The scale of this circuit can produce different sounds, and different keys correspond to different scales. The electronic keyboard is played by pressing different keys with fingers to produce different scales. The principle is that the circuit NE555 is connected to an oscillator, and its oscillation frequency It is determined by the resistance of the circuit (R1-R10), so that different keys can produce different sounds. The advantages of this circuit production: simple and practical, low power consumption, and the circuit is driven by integrated circuits, with few parts, and the circuit is simple and easy to understand, which allows us to deepen our understanding of circuit principles during the debugging process. Resistors R2-R9 are the choice of oscillation frequency. They and resistor R1, C2 and NE555 constitute 9 different oscillation frequencies. The frequency selection signal is controlled by the S1-S8 key switch, and the NE555 audio output will emit a loud sound on the speaker SP. During operation, press the keys and the keyboard will emit a continuous loud sound. If you press different switches in sequence, you can try out beautiful music. colour:blue material: ABS size: 4 x 7cm Package Contents: 1 x NE555 Piano Keyboard kitOnly the above package content, other products are not included. Note: Light shooting 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.