PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND
LIKE APPARATUS
SIMPLE SWITCHES.--We have now gone over the simpler or elementary
outlines of electrical phenomena, and we may commence to do some of the
practical work in the art. We need certain apparatus to make
connections, which will be constructed first.
A TWO-POLE SWITCH.--A simple two-pole switch for a single line is made
as follows:
A base block (A, Fig. 43) 3 inches long, 2 inches wide and 3/4 inch
thick, has on it, at one end, a binding screw (B), which holds a pair of
fingers (C) of brass or copper, these fingers being bent upwardly and so
arranged as to serve as fingers to hold a switch bar (D) between them.
This bar is also of copper or brass and is pivoted to the fingers. Near
the other end of the base is a similar binding screw (E) and fingers (F)
to receive the blade of the switch bar. The bar has a handle (G) of
wood. The wires are attached to the respective binding screws (B, E).
DOUBLE-POLE SWITCH.--A double-pole switch or a switch for a double line
is shown in Fig. 44. This is made similar in all respects to the one
shown in Fig. 43, excepting that there are two switch blades (A, A)
connected by a cross bar (B) of insulating material, and this bar
carries the handle (C).
[Illustration: _Fig. 43._ TWO-POLE SWITCH]
[Illustration: _Fig. 44._ DOUBLE-POLE SWITCH]
Other types of switch will be found very useful. In Fig. 45 is a simple
sliding switch in which the base block has, at one end, a pair of copper
plates (A, B), each held at one end to the base by a binding screw (C),
and having a bearing or contact surface (D) at its other end. At the
other end of the base is a copper plate (E) held by a binding screw (F),
to the inner end of which plate is hinged a swinging switch blade (G),
the free end of which is adapted to engage with the plates (A, B).
[Illustration: _Fig. 45._ SLIDING SWITCH]
SLIDING SWITCH.--This sliding switch form may have the contact plates
(A, B and C, Fig. 46) circularly arranged and any number may be located
on the base, so they may be engaged by a single switching lever (H). It
is the form usually adopted for rheostats.
REVERSING SWITCH.--A reversing switch is shown in Fig. 47. The base has
two plates (A, B) at one end, to which the parallel switch bars (C, D)
are hinged. The other end of the base has three contact plates (E, F, G)
to engage the swinging switch bars, these latter being at such distance
apart that they will engage with the middle and one of the outer plates.
The inlet wires, positive and negative, are attached to the plates (A,
B, respectively), and one of the outlet wires (H) is attached to the
middle contact plate (F), while the other wire is connected up with both
of the outside plates. When the switch bars (C, D) are thrown to the
left so as to be in contact with E, F, the outside plate (E) and the
middle plate (F) will be positive and negative, respectively; but when
the switch is thrown to the right, as shown in the figure, plate F
becomes positive and plate E negative, as shown.
[Illustration: _Fig. 46._ RHEOSTAT FORM OF SWITCH]
PUSH BUTTONS.--A push button is but a modified structure of a switch,
and they are serviceable because they are operating, or the circuit is
formed only while the finger is on the button.
[Illustration: _Fig. 47._ REVERSING SWITCH]
In its simplest form (Fig. 48) the push button has merely a circular
base (A) of insulating material, and near one margin, on the flat side,
is a rectangular plate (B), intended to serve as a contact plate as well
as a means for attaching one of the wires thereto. In line with this
plate is a spring finger (C), bent upwardly so that it is normally out
of contact with the plate (B), its end being held by a binding screw
(D). To effect contact, the spring end of the finger (C) is pressed
against the bar (B), as at E. This is enclosed in a suitable casing,
such as will readily suggest itself to the novice.
ELECTRIC BELL.--One of the first things the boy wants to make, and one
which is also an interesting piece of work, is an electric bell.
To make this he will be brought, experimentally, in touch with several
important features in electrical work. He must make a battery for the
production of current, a pair of electro-magnets to be acted upon by the
current, a switch to control it, and, finally, he must learn how to
connect it up so that it may be operated not only from one, but from two
or more push buttons.
[Illustration: _Fig. 48._ PUSH BUTTON]
HOW MADE.--In Fig. 49 is shown an electric bell, as usually constructed,
so modified as to show the structure at a glance, with its connections.
A is the base, B, B' the binding posts for the wires, C, C the
electro-magnets, C' the bracket for holding the magnets, D the armature,
E the thin spring which connects the armature with the post F, G the
clapper arm, H the bell, I the adjusting screw on the post J, K the wire
lead from the binding post B to the first magnet, L the wire which
connects the two magnets, M the wire which runs from the second magnet
to the post J, and N a wire leading from the armature post to the
binding post B'.
[Illustration: _Fig. 49._ ELECTRIC BELL]
The principle of the electric bell is this: In looking at Fig. 49, you
will note that the armature bar D is held against the end of the
adjusting screw by the small spring E. When a current is turned on, it
passes through the connections and conduits as follows: Wire K to the
magnets, wire M to the binding post J, and set screw I, then through the
armature to the post F, and from post F to the binding post B'.
[Illustration: _Fig. 50._ ARMATURE OF ELECTRIC BELL]
ELECTRIC BELL--HOW OPERATED.--The moment a current passes through the
magnets (C, C), the core is magnetized, and the result is that the
armature (D) is attracted to the magnets, as shown by the dotted lines
(O), when the clapper strikes the bell. But when the armature moves over
to the magnet, the connection is broken between the screw (I) and
armature (D), so that the cores of the magnets are demagnetized and lose
their pull, and the spring (E) succeeds in drawing back the armature.
This operation of vibrating the armature is repeated with great
rapidity, alternately breaking and re-establishing the circuit, by the
action of the current.
In making the bell, you must observe one thing, the binding posts (B,
B') must be insulated from each other, and the post J, or the post F,
should also be insulated from the base. For convenience we show the post
F insulated, so as to necessitate the use of wire (N) from post (F) to
binding post (B').
The foregoing assumes that you have used a cast metal base, as most
bells are now made; but if you use a wooden base, the binding posts (B,
B') and the posts (F, J) are insulated from each other, and the
construction is much simplified.
It is better, in practice, to have a small spring (P, Fig. 50) between
the armature (D) and the end of the adjusting screw (I), so as to give a
return impetus to the clapper. The object of the adjusting screw is to
push and hold the armature close up to the ends of the magnets, if it
seems necessary.
If two bells are placed on the base with the clapper mounted between
them, both bells will be struck by the swinging motion of the armature.
An easily removable cap or cover is usually placed over the coils and
armature, to keep out dust.
A very simple annunciator may be attached to the bell, as shown in the
following figures:
[Illustration: _Figs. 51-54._ ANNUNCIATOR]
ANNUNCIATORS.--Make a box of wood, with a base (A) 4" × 5" and 1/2 inch
thick. On this you can permanently mount the two side pieces (B) and two
top and bottom pieces (C), respectively, so they project outwardly
4-1/2 inches from the base. On the open front place a wood or metal
plate (D), provided with a square opening (D), as in Fig. 54, near its
lower end. This plate is held to the box by screws (E).
Within is a magnet (F), screwed into the base (A), as shown in Fig. 51;
and pivoted to the bottom of the box is a vertical armature (G), which
extends upwardly and contacts with the core of the magnet. The upper end
of the armature has a shoulder (H), which is in such position that it
serves as a rest for a V-shaped stirrup (I), which is hinged at J to the
base (C). This stirrup carries the number plate (K), and when it is
raised to its highest point it is held on the shoulder (H), unless the
electro-magnet draws the armature out of range of the stirrup. A spring
(L) bearing against the inner side of the armature keeps its upper end
normally away from the magnet core. When the magnet draws the armature
inwardly, the number plate drops and exposes the numeral through the
opening in the front of the box. In order to return the number plate to
its original position, as shown in Fig. 51, a vertical trigger (M)
passes up through the bottom, its upper end being within range of one of
the limbs of the stirrup.
This is easily made by the ingenious boy, and will be quite an
acquisition to his stock of instruments. In practice, the annunciator
may be located in any convenient place and wires run to that point.
[Illustration: _Fig. 55._ ALARM SWITCH ON WINDOW]
[Illustration: _Fig. 56._ BURGLAR ALARM ATTACHMENT TO WINDOW]
BURGLAR ALARM.--In order to make a burglar alarm connection with a bell,
push buttons or switches may be put in circuit to connect with the
windows and doors, and by means of the annunciators you may locate the
door or window which has been opened. The simplest form of switch for a
window is shown in the following figures:
The base piece (A), which may be of hard rubber or fiber, is 1/4 inch
thick and 1" × 1-1/2" in size.
[Illustration: _Fig. 57._ BURGLAR ALARM CONTACT]
At one end is a brass plate (B), with a hole for a wood screw (C), this
screw being designed to pass through the plate and also into the
window-frame, so as to serve as a means of attaching one of the wires
thereto. The inner end of the plate has a hole for a round-headed screw
(C') that also goes through the base and into the window-frame. It also
passes through the lower end of the heart-shaped metal switch-piece
(D).
The upper end of the base has a brass plate (E), also secured to the
base and window by a screw (F) at its upper end. The heart-shaped switch
is of such length and width at its upper end that when it is swung to
the right with one of the lobes projecting past the edge of the
window-frame, the other lobe will be out of contact with the plate (E).
[Illustration: _Fig. 58._ NEUTRAL POSITION OF CONTACT]
The window sash (G) has a removable pin (H), which, when the sash moves
upwardly, is in the path of the lobe of the heart-shaped switch, as
shown in Fig. 56, and in this manner the pin (H) moves the upper end of
the switch (D) inwardly, so that the other lobe contacts with the plate
(E), and establishes an electric circuit, as shown in Fig. 57. During
the daytime the pin (H) may be removed, and in order to protect the
switch the heart-shaped piece (D) is swung inwardly, as shown in Fig.
58, so that neither of the lobes is in contact with the plate (E).
WIRE CIRCUITING.--For the purpose of understanding fully the circuiting,
diagrams will be shown of the simple electric bell with two push
buttons; next in order, the circuiting with an annunciator and then the
circuiting necessary for a series of windows and doors, with annunciator
attachments.
[Illustration: _Fig. 59._ CIRCUITING FOR ELECTRIC BELL]
CIRCUITING SYSTEM WITH A BELL AND TWO PUSH BUTTONS.--Fig. 59 shows a
simple circuiting system which has two push buttons, although any number
may be used, so that the bell will ring when the circuit is closed by
either button.
THE PUSH BUTTONS AND THE ANNUNCIATOR BELLS.--Fig. 60 shows three push
buttons and an annunciator for each button. These three circuits are
indicated by A, B and C, so that when either button makes contact, a
complete circuit is formed through the corresponding annunciator.
[Illustration: _Fig. 60._ _Annunciators_]
[Illustration: _Fig. 61._ WIRING SYSTEM FOR A HOUSE]
WIRING UP A HOUSE.--The system of wiring up a house so that all doors
and windows will be connected to form a burglar alarm outfit, is shown
in Fig. 61. It will be understood that, in practice, the bell is mounted
on or at the annunciator, and that, for convenience, the annunciator
box has also a receptacle for the battery. The circuiting is shown
diagramatically, as it is called, so as fully to explain how the lines
are run. Two windows and a door are connected up with an annunciator
having three drops, or numbers 1, 2, 3. The circuit runs from one pole
of the battery to the bell and then to one post of the annunciator. From
the other post a wire runs to one terminal of the switch at the door or
window. The other switch terminal has a wire running to the other pole
of the battery.
A, B, C represent the circuit wires from the terminals of the window and
door switches, to the annunciators.
It is entirely immaterial which side of the battery is connected up with
the bell.
From the foregoing it will readily be understood how to connect up any
ordinary apparatus, remembering that in all cases the magnet must be
brought into the electric circuit.