ADC Pi Input Voltage Calculator

The ADC Pi puts a resistor voltage divider on each input, using 10 kΩ and 6.8 kΩ values to bring the incoming voltage down to a level the ADC chip can read. As supplied, that gives a maximum input of 5.06 V. You can raise it by adding a resistor in series with the input, as shown below.

This tool works out the value for that series resistor (R1) and the matching multiplier for our ADC Pi code libraries, so you can extend the board's input range to whatever maximum you need.

Enter the maximum voltage you want to measure (anywhere from 5 V to 100 V) and the calculator returns the exact R1 value and multiplier, along with the nearest E48 standard resistor value and the maximum input voltage that resistor gives you. Feed the multiplier into your code so the returned readings are scaled back to the real input voltage.