Half Ohm - milliohm adapter

juuni 6th, 2012 by jaanus

Half Ohm - milliohm adapter

Half Ohm milliohm adapter is ready! Multimeter adapter that transforms any multimeter into a precision milliohm meter and debugging device. Notice that your multimeter is useless when measuring small resistances, like connectors or tracks. So did I, so I built this: 1% precise, small and cheap adapter for you. Ultra useful for finding position of shorts on your board. I have already used it tens of times. Get one!


Usage:

1. Connect the adapter to your multimeter and power both of them.
2. Half Ohm should light up brightly.
3. Switch multimeter to voltage range.
4. When nothing is connected, you can read the battery voltage. Battery is 3V CR2032, so if the voltage is lower than 2.6V, consider changing the battery.
5. When connected with a resistance smaller than 1Ω the voltage in mV shows measurement in mΩ. So 1mV = 1mΩ, 10mV = 10mΩ and so on.
6. Connect your probes to adapter and connect them both with each other (press into one pad or something like that) the readout is more or less the resistance of your probes, connections and meter itself. Zero that with RELATIVE button or just memorise it.
7. Measure the real thing, the difference between last and this measurement is your resistance.

Milliohm meter in con

Finding position of short circuits:

Connect and power everything. Press your probes to shorted tracks. Probe around. The direction where the resistance decreases is the direction of the short.

The back side

Calibration:

If you want to test or calibrate the adapter then you can use 100mΩ resistor that is included. On the bottom edge of the PCB there is big 1206 100mΩ 1% resistor that you can measure.

The sources:

Schematic and board in KiCad. My KiCad libraries! Schematic in PDF.