HOW TO MAKE A TELEPHONE
FOR USE AT HOME
IT is quite easy to make a telephone, which besides affording amusement,
will, at times, be found extremely useful. Fitted from the ground floor
to the rooms above, or from your friend’s house to your own, it is
impossible to overestimate its convenience.
[Illustration: FIG. 1_a_.--Section of case.]
Of course it is quite possible to buy the parts of a telephone ready
made and fitted together, but it is much more interesting to construct
the apparatus yourself.
The whole affair is so easily and cheaply made that no difficulty can
possibly be experienced, and you have only to exercise care in order to
succeed in constructing a very handy and interesting machine.
[Illustration: FIG. 1_b_.--Magnet case.]
For the apparatus to be of any practical use, a pair of receivers are
required--one for the person speaking, and the other for the person
listening.
First of all purchase two bar-magnets, _i.e._ straight and magnetized at
one end only--not the ordinary horse-shoe magnets. These bar-magnets
should be about four inches long, and can be bought from any
electrician; at the same time obtain from him an ounce of silk-covered
wire, No. 36.
Before taking the magnets from the shop it would be as well to test
them. This can be done by placing the marked end of one to the unmarked
end of the other, and unless the former is able to support the weight of
the latter, do not take either, but insist upon the electrician giving
you stronger ones.
Having made your purchase, set to work upon the actual apparatus. The
first things to be made are the wooden cases for the magnets, and these
require care in construction.
From a straight broom-handle cut off two lengths, each a little longer
than the magnets, _i.e._ about 4¹⁄₂ inches long, and split them
carefully down the middle with a chisel. Along the center of each of
these halves cut a groove (B, Fig. 1_a_), in such a manner that when the
two halves are put together they fit properly, and there is room for the
magnet to slip backwards and forwards in the hole running through them.
Now glue the parts together and you will have two short wooden tubes, or
magnet cases, as shown in Fig. 1_b_.
MAKING MOUTHPIECES
Having made the cases for the magnets, now make the mouthpieces. Procure
two wooden boxes such as boot-buttons are sold in, and glue one to the
end of each of the wooden tubes you have just made, cutting a hole in
the bottom of the box to correspond with the bore of the case. In Fig.
1_a_ you will see the work, so far as you have completed it, shown in
section. In the lid of the box cut a clean hole the size of a dime right
in the center, but this lid must not be fastened to the box just yet.
The next things to be made are two bobbins upon which to wind the
wire--one for each instrument. Cut a piece of fairly strong cardboard
about ¹⁄₄-inch wide and just large enough in circumference to fit the
marked end of the magnets tightly. Divide your No. 36 wire into two
equal lengths, and wind each piece around the bobbins, leaving the two
ends free to the length of about two inches.
Next slip the magnet, M, into the groove, and push it through so that
the bobbin, L, is contained in the box C, Fig. 2. Make two holes in the
bottom of this box, pass the ends of the wires through them and fasten
them with binding screws, as in the illustration H, Fig. 2.
The thin plate which vibrates with the voice must next be made. Obtain a
smooth piece of very thin sheet-iron--of just such a texture as is used
by photographers for ferrotypes. Take the greatest care to keep this
perfectly flat. Cut two round pieces large enough to cover the
mouthpieces as you will see in P, Fig. 3, where it is shown in section.
Take the lid in which you have already cut the circular hole and fasten
it to the box in such a way that it keeps the iron plate in position (Q,
Fig. 3).
[Illustration: FIG. 2.--Arrangement of magnet.]
[Illustration: FIG. 3.--Section of completed instrument.]
[Illustration: FIG. 4.--Connection with battery.]
Push the magnet very close to, but not quite touching, the disc of
iron--say ¹⁄₁₆th of an inch away, and fasten it in that position, either
by means of a wooden plug at the other end, or by driving a screw into
the case in such a way that it grips the magnet and holds it firm (S,
Fig. 3). Fill up the hole at the other end of the case with a piece of
cork, glue or screw on the lid, keeping the opening so that it almost
touches the iron disc, and your telephone is complete. Fig. 3 shows in
section how it should now appear.
It remains only to make the connections with the batteries in the manner
shown in Fig. 4, and you will be able to speak with your telephone. It
is very possible, however, that the voice will carry faintly, but do not
be disappointed, as this can be very easily remedied by making an
apparatus which is usually attached to the telephone, and is known as
THE MICROPHONE
[Illustration: FIG. 5.--Sectional view of microphone.]
This instrument, as its name implies, serves to make small sounds
greater. Besides being useful in conjunction with a telephone, it is
also of interest in itself.
Make a base, BC, and an upright, A, from a piece of thin pine wood, as
shown in Fig. 5. Buy from the electrician two blocks of carbon such as
are used in batteries (these will cost but a few cents), each measuring
about a cubic inch. In one side of each of these blocks fasten a long
binding screw, whilst in an adjacent side make a hollow with a
rat-tailed file or a penknife. Then get a small pencil of charcoal such
as is used in the large arc lamp, and cut off a piece 4 inches long;
file both ends to a point in the way that you sharpen a pencil (E, Fig.
5).
Having made these various parts, fit them together. Screw the two pieces
of carbon to the upright in such a way that one rests upon the base
whilst the other is at such a height that the charcoal pencil rests
lightly in the hollows, between the two carbons, as in DD, Fig. 5.
The microphone is now complete, and can be attached to the telephone as
shown in Fig. 6. It will be found to increase the sound to such an
extent that your voice will be distinctly audible, and conversation
perfectly clear.
[Illustration: FIG. 6.--Connection of microphone and telephone.]
By attaching one receiver and the battery to the microphone as shown in
Fig. 7, very slight sounds will be increased to an extraordinary degree.
The ticking of a watch seems like so many heavy footfalls, and if you
can succeed in getting a fly to walk across the sounding-board, as the
base is called, the footsteps will be plainly heard. Many interesting
experiments can be performed in this manner, and as the microphone is so
easily made, it is well worth constructing one for the sake of such
experiments alone.
[Illustration: FIG. 7.--Experiment with microphone.]