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  • Electronic Harmonium

  • Created: Aug 27, 2014

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Harmonium is a musical keyboard instrument that produces sound when wind sent by foot-operated bellows through a pressure-equalizing air reservoir causes metal reeds screwed over slots in metal frames to vibrate through the frames with close tolerance.

This project is a simple electronic representation of a harmonium that generate 15 different notes of music. The main component of this project is the NE555 timer IC that is used as oscillator to produce different square wave frequencies. The frequency produced depends on what note is selected/pressed.

Base on the circuit diagram, we have connected pin 2 and 6 together. So if we assume that output at pin 3 is 9V, at a particular instant the combination of 10kΩ resistor and the series of resistors charges the 0.02µF capacitor and voltage across the capacitor keeps on increasing. When it becomes slightly more than 6V, pin 6 senses it and changes output voltage at pin 3 to 0V and pin 7 starts acting as if it has shorted to the ground. So the 0.02µF capacitor starts discharging through the series of resistors. As soon as pin 2 senses that voltage across the capacitor is less than 3V, output is switched back to 9V, so the cycle repeats itself. This way we get square waves at pin 3 since the 0.02µF capacitor charges and discharges through the series of resistors. The charge and discharge times can be varied by changing values of the series resistors and in turn change the frequency of square wave.



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