Digital voltmeters can measure a range of alternating current (AC) voltages, direct current (DC) voltages, or both AC and DC voltages. Devices typically display between three and seven digits. Some digital voltmeters can capture minimum and maximum voltages called spike readings.
In the picture below is a series of simple digital voltmeter using the Seven-segment display, this series based ICL7107.The ICL7107 is a 3 1 / 2 digit LED A / D convertor. It contains an internal voltage reference, high isolation Switches analog, sequential control logic, and the display drivers. The auto-zero adjust ensures zero reading for 0 volts input.