This circuit of the scale can produce different sounds, and different keys correspond to different scales, electronic piano play is to use the fingers to press different keys, thus producing different scales The principle is that the circuit IC555 is connected to an oscillator, the frequency of its oscillation rate is determined by the circuit's resistor (R2-R9) resistance, so it be a different key to produce different sounds. Circuit principle of operation: resistors R2-R9 for the selection of the oscillation frequency, they and resistor R1, capacitor C2 and IC555 composed of eight different oscillation frequencies. The frequency selection signal is controlled by the S1-S8 switch, and the output of the IC555 audio emit a loud sound in the speaker SP. When operating, press the key, the electronic piano emit continuous loud sound, such as pressing different switches in turn, you can try to play beautiful music. LED1 is the power indication. Product Name:NE555 Electronic Piano DIY Kit Product Model:TJ-56-658 Supply Voltage:DC3-9V(DC power supply) Board Size:102x51mm Colour:As Shown Material:PCB Package Contents: 1set x electronic keyboard kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.