Measuring SMD Parts With A Home Brew Version Of Smart Tweezers

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SMD parts are great; they allow you to pack more parts on a board, do away with drilling dozens of PCBs, and when done correctly can produce a factory-quality board made in a home lab. There’s one problem with SMD parts; troubleshooting and measuring them. The ideal solution would be something akin to the Smart Tweezers we’ve seen before, but this fabulous tool costs three hundred bones. [Kai] came up with a much cheaper solution: home brew smart tweezers that can be built for a tenth of the cost as the professional model.

What [Kai] built is an LCR meter, basically a tool that measures inductance, capacitance, and resistance in a very, very small form factor. The technique of measuring a part’s properties involves feeding a set frequency into the device and measuring the phase, voltage and current coming out. It’s all wonderfully explained by [Dave] over at EEVblog in one of his earlier videos.

The hardware [Kai] is using includes an LCD display from a Nokia phone, an MSP430-based microcontroller, a very tiny opamp near the tip of one of the points of the tweezer, and a programmable gain amplifier used to measure the components. In testing, [Kai] can measure very low-value components with a +/- 2% accuracy, and larger, more realistic components with +/- 0.25% accuracy. An awesome accomplishment, and much better than the common Chinese meters that can’t measure in the nH/pF/mΩ range.

[Kai] hasn’t gotten his pair of smart tweezers working yet – he still needs to get the circuit up and running and write some software. We’ll keep our readers apprised of [Kai]’s progress, though, and gently convince him to work with Seeed Studio or someone similar to get his version of Smart Tweezers onto maker’s workbenches the world over.

22 thoughts on “Measuring SMD Parts With A Home Brew Version Of Smart Tweezers”

    1. My meter doesn’t measure capacitance or inductance. Lacking any sort of write up, the tweezers in the ebay link appear to be no more than convenient test leads. Do you have more info?

      Kai’s probe will do inductors, capacitors, resistors, hence its “LCR” moniker.

      But I do appreciate the link to the tweezer probes. I can do with a set.

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      1. The tweezers are passive, you need to use them with your own meter (I mentioned that).

        The point of using the tweezers with a good meter is that it is likely going to be more accurate than most things one cobble up at home.

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    4. 1) The leads of the tweezer probes have their own parasitic LCR, which may be significant if you need to measure small value parts with high accuracy.

      2) My last three “inexpensive” meters with LCR measurement failed like clockwork shortly after the warranty ran out. In every case, I just turned them on one day to find them wholly or partially non-functional; even though they were working fine last time, and suffered no known damaging events. Which made them not so inexpensive. Quality alternatives with a respectable name, reliability, and warranty are *much* more expensive; but accidents can still cause you to lose your investment. So DIY test equipment, with its reasonable price, known quality, and ease of repair/modification is mighty attractive.

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      1. 1) Parasitic capacitance/inductance is a problem with any test leads, tweezers or not. That is what you have the “Zero” or “Relative mode” button on your LCR meter for.

        2) Don’t use cheap multimeters. Not worth the money. On the other hand, decent LCR meter doesn’t need to cost hundreds, there are some very good ones for around ~100bucks. E.g. this one:
        http://www.eham.net/reviews/detail/4010

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