If you are able to secure the electromagnets from a discarded electric bell they will work fine for the magnets M1 and M2.  They should be disconnected from their iron support and mounted upon some non-magnetic material, such as brass or copper, making the distance between their centers as small as possible.  The piece of metal upon which the magnets are mounted should now be fastened, by means of two wood screws, to the back of the board, shown in Fig. 6, that is to form the face of the annunciator.  It should be about 1/8 in. thick, 1/2 in. wide and long enough to extend a short distance beyond the cores of the magnets M1 and M2.  Drill a 1/16-in. hole through its center, as shown in Fig. 2.  Drive a piece of steel rod into this hole, making sure the rod will not turn easily in the opening, and allow about 1/2 in. of the rod to project on one side, and 1-1/2 in. on the other side.

Drill a hole in the board upon which the magnets are mounted so that when the long end of the rod carrying the armature is passed through the hole, the armature will be a little more than 1/16 in. from each magnet core.  The short end of the rod should be supported by means of a piece of strip brass bent into the form shown in Fig. 3.

Drill a hole in the center of this piece, so the rod will pass through it.  When the armature has been put in its proper place, fasten this strip to the board with two small wood screws.  You may experience some difficulty in locating the hole in the board for the rod, and it no doubt would be best to drill this hole first and fasten the magnets in place afterwards.

Two small collars should be fastened to the rod to prevent its moving endwise.  Fit the collars tightly on the rod to hold them in place.

Cut the long end of the rod off so it projects through the face of the annunciator about 5/8 in.  Take some very thin sheet brass and cut out a needle or indicator as shown in Fig. 4.  In a small piece of brass drill a hole so it will fit tight on the other end of the rod.  Solder the indicator to this piece and force it in place on the end of the rod.

When the armature is the same

[Illustration:  Details of the Annunciator]

distance from each core, the indicator should be parallel to the long dimension of the face of the case.  The case of the instrument may be made in the following way: 

Secure a piece of 3/8-in. oak, or other hard wood, 3 in. wide and 2 ft. long.  Then cut from this board the following pieces:  two whose dimensions correspond to those of Fig. 5 and are to form the sides of the case; two whose dimensions correspond to those of Fig. 6 and are to form the back and the face of the case; three whose dimensions correspond to those of Figs. 7, 8, and 9 and are to form the lower and upper end of the case and the finish for the top.