555 Electronic flute circuit

The circuit shown in Figure 11-16 includes the timer and voltage-controlled oscillator. IC1 (555) and R1, RP1, R2, C2 form astable multivibrator, f = 1.44 / (R1 + RP1 +2 R2) C2, the oscillation frequency and duty cycle can be changed by adjusting RP1. IC2 (CD4046) is the CMOS-type phase-locked loop (PLL), the center frequency of voltage-controlled oscillation depends on the external components, sucn as C4, RP2, RP3, R3. The center frequency fmin = 1 / (RP3 + R3) C4, fmax = 1 / (RP2 + RP3 + R3) C4. Adjusting RP2, RP3 can change the two tones of the electronic flute, adjusting RP1 can change the changing rate of two tones.