Fig. 128.—An Annunciator Drop.
A drop may be made from an electromagnet and some brass strips, etc.
The frame is cut from heavy sheet-brass and shaped as shown in Figures 128 and 129.
The drop bar is a strip of metal which is pivoted on the frame at its lower end and has the upper end turned up to receive a numeral or letter.
The armature is made from a strip of sheet-iron. It is pivoted on the frame at its upper end. The strip is bent at right angles so as to fall in front of the magnet. The lower part of the armature is bent into a hook. The hook fits into a slot cut in the drop bar. A fine wire spring is placed between the frame and the upper end of the armature so as to pull the armature away from the core when the current is not passing through the magnet.
The electromagnet should be wound with No. 25 B. & S. cotton-covered magnet wire.
When a current is sent through the magnet, it will draw the armature in. This action releases the hook from the edge of the slot in the drop bar and permits the bar to drop and bring the number or letter down into view.
Fig 129.—Details of the Drop-Frame and Armature.