This is a low cost milliohm meter which can be put together by using 2X INA219 current sensor, Arduino nano, 2X16 LCD display, 150 Ohms load resistor and simple arduino code which the library can be found online. The beauty of this project is no precision current reference is needed as the current sensor will take care of the measurement.
Step 1: Put the Current Sensor Together
Since INA219 current sensor uses I2C as it communication protocol. Put them together in parallel connection and assign each board with its unique address will do.
Step 2: Solder the Sensor Board Together With Arduino Nano
Solder both the INA219 current sensor board together with Arduino nano in accordance to the schematic show above. The top current sensor 100mOhm resistor was removed.
Step 3: Continue Adding in the LCD and Load Resistor to the Board.
Connect the LCD and load resistance to complete the system. The 150 Ohms load resistance is used to limit the current passing through the DUT. It was used to limit the current to below 100mA with the input voltage of 12VDC.
Step 4: Complete System
The completed system as shown. Basically one of the current sensor board will be used to measure the current in the close loop system. As we know current in a close loop without any brunches is the same. The second INA219 board is used to measure the voltage drop across DUT. A simple Ohms Law can be used to calculate the resistance on the DUT. V = I * R; R = V / I in Ohms.
Step 5: Arduino Sketch