This device is very simple and easy to make and contains the following components:
- Arduino Nano microcontroller
- 16x2 LCD display
- LM317 voltage regulator
- and resistor 12 Ohm
It consists of constant current source of 100mAmp. Constant current source is built using LM317:
Iconst = Vref / R where: Vref of LM317 is 1.25V
Iconst = 1.25 / R
Iconst = 104mAmp
Measuring voltage drop across a resistor having constant current gives us resistance value (R = V / I), Where:
I = 100mAmp as we are using constant current source of 100mAmp
V = Measured by Arduino
This code and circuit will not work for values more than 50 Ohm as 50 * 100mA = greater than 5V.
The accuracy of this Milliometer is satisfactory and mostly depends on the accuracy of the 12 ohm resistor and the stabilized voltage of 5 volts. Finally, the device is placed in a suitable box and is another useful tool in your laboratory.