Arduino Milliohm Meter

This is an accurate milliohm meter with a maximum resolution of 0.1mOhm. The design is very simple, the whole assembly can be built in a couple of hours once all the parts are gathered. It is based on a precision current sink and a high-resolution ADC controlled by an Arduino Nano V3. It uses a Kelvin connection with the resistor under test to exclude the resistance of test leads from the measurements.

Arduino Milliohm Meter

It can be very useful for measuring small resistors and the resistance of PCB traces, motor coils, inductance coils, transformer coils, or calculate the length of wires.

Measurement ranges:

  • Scale 0m1: 0.1mOhm to 12.9999 Ohm.
  • Scale 1m0: 1mOhm to 129.999 Ohm.
  • Scale 10m: 10mOhm to 1299.99 Ohm.

Step 1: Parts and Wiring Diagram

  • The file WiringAndParts.pdf attached to this step shows all the parts of the milliohm meter with the buying link, and how to connect them.
  • The main circuit (1) contains the Arduino Nano and the rest of the electronics. This circuit has been designed by me and can’t be purchased, but it is fully described in following steps.
  • The power comes from a wall adapter (D) that is connected directly to the 2.1mm power jack female socket (2).
  • The 2×16 display (3) shows the current scale set and the value of the resistor under test. It is connected using the I2C bus.
  • The binding posts/banana jacks (4) connect the circuit to the test clips (B).
  • There are two pushbuttons (5). The black one is connected to the “SEL” connector. When this button is pressed the scale change. The red one is connected to “CAL”. When this button is pressed the meter enters in HOLD MODE.
  • All the parts are contained in an orange Hammond 1590B aluminum box (A).
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