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Electro-buzzer
Nail board B and
wooden blocks C and D onto board A (about 5 x 5 inches). Push an iron bolt F
through a hole
bored in B. Wind covered copper wire G 100 times round the bolt and connects
the ends to a battery and to H respectively. Bore a hole through block C and
wedge the fret saw blade H firmly into it so that its end is a short distance
from bolt F. Hammer a long nail K through A and bend it so that its point rests
in the middle of the saw blade. Oil the point of the nail. Use a piece of beading
E as a key, with a rubber band P as spring and drawing pins M and N as
contacts. Join all the parts with connecting wire (remove the insulation). If
you press the key down, you connect the electric circuit, bolt F becomes
magnetic and attracts H. At this moment the circuit is broken at K and the bolt
loses its magnetism. H jumps back and reconnects the current. This process is
repeated so quickly that the saw blade vibrates and produces a loud buzz. If
you wish to do Morse signaling with two pieces of apparatus, you must use three
leads as in the lower
circuit diagram.
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