Chapter III

PUSH-BUTTONS AND SWITCHES

Push-buttons

Push-buttons and switches are a necessity in every home where electric bells, lights, or fans are used, for with them connections are made or broken. The telegraph-key and the commutators on a motor and dynamo are only improved forms of the push-button, and this simple little device is really an indispensable part of any electrical equipment.

The simplest form of push-button is a bent piece of tin or thin sheet-metal screwed fast to a small block of wood, as shown in Fig. 1. Under the screw-head one end of a wire is caught, and the other wire end is secured by a washer and a screw driven into the block directly under the projecting end of the strip of metal. By pressing a finger on the tin it is brought into contact with the screw-head under it, and the circuit is closed; on releasing it, the tin flies up and the circuit is opened again.

An enclosed push-button is shown in Fig. 2. It is made of the cover or body of a wooden box, a spool-end, and several other small parts. A round piece of thin wood is cut to fit inside the box and so form the base for the button. On this the spring strip is attached with screws, and the wire ends are made fast, as shown in Fig. 3. The wires are carried through the bottom of the base and along grooves to the edge, and thence to their final destination. The end of a spool is cut off and glued to the top of the box, as shown in Fig. 2, and a hole is made in the box to correspond in size with that in the spool. Through this aperture the button (cut from a wooden dowel or shaped out with a knife) passes, so that the end projects about a quarter of an inch beyond the spool. To prevent the button from falling out, a small steel nail should be driven across the inner end, or a washer may be tacked to the end of the stick, as shown in Fig. 4.

The button is mounted by screwing the base fast to the door or window casing, it being understood that the wires have been first arranged in place. The button is then set in the hole and the cap is placed over the base, covering it completely. By means of small screws, passed through the rim of the box and into the edge of the base, the cap is held in place. A coat of paint or varnish will finish the wood-work nicely, and this home-made button should then answer every requirement.

Switches and Cut-outs

In electrical equipment and experimental work, switches and cut-outs will be found necessary, particularly so for telegraph and telephone lines. Care should be taken to construct them in a strong and durable fashion, for they will probably be subjected to considerable wear and tear.

A simple switch (Fig. 5) is made from a base-block of wood three inches long, two wide, and half an inch in thickness, together with some small metal parts. It has but one contact-point, and that is the brass-headed tack (T in Fig. 5) driven through the binding-post, the latter being a small plate of brass, copper, or even tin screwed to the base-block. The end of a wire is caught under the screw-head before it is driven down. A similar binding-post is arranged at the lower side of the block, and the movable arm is attached to it with a screw. Between the arm and the post-plate there should be a small copper washer, to make it work more easily. The arm is cut from a thin piece of hard sheet brass or copper (tin or zinc will also answer very well), and at the loose end the half of a small spool is attached, with a brass screw and washer, to serve as a handle. The end of the screw that passes through a hole in the arm is riveted to the under side to hold it securely in place. This arrangement is shown in Fig. 6.

The under edges of the arm may be slightly bevelled with a file, so that it will slip up easily on the oval head of the brass tack. The drawing shows an open switch; when the circuit is closed the arm rests on the tack-head. By means of small screws this switch-board may be fastened to a table or to any part of the wood-work in a house.

In Fig. 7 a complex switch is shown. This is the principle of the shunt-box switch, of the resistance-coil, and also of the commutators of a motor. A motorman’s controller on a trolley-car is a good example of the shunt, and, with it and the resistance-coils, the car can be started, stopped, or run at any speed, according to the current that is admitted to the motor.

The complex switch is made in the same manner as described for the single switch, except that any number of binding-posts may be employed, arranged on a radial plan, so that the end of the arm will rest on any tack-head at will. Bells in various parts of the house may be rung by this switch, or it may be coupled with a series of resistance-coils to control any amount of current.

The simple cut-out (Fig. 8) is constructed in the same manner as the simple switch, except that there are two points of contact instead of one. This is the principle of the telephone and telegraph instrument wiring, so that a bell or sounder may be rung from a distance. The arm is then thrown over and the bell cut out, allowing the “phone” or key to be brought into use. In lifting the transmitter from the hook on a telephone, a cut-out is operated and the bell circuit is thrown out of action. It is in operation again directly the transmitter is returned to the hook. The switch cut-out (Fig. 9) is inactive when the arm is in the position shown in the illustration; but when it is thrown over (as shown by the dotted line) it connects the poles at opposite ends of the board. It may be thrown over in both directions, and is a useful switch for many purposes.

For strong currents the lever-switch, that rests on a brass tack-head, will not be suitable, as the switch-bar must be held firmly in place to make a perfect connection. Strong currents throw weak switches open, causing an open or broken circuit.

A single pole-switch, to carry a current up to one hundred and twenty-five volts and twenty-five amperes, is shown in Fig. 10. This consists of a base-block, a bar which is attached to the vertical ears of a binding-post, and a clutch that will hold the bar when it is pressed down between the ears.

The base-block should be made from some non-conducting material, such as soapstone, marble, or slate. If a piece of soapstone can be procured, that will be just the thing, since it is easily worked into the proper shape and size. Soapstone may be sawed and smoothed with a file; it is easily bored into with a gimlet-bit, and it is one of the best non-conducting substances. The base for this switch is six inches long, two inches wide, and as thick as the soapstone happens to be--say three-quarters of an inch. The top edge may be bevelled for the sake of appearance or left square.

Two pieces of heavy sheet copper or brass are to be cut as shown at A in Fig. 11. The ears are half an inch wide, and the total height of the strip is two inches and a half, while the part with two holes in it side by side is one inch and a quarter long, including the half-inch width of the vertical strip. With round and flat-nosed pliers bend the long ears into shape, so as to form a keeper for the bar which is then to be riveted in place. Omit the holes at the ends of the long ears in the other plate; then bend it into shape to form a clutch that will hold the bar when it is pressed down between the ears. These binding-posts should be made fast to the base-block with brass machine-screws and nuts, which will fit in countersunk holes in the bottom of the soapstone. If hard-wood is used for the base, ordinary brass wood-screws will answer very well.

The connection-bar is cut from metal the same thickness as that employed for the binding-posts and clutches; it should be shaped so as to appear as shown at B in Fig. 11. A handle should be driven on the slim end, and where the lower edge enters between the ears of the clutch, the corners of the bar should be rounded with a file. Countersunk screw-holes are bored in the base, so that it can be made fast to the wood-work.

A double pole-switch is shown in Fig. 12, and in general construction it is similar to the single pole-switch described above. The binding posts and bars are cut and bent from the patterns A and B in Fig. 11; but in this case the long, slim ends of the bars are omitted. A short turn is made at the handle end of each bar and a hard-wood block is placed between the bar-ends and held in position with screws driven through holes made in the bars and into the ends of the block. A handle is made fast to the middle of the block with a long and slim wood-screw; or a steel-wire nail may be passed through the handle and block, a burr slipped over the end opposite the head, and the small end riveted fast. When the binding-posts (to which the ends of the bars are attached) are screwed onto the base, be sure and see that the bars are parallel and the same distance apart at both ends. In like manner, when the cleat binding-posts are made fast, see that they are directly in line with the bars, so that the yoke will drop into the spaces between the ears without having to be pulled to one side or the other. This is a very useful switch for strong currents, and may be placed close to a dynamo, so that the current in both wires may be cut out at once.

Table-jack Switches

A table-jack switch is a most convenient piece of apparatus where several lines of bells, alarms, or telephone circuits are to be switched on and off.

The single table-jack switch, shown in Fig. 13, is made of a hard-wood block three-quarters of an inch thick, five inches wide, and seven inches long. It is to be smoothed and varnished, or given several coats of shellac. At the four corners small holes are made to receive slim screws, and at one end of the block five short metal plates are screwed fast, with the heads of the screws countersunk, so that they will be flush with the top of the plates. These small plates should be half an inch wide and one inch long, and may be of brass, copper, or tin. But if they are of tin the plates are made of a longer strip tacked to the board and then bent over, as shown at A in Fig. 14. They will therefore form short springs, the upper parts of which will rest against the long spring-arms. From spring brass or copper five arms are to be cut and shaped, as shown in Fig. 13. Holes are made at one end of each, and others again two inches from these, through which to pass screws.

Screw-eyes are passed through copper washers and the end holes in the strips, and then screwed into the wood plate. These will act as binding-posts, while the second line of screws will hold the plates down to the base. The arms should be bent, so that when the screws are driven down the lower edge will press on the small plates under them.

The outlet wires are attached to the binding-posts at the head of the block, and the plug (A in Fig. 13) is inserted between the arm and plate at the foot, so that contact and connection are made. This plug is a small plate of metal to which the end of a flexible wire is made fast. It should be of copper or brass, but for light work a strip of tin may be bent over with the wire caught between the plates and a copper tack passed through the sides and riveted, as shown at B in Fig. 14.

A double jack-switch (Fig. 15) is made on the same general plan as the single, but it has no binding-posts. A block of the same size is used, and two rows of short plates are made fast at each end. The arms are made with two screw-holes near the middle, as shown in Fig. 15, and through these holes screws are driven to hold the arms down to the base. Several plugs are used for each end, so that the in and out lines can be shifted, and from one to four lines used at a time.

A convenient slip-switch for single or double line work is shown in Fig. 16. This consists of a small wooden base, on which a brass arm and handle are screwed fast and connected with a binding-post (A in Fig. 16). A slip-plate is made from a piece of sheet-brass and bent so as to form a pocket into which the arm will fit. This pocket piece is connected with the binding-post B. When the switch is thrown out the circuit is broken, unless a contact-point, C, is provided, from the under side of which a wire leads out to a second circuit. When the switch is in place, as shown in Fig. 16, the circuit is closed through A and B; but when the arm is thrown out the circuit through A and B is broken and that through A and C is closed.

Binding-posts and Connectors

To make quick connections between wires and other parts of electrical apparatus, binding-posts are the most convenient device, since the turn of a screw binds or releases a wire instantly. Binding-posts may be made in many forms, but the simple ones that a boy will need can be made from screw-eyes, burrs, stove-bolts, and nuts, together with thin strips of metal and nails.

Five simple posts are shown in Fig. 17. A is made from a screw and two burrs, B from a screw-eye and two burrs, and C from a thin plate of metal and two screws, with oval or round heads. This last, however is more of a connector than a binding-post. The ends of the wires to be connected should be caught under the screw-heads or between the burrs before the screws are driven down.

In D a simple arrangement of a stove-bolt and two nuts is shown. The under bolt is screwed down tightly against the wood, and under the head a wire is made fast, so that another wire may be caught under the upper nut. If a small thumb-nut can be had in place of the plain nut, it will be easier to bind the upper wire. In Fig. 17 E a thin strip of metal may be folded over, and at the loose ends a hole should be punched through which a screw-eye will pass. The metal is held to a wood base with a screw, under the head of which a wire is caught. The second wire end is slipped between the metal plates, and a turn of the screw-eye will bind and hold it securely.

Connectors are employed to unite the ends of wires temporarily, and are made in many forms. A simple and useful one is made from a piece of spiral spring fastened to a block of wood by two staples, as shown at Fig. 18 A. The ends of the wires are pressed down into the coils of the spring and are held with sufficient security for temporary use. Another connector is made from a block of wood, a strip of thin metal, and two screw-eyes (Fig. 18 B). The metal is bent around the ends of the block, and through holes made in the ends of the strip screw-eyes are driven into the block. When the ends of wires are slipped under the metal, a turn of the eyes will hold them fast, as shown at Fig. 18 B.

A short bolt threaded at each end and provided with four nuts will also act as a connector. The inner nuts are screwed on tightly and the outer ones are loose, so that when wires are placed between them they may be tightened with the fingers, as shown at C in Fig. 18. These are a few simple forms of connectors; the ingenious boy can devise many others to suit his needs and ideas.

Lightning-arresters and Fuse-blocks

All lines of exposed wire that run from out-doors into the house should be provided at both ends with lightning-arresters, particularly if they are telephone or telegraph lines, burglar alarms, or messenger call-boxes. In many instances where unprotected telephone lines have been the plaything of lightning, painful accidents have happened, and it is only the part of prudence to provide against them. It is better to have an arrester at both ends of a line, and as the cost is insignificant it is hardly worth considering as against its feature of safety.

Lightning-arresters may be constructed in many ways and of different materials; the ones here shown and described are easily made and efficient. The principle of all arresters is simply a fuse which burns out whenever the wire is carrying a greater amount of current than is required for the proper working of the apparatus, thereby arresting the current and protecting the instruments from destruction. Induction-coils, relays, fine windings on armatures, or a magnet helix are quickly destroyed if a too powerful current is permitted to pass through them, and it is therefore advisable to protect them. When a fuse burns out under a trolley-car, or in the shunt-box of a motor-car or engine, it is because a greater amount of current is trying to pass in than the motor will safely stand. When a fuse “blows out,” the apparatus or motor is put out of commission until the fuse is replaced, but the delicate mechanism and the fine wiring on the field-magnets or armatures are saved.

The simplest form of single pole-fuse is a fine piece of lead wire held between two binding-posts, as shown at A in Fig. 19. The lead wire may be of any length; but for small instruments, where a moderate current is employed and where there is a possibility of lightning travelling on the wire, the fuse should be from two to three inches long. For inside work, however, where it is to be used simply as a safety, the wire may be shorter and finer.

To make the lightning-arrester shown in Fig. 19, cut out a hard-wood block five inches long, an inch wide, and half an inch thick. Give this several coats of shellac; then place a piece of mica, or asbestos paper, over the top of the block, and make it fast with thick shellac to act as a glue. From small pieces of copper or brass cut two plates one-half by one inch, and drill holes in them to take screws and screw-eyes. Place copper burrs under the screw-eyes for connectors, and drive two brass screws half-way down in the block through the holes at the inner ends of the binding-post plates. See that these screws fit snugly in the holes in the plates so that contact is perfect. If the holes are too large and the screws fit loosely, two copper burrs will have to be used and the screws driven in, so that the heads bind the burrs on the ends of the fuse-wire. From an electrician, or supply-house, purchase a few inches of fine lead fuse-wire--say Nos. 20, 22, or 24--and twist the ends of a length around the screws, as shown in the drawing. Perfect contact should be had between the lead wire and the screws; by way of precaution, a bit of solder will dispel all doubt. Just touch the point with a little soldering solution; then apply a soldering-iron having a drop or two of solder on the end.

Perfect connection is absolutely necessary for telephone, telegraph, or annunciator work, and where there is a lightning-arrester and the line is not working well, the trouble may often lie in the poor contact of lead and brass or copper, or possibly in using wire that is too fine. Lead is a very poor conductor, and a fine wire would act as a check. For a test, first insert a piece of copper wire to see that the line is working properly; then use lead wire of sufficient size to carry the current as well as the copper did. The action of metals and wire, as current retarders, will be explained in the chapter on resistance and resistance-coils.

For general commercial use the base-blocks of all lightning-arresters should be made of porcelain, slate, or some of the composition non-conductors, such as moulded mica, silex and shellac, or fibre. As these are not always available, wood, with a covering of mica, will answer every purpose and can be readily adapted for use.

The apparatus pictured in Fig. 19 is known as a single-pole lightning-arrester, and is the simplest form of this kind of electrical paraphernalia. In Fig. 20 a double-pole arrester is shown. This is constructed in the same manner as described for the single one. The block is five inches long, two inches wide, and half or five-eighths of an inch thick. A countersunk hole is made in the middle of all the lightning-arrester blocks through which a screw can be passed to hold the apparatus fast in any desired location.

In Fig. 21 another form of fuse is shown. It is made from a piece of mica three-quarters of an inch wide and four inches long, two pieces of thin sheet-copper, and a piece of lead fuse-wire. The copper is three-quarters of an inch wide, and one piece of it is bent in the form of a [V], as shown at A in Fig. 21. One end of the mica strip is dropped in the [V], and with a pair of pliers the [V] is closed up by pinching it at the bottom. To further insure its staying in place, the top and end, or open edges, should be soldered. Punch a small hole through the copper ends, at the inside edge, slip the ends of the fuse-wire in them, and touch the union with a drop of solder to insure perfect contact. With shears and file cut a [U] from the side of one copper band and from the end of the other; these will allow the copper ends to pass under the heads of screws, thus avoiding the necessity of removing the entire screw from the block in order to set the fuse in place.

The block on which this fuse is held is shown in Fig. 22, and is made in a similar manner to the one shown in Fig. 19, except that the metal plates are a trifle longer and are bent up, as shown in the drawing. Thus the mica fuse-plate will be elevated above the block. If the brass or copper used for the binding-post plates is too thin to stand the pressure of the screws when the fuse ends are screwed fast, put a few burrs on the screws below the plates; then the pressure of the screws cannot bend down the extending ears of the plates and make an imperfect contact.

Another form of fuse-block is shown in Fig. 23. The same sort of a fuse is employed as shown in Fig. 21, but without the [U] cuts at the ends. The clutches are made by binding brass or copper plates, as shown in the drawing; they should then be screwed fast to a base-block five inches long, one inch and a half wide, and five-eighths of an inch thick. The opening between them should just admit the copper ends of the fuse, and pressure should be used to force the fuse in place so that the contact will be perfect.

Still another form of fuse is shown in Fig. 24. This last may more properly be called a non-sparking fuse, for the lead wire is encased in a glass tube, and when it fuses no sparks fly and no small pieces of melted metal can get away from the inside of the tube. The plug is made from a piece of glass tube half an inch in diameter, two metal caps, and a short piece of lead wire. The metal caps are of thin sheet-copper, and are caught at the edges with solder. One end of the lead fuse-wire is passed through a hole in the end of a cap and soldered, as shown at A in Fig. 24. The wire is then passed through the tube and the cap placed over one end of it. This is repeated at the other end and the wire soldered fast. As a result, you will have a glass tube with metal caps held on the ends of the tube, by means of the thin lead wire which runs through the middle of the tube. The base-block to which this fuse-plug is attached is of wood one inch and a half wide, five or six inches long, and five-eighths of an inch thick. Two metal straps are made and screwed fast to the block, and the circuit wires are attached under the copper burrs and held down by the screw-eyes.

To place or replace a fuse-plug, unscrew the eyes and raise each strap slightly, so that the copper cap ends will pass under them. A turn or two of the eyes will clamp the plug in position and at the same time bind the circuit wires.

A spring lightning-arrester is shown in Fig. 25; it is simply a modified form of that shown and described in Fig. 19. The base-block is five by one-and-a-quarter by five-eighths of an inch, and is properly protected by a sheet of mica or asbestos. The two metal plates are cut for the binding-posts and screwed in place with screws, burrs, and screw-eyes. From spring-brass wire bend a hook and slip one end of it under the screw-head at the left side of the block. From a longer piece of wire make two or three turns around a piece of wood half an inch in diameter; then form a hook at one end and a turn at the other, so that it can be made fast under the screw-head of the binding-post. When at rest, the spring-hook should stand in an upright position, but when sprung and tied it occupies the position shown in the drawing. The spring-hook is to be bent down so that the two hooks are brought within an inch of each other. They are held in this position with a piece of lead fuse-wire. This last is given a turn about the hooks and one or two turns about itself, close to each hook, to prevent the spring from tearing itself away. When the wire is fused by a current the spring-hook flies up and away from possible contact with the short hook attached to the opposite binding-post. This is the construction for a single-pole-spring lightning-arrester; a double one is made in a similar manner, and the parts mounted on a wider block, as shown in Fig. 20.

For doubtful currents, where there is no means of knowing how strong they are, a combined fuse and single-pole switch is shown in Fig. 26. This is nothing more than a combination of the apparatus shown in Fig. 21, and the single-pole switch (Fig. 10). The base block is seven inches long and two inches wide. Or it may be made half an inch wider if it is to be bevelled at the top, as shown in the drawing. It should be three-quarters of an inch thick and provided with two countersunk holes for screws that will hold it in place on a ledge or against a casement. The little angles to hold the copper-ended mica fuse-plate are described for the apparatus pictured in Fig. 21. If it is desired that one of the ends should be provided with burrs and a screw-eye, the little plate of brass should be an inch long and an inch wide, with a half-inch-square piece snipped from one corner, as shown at A in Fig. 26. It is provided with two holes, and then bent on the dotted line, so that the part with the holes will lie on the block and the ear will stand in a vertical position. A reverse-plate made on this pattern will act as one side of the switch-bar clutch at the opposite end of the block. For the metal clutch and keeper at the middle of the block the metal plate (before it is bent) will appear as shown at B in Fig. 26. The long plate with two holes lies on the base, while the first ear (or the one without the hole) forms part of the clutch for the fuse end, the ear with the hole acting as one side of the bar-lever strap. An opposite plate to this forms the other side of the clutch and strap, and the two plates are screwed side by side, so that the fuse-plate will be held securely when pushed into place.

For the switch-bar use a piece of hard copper or brass four inches long, half an inch wide, and about one-eighth of an inch thick, or the same thickness as the copper straps at the ends of the mica fuse-plate. Bore a hole at one end of this bar, and with a copper rivet attach it between the two upright ears at the middle of the block. With a file cut away the two edges at the other end of the bar for a distance of an inch, so that the bar will have an end as shown at C in Fig. 26. Drive a small file-handle on this end and give it a coat or two of shellac; then bevel the lower edges of the bar with a file where it enters between the blades of the clutch. The circuit wires are made fast at both ends of the block, and the current travels through the binding-posts, the lead fuse-wire on the mica plate D, and the switch-bar. If the current is too strong, then when the switch-bar is pushed into the clutch the safety-fuse will burn out and save the apparatus; or it will arrest a flash of lightning.