William Slyke.

In a house where there are several entrances and rooms, and electric connections are desired to ring a call bell, an instrument called an annunciator or indicator is used. Bells of different tone are sometimes used, but when the number of bells is more than three or four, it is very hard to distinguish between them. An indicator, which shows from what room or place the call comes, is desirable. Indicator movements take a variety of forms, but may be divided into two distinct forms, viz.: Those which drop a shutter or move a disc, in which the shutter or disc requires to be reset each time a signal is sent in; and those which require no resetting, depending for their action on a swing or pendulum movement, which, when started, continues for some time. The latter kind are called pendulum indicators, and is the kind to be here described.

Of the two kinds, the pendulum indicator is much to be preferred, as an extensive use of the former has proved that persons cannot be relied upon to replace the shutter, so that when the bell rings there are two or more shutters down, thus causing more or less delay in answering the call. As there are a number of magnets used in the construction of an indicator, the builder is advised to buy the magnets, as they will be cheaper to buy than to make; but if one wishes to make them, a full description will be found in the November, 1901, number of Amateur Work.

A magnet is needed for each call, to be connected to the indicator, and another for a relay. (See Fig. 1.) Two magnets are fastened to a soft iron base, L, Fig. 1. One or two magnets may be used, but two are better. A piece of soft iron about 1/8" in thickness by 1/2" wide, and just long enough to reach from one end of one core to the end of the other core of the magnets (M, Fig. 1) forms the armature. To the top of the armature solder a very thin piece of steel or other springy metal, about 11/4" long and 1/8" wide (N, Fig. 1). A binding-post, J, with a hole and set screw, is inserted into base B of the indicator.

The end of the steel spring is made small enough to fit tightly in the hole of the binding-post. To the other end of the armature is soldered a piece of stiff wire about 11/4" long. To the end of this wire is soldered a piece of tin or other light metal, about 1" long and 3/4" in width; this is the vane upon which the name or number is placed. In many of the commercial forms a piece of silvered glass (looking-glass) is fastened to the wire instead of metal, as this can be readily seen in a dim light.

Fig. 1.

Push the end of the spring in the binding-post until it just reaches the other side of the hole, and fasten it down with the screw. The binding-post is put in a position so that the armature hangs as shown in Fig. 1. The armature should hang 3/8" from the top of the cores of the magnets. Now test the vane by fastening it in a vertical position so the vane hangs down. Connect one wire of the magnet to the pole of a battery; the other end of the wire is just touched to the other pole of the battery. As soon as the second wire comes in contact with the battery the armature will, if the vane is all right, be attracted to the magnet G G and held there until the circuit is broken. As soon as this occurs the vane and armature is released and will swing to and fro for some time, finally stopping in its normal position. Make as many of these vanes as there are rooms or other places to be connected with the indicator; three are shown in Fig. 2.

Fig. 2.

As an electric bell is used with the indicator to tell when a signal is sent in, a relay is frequently employed in conjunction with the pendulum indicator, as the continual make and break of the circuit by the bell sometimes interferes with their satisfactory working. As its name implies, it relays another battery into the circuit. A relay is used in telegraphy and many other forms of electrical apparatus. It is made as follows: A magnet is fastened to a soft iron base just like the vane. The armature is made also in the same manner as the armature' of the vane. It should be pivoted at the top, as shown at J, Fig. 3, but may be fixed the same way as the armature of the vane. To the other end of the armature is soldered a strip of metal 11/4" long and 1/4" wide, and should be as thin as a medium-sized clock spring. Two binding-posts with small holes and set screw are inserted in the base, as shown at B and C in Fig. 3. To the post B is fastened a piece of wire 10" or 12" long, No. 20 gauge, to be used for connections. A piece of a wire nail 1/4" in length is inserted in the hole of each binding-post, the top screw is then screwed down to firmly hold the nail. It is very important that there should be only a very small space between the armature and the cores of the magnet, and the metal strip should rest lightly against the post C but not quite touch the post B when the relay is at rest. If a speck of platinum can be soldered to the nail in post B, and another speck on the metal strip just where the strip touches the nail, a better contact is made, but if all the parts are kept clean it is not abso lutely necessary.

A piece of planed board is now procured, large enough to hold all the vanes and the relay. Three binding-posts are needed for the relay, and one for every vane put on the board, as shown in Fig. 2. The inside connections are as follows: Fasten all the vanes to the board, and place the relay in the right-hand side as in Fig. 2. From post B of the relay a piece of annunciator wire is brought to binding-post 6, Fig. 2. A piece of wire is soldered to the armature of the relay and carried to post 5. The end of the lower magnet wire of the relay is connected with the bottom wire of each vane magnet. (See Fig. 2.) The upper wire of magnet on the relay is carried to post 4, and the upper magnet wire of each vane is carried to a separate binding-post. The outside connections can be readily seen by examining Fig. 4. Post 6 is connected to post on bell. A piece of wire is carried from zinc of battery to the other post of the bell. A wire is carried from post 5 of indicator to carbon of battery Z. The connections of battery X are: Carry a piece of wire from zinc of battery to post 4; from carbon of battery carry a length of wire to each pushbutton in the different rooms, and from push 1 a piece of wire to post 1 on indicator, etc.

Fig. 4.

A top can be put over the vanes and relay with holes through which to see the numbers of the rooms. If a single-stroke bell is used, a relay is not necessary, and the bell is connected just like the relay, cutting out the wires of binding-posts 5 and 6. The working of the indicator is as follows : A person in room 1 pushes the button in that room, this closes the circuit of vane 1 and the relay. The magnet attracts the armature and holds it until the push is released, when the armature is released also and begins swinging. The armature of the relay is also attracted, and in coming to the magnet it brings the metal strip in contact with the nail in post B; this closes the circuit of the bell, which rings until the push is released.

Fig. 3.