Your Own Milliohm Meter

We like to pretend that wires are perfect all the time. For the most part that’s acceptable, but sometimes you really do care about those tiny fractional ohm quantities. Unfortunately though, most meters won’t read very low values. There are tricks you can use to achieve that aim, such as measuring low currents through a device with a known voltage applied. It is handier though to have an instrument to make the reading directly, and [Kasyan TV] did just that with a surprisingly low part count.

The whole thing is built from an LM317, a resistor, and a voltmeter module, that’s it. [Kasyan] mentions the meter’s accuracy means the lower digits are not meaningful, but it looks to us as though there are other sources of error — for example, there’s no way to zero out the probe’s resistance except during the initial calibration. Continue reading “Your Own Milliohm Meter”

Milliohm Meter Version 1.5

A milliohm meter is a very handy piece of test equipment. Most hand-held multimeters cannot measure low resistances and bench meters that can, are usually quite expensive. [barbouri] has shared details of his milliohm meter build on his blog post, and it looks pretty nice.

When using a single pair of leads to measure very low ohms, the resistance of the measuring wires and voltage drops across the various joints become substantial enough to invalidate your measurement. The solution is to use the “Kelvin method” or 4-wire measurement. This involves passing a highly stable current derived from a temperature compensated constant-current source through the unknown resistance, and then using another pair of leads to measure the voltage drop across the resistor, which then gets displayed as a resistance on a voltmeter.

The finished project not only looks good, but is able to measure up to 2Ω with a resolution of 0.0001Ω (that’s 0.1mΩ). The project is originally designed by [Louis] from [Scullcom Hobby Electronics] and [barbouri]’s second iteration adds an improved board layout to the original project.

Continue reading “Milliohm Meter Version 1.5”