10-12-2017, 02:15 PM
i want project report on electronic harmonium using ic55
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an electronic harmonium ic555
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i want project report on electronic harmonium using ic55
11-12-2017, 10:16 AM
Much is said and done about electronic music now on days when it may interest you to have practical experience in this field. To start here, it's easy to make a project. This harmonium can generate 15 different music notes (one at a time). It has a PCB with 15 parallel copper bands. Each strip corresponds to a note. Then, by placing the probe on a strip, the instrument plays a corresponding note.
The heart of the circuit is an IC with timer 555. Here the IC is used as an oscillator (or free running multivibrator, as it is technically called) that can produce square waves of different frequencies. The frequency produced depends on the note selected by the probe. A look at the circuit diagram tells us that when we place the probe in different strips, we are effectively changing the resistance between pin 7 and pin 2 (and 6) of 555. For convenience, we can denote this resistance by Rk.
Now let's look at the operation of 555 as an oscillator. If we assume that 555 has received a 9-volt power supply through pins 1 and 8, it shows the following properties:
When the voltage on pin 2 drops below 3V, the output on pin 3 changes to +9 V and pin 7 acts as an open circuit. Any change in the voltage level on pin 2 will not change the status of the IC now.
When the voltage on pin 6 exceeds 6 V, pin 3 changes to level 0V and pin 7 acts as if it had been short-circuited to ground. Any change in pin 6 will not change the status now.
In our ckt. We have connected pins 2 and 6 together. So, if we assume that the output on pin 3 is 9V, at a particular instant the combination of R1 and RK (R2 to R16) charges capacitor C3 and the voltage across the capacitor continues to increase. When it becomes just over 6V, pin 6 detects it and changes the output voltage on pin 3 to 0V and pin 7 starts to act as if it had short-circuited the ground. Then C3 starts downloading through RK. As soon as pin 2 detects that the voltage across the capacitor is less than 3V, the output is reconnected to 9V, so the cycle repeats. In this way we obtain square waves in pin 3 since capacitor c3 is charged and discharged through RK, the loading and unloading times can vary when changing the RK values and, in turn, can change the frequency of the square wave. The values of R2 to R16 (which present RK) have been calculated to give the correct ratio within 2 percent tolerance.
For a sweet musical sound, it is required to have a symmetrical square wave (which is in high and low state during equal periods of time). Therefore, R1 remains small compared to RK to achieve an almost symmetric waveform.
The types of speakers used are not critical, you can use almost any speaker. For loud sound, use at least 10 CM speakers. You can weld resistors R2 to R16 directly on the keyboard PCB.
It can be understood in the following video:
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