The circuit is empowered with 5 volts and it merely has two adjustments R2 of 47 K serves to put the displays on 0. To do this, we have to short-circuit the voltmeter entrance and turn slowly the R2 until we can see 0-0-0 on displays.
The variable resistor R1 serves to calibrate the power level. To regulate this, we will insert 12 exact volts at the entrance, measured with of tester or proceeding from 7812 and we continue turning R1 until we can see 12 volts.
The circuit should be empowered with a small power source, 5V, and this way the maximum measure that our voltmeter can do is 99,9 volts.
If apart your digital voltmeter you need that your power source also measures the consumed amperes, check out our assembly of a digital ammeter.
The scheme and the circuit board should be in the same folder and they should have the same name, you should only change the extension to .sch for the scheme and to .brd for the circuit board, this way both of them will be recognized and associated by Eagle.
The file to download is compressed, to extract it, you should enter a password: www.kemisa.es
If you don´t know how to make a printed circuit boards click here.