How to make Electronic Harmonium | 555 IC | DIY Kits | Science Projects | Kits n Spares

This harmonium can generate 15 different notes of music (one at a time). It has a PCB with 15 parallel copper strips. Each strip corresponds to one note. So as you put the probe on a strip, the instrument plays a corresponding note. IC 555 is the heart of this circuit. Here it is used as a free-running multivibrator which can produce square waves of different frequencies. Frequency change depends on the value of resistance between pin no7 and pin2 of the IC. When we put the probe on different copper strips, we are effectively changing the resistance and hence the note. The circuit can perform satisfactorily if totally ripple free power supply is provided. Hence 9v battery as a power source is recommended.

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