Arduino Voltmeter with LCD

Overview

A resistor divider scales the voltage below 5 V, then the board converts the reading back and prints it in volts.

Build Steps

1. 1

   Build the divider

   100 kΩ in series with 10 kΩ from the test point to ground; take A0 from the junction.

2. 2

   Read and scale

   Convert A0 to volts, multiply by 11 (the divider ratio plus the meter's own offset) and average several samples.

3. 3

   Show the result

   Print the voltage on the I2C LCD with two decimal places.

4. 4

   Stay safe

   Never measure anything above 30 V, and do not measure mains; discharge capacitors before probing.