This code is to introduce the 74HC595 to drive 8 LED lights and turn them on from 0 to 8 one by one while keeping each LED on. In Project 6: Measuring DC voltage and displaying on the LED display Now, having up to 8 digits seven-segment display, it is time to measure the DC voltage of the Arduino and display it on our display. We used a variable resistor to change the voltage and see the effect immediately on the display.