poles and gently press against a screw or nail, V.

201. The Magnets are like App. 89. They are made as in App. 88, and held down like App. 90. These should be placed very near the back, A, so that the armature will be over them. If your yoke is not too wide the coils may rest against A. Y and Z are binding-posts like App. 46.

202. Connections. Join the coils as explained in -- 125 and see -- 115.

Instead of a third or middle binding-post, as in Fig. 66, hold the two inside ends between a screw-head and a copper bur. The method of joining the wires for a line with two outfits, is shown in App. 124. If you have but one key, sounder, and battery, simply join the line wire to the return wire there shown. A gravity cell is best. (See App. 9.)

203. Hints About Adjusting. If you have the right spring to the part F, of the armature, you will have no trouble. It must not be so weak that it allows L to strike upon the poles, as the residual magnetism (Text-book) will hold L down after the current has ceased to pa.s.s. No springs are necessary, if your tin is right. Do not have L too far away from the poles. The distance is regulated by the position of V. If you have trouble in getting it to work see App. 122. The poles must be opposite in nature.

APPARATUS 122.

[Ill.u.s.tration: Fig. 96.]

_204. Telegraph Sounder._ Fig. 96. The magnets, connections, etc., are like those of App. 121, no binding-posts, etc., being here shown. The armature is straight, however, the part F resting upon D. A hole is made in the end of F, and through this is a screw or nail, S. The hole must be large enough to allow S to pa.s.s through easily. This acts as a bearing or pivot. L is kept up against V by the rubber-band, J, one end of which pa.s.ses around the end of L; to the other end of J is a thread, which is tied around a screw-eye, K. By turning the screw-eye, the band may be made to pull more or less upon L. In this way the apparatus may be regulated according to your battery. The general dimensions and explanations are given in App. 121. D is made of such a height that it will bring L about 1/8 or 3/16 in. above the poles.

APPARATUS 123.

[Ill.u.s.tration: Fig. 97.]

_205. Telegraph Sounder._ Figs. 97 and 98. This apparatus looks a little more like a regular sounder than App. 121 and 122, but it is much harder to make and adjust. In this the lower nuts of the bolts are not sunk into the base, and the magnets are made of 2-in. bolts. If you change this and fasten them like App. 89 and 90, it will simply change the dimensions of the small parts. The sizes given are for this particular instrument.

Fig. 97 shows a perspective view, and Fig. 98 is a plan or top-view of it, with dimensions.

[Ill.u.s.tration: Fig. 98.]

206. The Base, B, is 6 4 7/8 in. The magnet, M, is explained in App.

89. Its wires are attached to the binding-posts like App. 46. The armature, A, is 2-1/2 3/4 1/8 in., and made as described in App. 71.

The piece, D, is 2-1/2 1-3/8 1/2 in., and is screwed to B from below, after the two uprights, C, are nailed to it. The uprights, C, are 2-3/4 7/8 1/2 in. They are nailed to D. The nail, N, runs through both uprights, and acts as the bearing for F to rock up and down upon.

The hole for N is 2 in. above B. It must not be too loose in the holes, or F will rock sidewise, and allow A to touch one of the magnets. The upright, E, is 2-3/4 3/4 3/4 in., and is screwed or nailed to B from below. A screw, G, is put into the side of E near the top. This screw has the underside of the head filed flat, and against this the screw, L, taps when the armature is attracted. The arm, F, which carries the armature, A, is 4-1/2 1/2 1/2 in., and is pivoted by means of N, which pa.s.ses through it and the uprights C. F must swing up and down freely. The hole for N, in this model, is 1-3/4 in. from the armature end.

207. The armature is fastened to F by a screw, S. A copper bur is put under the head of S to aid in keeping A from rocking sidewise. Through F, and about half way between C and L, is put a screw, I, the lower end of which taps against the head of a screw, H, which is put into D. By uns.c.r.e.w.i.n.g H a little, F will be raised, and A will be brought nearer the poles of M. The rubber-band, J, is placed over the head of I, and has tied to it a thread, O, which in turn is tied to a screw-eye, K. K screws into the end of B, and by turning it one way or the other, the tension, or pull, on J may be increased or diminished. There must be enough spring in J to pull A up after the current ceases; it must not pull so much that the magnet cannot draw A down hard enough to make a good click between L and G.

The Magnet, M, is explained in App. 89, and the construction of one bolt magnet is given in detail in App. 88. In this particular sounder the bolts are 2 in. long under the heads, thus bringing the tops of the bolt-heads about 2-1/4 in. above B. M is held to the base by a band of tin, T. The yoke may be screwed to B, as suggested in App. 90. This is the better plan.

208. Adjustment. You will find, although you make all of the parts with the dimensions given, that you will have to try, and change, and adjust before everything will work perfectly. A must not be allowed to touch the poles of M when it is pulled down, on account of the residual magnetism, which would keep it pulled down. Adjust this with F. The armature must not be pulled too far up from the poles of M by the tension in J; adjust this with I and H. If your battery is weak, the pull of J must be small, just enough to raise A.

The Battery. It is supposed, if you make an instrument like this, that you expect to use it for a line. In that case make a regular gravity battery like the cell of App. 9. See Fig. 99 for line connections, and Fig. 98 for plan view of this sounder.

APPARATUS 124.

_209. Telegraph Line; Connections._ Fig. 99 shows the complete connections for our telegraph line, with two complete outfits. The capital letters are used on the right side, R, and small letters are on the left side, L. The batteries, B, b, are like App. 9. The keys, K, k, are like App. 119. The sounders, S, s, are like App. 121 or 122.

[Ill.u.s.tration: Fig. 99.]

210. The two stations, R and L, may be near each other, or in different houses. The return wire, R W, pa.s.ses from the copper of b to the zinc of B. This is important. If the cells are not joined properly, they will not work. It is better to have the cells together, on a short line, joined in series. The line wire, L W, and the return wire, R W, may be made of insulated copper wire for short lines in the house. Ordinary annunciator wire, No. 20, is good and cheap. The kind that is double cotton wrapped, waxed, and paraffined, has about 235 ft. to the pound.

You should get at least 5 ft. for 1 cent. If your line stretches from one house to another you will find it better to use iron wire.

Galvanized iron or steel wire No. 14 is good. This size weighs about 100 lbs. to the mile. The return and line wires must not touch each other at any point; they must not touch any pipe or other piece of metal that will short circuit your batteries. It is best to use porcelain or gla.s.s insulators to support your wires if the line is long; but for short lines, where you use a return wire, you may support the wires upon poles or trees by means of loops made of strong cord or wire.

211. Operation. Suppose R (right) and L (left) have a line. By studying Fig. 99 you will see that R's switch, E, is open while e is closed. The whole system, then, has but one place where the circuit is open. As soon as R presses his key, K, the circuit is closed, the current from both cells rushes around through K, S, L W, s, k, b, R W, and B. This magnetizes the bolts of both S and s, and their armatures come down with a click upon the regulating-screws, where they remain as long as the current pa.s.ses. As soon as R raises his key the armatures rise, making the up-click. R can, in this way, regulate the time between the two clicks. If he presses K down and lets it up quickly, the two clicks that his friend L hears from s are close together; this makes what is called a dot. If R holds K down longer, it makes a longer time between the clicks for L to hear, and this makes a dash. R, of course, hears his own sounder, which is making the dots and dashes also.

As soon as R has finished, he closes his switch, E. L then opens his switch and proceeds to answer. Both E and e should be left closed when you are through talking.

(Read -- 194, 195, and study what is said in App. 9 about the gravity cell to be used on such a line.)

_212. Telegraph Alphabet._ The letters are represented by combinations of dots, dashes and s.p.a.ces. A dot is made by pressing the key down, and raising it at once; that is, the key is raised as soon as it strikes.

This makes the letter E. The dash is made by pressing down the key, and allowing the current to pa.s.s about as long as it takes to make 3 dots; this makes the letter T. A long dash for L should take about as long as for 5 dots. s.p.a.ces occur in a letter and between words. To make a dash you hesitate while the lever of the key is down, to make a s.p.a.ce, you hesitate while the key is up. H is made with 4 dots without hesitation or s.p.a.ce. By putting a s.p.a.ce between the dots the letter &, Y or Z is made according to the position of the s.p.a.ce. Notice that letters containing dashes do not contain s.p.a.ces. A s.p.a.ce is really the opposite of a dash. The letters C, E, H, I, O, P, R, S, Y, Z, and & are made entirely of dots or of dots and s.p.a.ces.

You should notice that several letters are the reverse of others; A is the reverse of N, B of V, D of U, C of R, Q of X, and Z of &. The student should study some book upon telegraphy, if he desires to become expert. Punctuation marks are left out of the alphabet here given, as boys will find very little use for them.

A _ ___ B ___ _ _ _ C _ _ _ D ___ _ _ E _ F _ ___ _ G ___ ___ _ H _ _ _ _ I _ _ J ___ _ ___ _ K ___ _ ___ L ______ M ___ ___ N ___ _ O _ _ P _ _ _ _ _ Q _ _ ___ _ R _ _ _ S _ _ _ T ___ U _ _ ___ V _ _ _ ___ W _ ___ ___ X _ ___ _ _ Y _ _ _ _ Z _ _ _ _ & _ _ _ _

1 _ ___ ___ _ 2 _ _ ___ _ _ 3 _ _ _ ___ _ 4 _ _ _ _ ___ 5 ___ ___ ___ 6 _ _ _ _ _ _ 7 ___ ___ _ _ 8 ___ _ _ _ _ 9 ___ _ _ ___ 0 ______

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 -- 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 1 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 -- 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, pa.s.ses 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, (-- 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.

[Ill.u.s.tration: Fig. 100.]

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 pa.s.s, 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.