Simple Digital Voltmeter Circuit Diagram using ICL7107 Circuit Diagram and Working Explanation: Working of this Digital Voltmeter Circuit is very simple. ADC inside the IC is integrating converter or Dual type Analog to digital converter. Internal ADC of this IC reads the voltage that to be measured and compare it with an internal reference voltage and converts that into the digital equivalent. Voltmeters and Ammeters | Boundless Physics A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit. An analog voltmeter moves a pointer across a scale in proportion to the circuit’s voltage; a digital voltmeter provides a numerical display.