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. 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 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., Weight: 0.13448197982 pounds, Manufacturer: Jaywool