555 DC voltage measuring instrument circuit diagram

As shown in the figure, the control terminal pin 5 and the threshold terminal pin 6 of the 555 are actually the two input terminals of the internal voltage comparator I. As long as the voltage of pin 6 is higher than pin 5 by 5mV, the 555 will trigger reliably.

Apply DC voltage to the + and - terminals in the figure. If the voltage is high, LED1 will light up; if the voltage is low, LED2 will light up. Change the measuring range and RP1. When the two LEDs flash alternately, multiply the measuring range by the RP1 indication, which is the measured voltage in volts. The measurement range has four levels: 0-1V, 0-10V, 0-100V, 0-1000V.