Simple toy keyboard circuit and principle

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

inductance

SMD aluminum electrolytic capacitor

As shown in the figure, a multi-vibrator circuit composed of a 555 time base circuit is used to change the pitch and notes by changing the on and off of the two sets of key switches. Its circuit is shown in the figure.
555 and R1-R8, R9, Cl, etc. form an astable multivibrator, change the resistance of the charging resistor (Rl-R8), can change the pronunciation frequency, and can emit different notes. The maximum resistance of the RI-R8 after series connection is 100kΩ. The basic frequency range of the illustrated parameters is 390-6420Hz, which can be changed by the K1-K7 keys (switches) of group A. During debugging, ANL and AN2 are in the off position. Use an exponential 100kΩ potentiometer to record the resistance values ​​of 1, 2, 3, ..., 7 respectively, and then select the corresponding resistance value to access the circuit. .
The B group switches A11, AN2, and R10 and R11 connected to the 555 control terminal (5 feet) are tone-tuned. When AN1 is pressed, the pronunciation pitch is higher than the basic note group (group A) by one tone; When AN2 is under, it is one level higher than the pitch of AN1. The resistance values ​​of R10 and R11 are about 500 Ω and 1000 Ω, respectively.
IC2 uses a small power integrated amplifier LM386 for dual audio signal amplification, and its volume can be adjusted by RPl. The RP1 can be used with a potentiometer for a radio with a switch (SA).