Simple electronic keyboard circuit

Circuit working principle: Rp1~Rp13 are the scale resistors of the electronic keyboard and
the timing resistors of the oscillator, C2 is the wide discharge capacitor, and S1-S13 are the key switches. Press any one of S1
to S13, for example, press S1, then the +6 V power supply will charge to C2 through Rp1 and S1
. Because the voltage at C2 terminal is zero at the beginning of charging, VT1 cannot be turned on. At this time, the +6 V power
supply provides base bias for VT2 through R, VT2 is turned on, and the current flows through
the speaker through the c and e poles of VT2 , and a higher voltage drop occurs at both ends of the speaker .