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))
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 note||Frequency [Hz]||Resistance [Ohm]|
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 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.