Simple Music Maker

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The basic idea was to create simple electronic music instrument which based on analog electronic. Below is schematic of this device:
schematic

It is an astable multivibrator based on 1/2 of LM358 op amp. Second part of LM358 was used to create virtual ground. Here is equation for output frequency of op amp:

f=1/(2 * R5 * C1 * ln (1+B/1-B))
where
B=(R3/(R4+R3))
When we choose value of R3 equal to 0.9 of R4 then equation for output frequency have following form:
f=1/(2 * R5 * C1)

 

Here are list of music notes and corresponding values of resistors:

Music noteFrequency [Hz]Resistance [Ohm]
C55239560
D55878517
E56597587
F56987163
G57846377
A58805681
B59885060

 

Device is powered by single 3V battery and could be connected by mini-jack cable to portable speaker. Buttons are placed in roller made from paper. PCB could be placed inside this roller.

Here is example photo of PCB:
pcb

Here is video of first run:

 

 

As further steps in improvements it is possible to create polyphonic musical instrument by using for each music note separate op amp.