We found this circuit that makes use of CMOS technology in a 1988 publication. The circuit has independent oscillators for each note, as well as adjustment or tuning. Capacitors from C2 to C13 determine the frequency of each note; The circuit also includes automatic switching of the supply voltage and a built-in low-power amplifier. The TIP31 of this amplifier must be equipped with a heat sink. The keys are of the conductive sponge type, touching the conductive plate sectors for each note.
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