This digital voltmeter is ideal to use for measuring the output voltage of your DC power supply. It includes a 3.5-digit LED display with a negative voltage indicator. It measures DC voltages from 0 to 199.9V with a resolution of 0.1V. The voltmeter is based on single ICL7107 chip and may be fitted on a small 3cm x 7cm printed circuit board. The circuit should be supplied with a 5V voltage supply and consumes only around 25mA.

Brightness of the LED display segments can be varied by adding or removing 1N4148 small signal diodes that are connected in series. Use two 1N4148 diodes for higher LED display brightness.

The use of 7805 5V voltage regulator is highly recommended to prevent the damage of ICL7107, 7660 ICs and to extend the operating voltages.

220 Ohm resistor should be connected to the PIN 4 on the first LED display.

The voltmeter can also be configured to measure different voltage ranges and display higher voltage resolution. Replacing 1M with 100K resistor will allow to measure 0 - 19.99V voltages with 0.01V (10mV) accuracy.

Use 10K potentiometer to set the reference voltage between PIN 35 and PIN 36 of the ICL7107 IC to 1V.