Digital circuit production 09-NE555 eight-tone electronic keyboard

1. Circuit simulation and principle explanation

      Eight buttons control the resistance value connected to pins 2 and 6 of the 555 chip. When S8 is closed in the picture, the resistance value connected to the circuit is 10K. Together with R10 and C4, it constitutes the charge and discharge parameters of the 555 multivibrator circuit. , at this time, pin 3 outputs a frequency, check it with an oscilloscope; when only S1 is closed in the circuit, the resistance value connected to the circuit is 2K+2K+2K+2K+2K+2K+1K+10K, and the The frequency is approximately equal to the frequency of the musical scale Do; if S1 and S2 are closed at the same time, due to circuit characteristics, only S2 will work. Based on this, a smart person can design a circuit that can produce a polyphonic effect by pressing two buttons at the same time.

2. Precautions

(1) There is no distinction between positive and negative poles when welding the speaker, just connect one to the output and the other to ground;

(2) The frequency calculated by the resistance parameter is close to the actual tone, and some deviation from the actual tone is normal;

(3) If there is no sound after pressing the button, check whether the chip is inserted backwards and whether the solder joints are weakly soldered.