Using an integrated circuit CA3162 and some electronic components can be made a simple handheld voltmeter . In this digital voltmeter, the voltage measured is digitized in an analog-digital converter (A / D) and then displayed with three decimal. The display type is not usually seven segments, but consists of three groups of ten LEDs.
Range is up to 1V (at full scale), can be extended up to 10V or more, using the voltage divider R1-R2-R3.
Measured value is read on three LED bars: the first one, D1 - D10, indicate units: the second, D11-D20, decimals: and the third, D21 - D30, hundreds. The circuit is zeroed with P1, in this case the entry left in the air diodes D1, D11 and D21 are on (diodes D10, D20 and D30 is figure 9).
Then, apply a known input voltage and adjust P2 until LEDs indicate the correct value.