ELECTRONIC_NOISEMAKER

Published:2009/7/13 23:25:00 Author:May | From:SeekIC

A single unijunction transistor, Q1, generates the different tones, and a general-purpose NPN transistor, Q2, raises the level to drive a small speaker. The six reed switches, S1 to S6, are mounted around the outside of the plastic pipe (Fig. B). As the pipe turns over the magnet, the reed switches open and close, tying different-valued resistors to the oscillator's frequency-control circuitry. It is also possible for two reed switches to be closed at the same time. When that happens, the output tone will be much higher in frequency than when only one switch is activated. The oscillator's frequency range can be lowered by increasing the value of C1, and raised by decreasing C1. To operate, just grab the noisemaker by the dowel rod and give it a twist to start the plastic case turning.



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