This milliohm meter is a home made version of a usually highly priced tool made using a circuit based on an Arduino Nano. It is able to measure resistances in the range of 0.1mOhm to 1299.99 ohm with 3 scales. The design and build process is fully explained in an instructables article.
Could result very useful for measuring small resistors, resistance of PCB traces, motor - inductance - transformer coils, or calculate the length of wires.
The device uses a kelvin connection that prevents the leads to create measurement errors.
The 5V rail of the circuit comes from the 5V regulator of the Arduino Nano, this causes a severe overhead inside the case as the main voltage is 12V, I fixed it adding an LM7805 bolted to the case.
Other issue is that the error about ~1% is not noticeable withing the first 100 units of each scale but, for the bigger figures it is a problem, for solving this I did a calibration KIT and a procedure for calibrating the device by software.
This two problems have leaded to the second version of the meter that has calibration by hardware, IoT conncetivity, an ePaper display and more, but is not finished/published yet.
Video showing how to calibrate the device.