It’s remarkable how tiny electronics have become. Heaven knows what an old-timer whose experience started with tubes must think, to go from solder tags to SMD in a lifetime is some journey. Even the generation that started with discrete transistors has lived through an incredible shift. But it’s true, SMD components are tiny, and that presents a challenge aside from the one you’ll face when soldering them. Identifying and measuring the value of a chip component too small to have any writing upon it becomes almost impossible with a pair of standard test probes.
Happily the test equipment manufacturers have risen to the challenge, and produced all sorts of meters designed for SMD work that have a pair of tweezers instead of test prods. When I was looking for one I did my usual thing when it comes to Hackaday reviews. I looked at the budget end of the market, and bought an inexpensive Chinese model for about £16($21). And since I was browsing tweezers I couldn’t resist adding another purchase to my order. I found a pair of tweezer test probes for my multimeter which cost me just over a pound ($1.30) and would provide a useful comparison. For working with SMD components in situ, do you even need the special meter?
A Packet Full Of Tweezers Arrives
So in due course my package from Shenzhen arrived, what had I bought? The tweezer test prods were of anonymous origin, but the meter came in a blister pack with a manufacturer’s name and model number. This was it seemed a Chinese-language package, but a bit of Google Translate work revealed it to be a Shenzhen Binjiang BM8910 (translated). Opening the package revealed a CR2032 battery for it, plus a Chinese warranty card and a folded set of English instructions. Installing the battery produced an instant power-on, with the meter entering a scanning mode trying to identify what was across its terminals.
You can tell a lot about the quality of an imported product like this one by the quality of its instructions. Those for the BM8910 are a pleasant surprise, with mostly decent English and well-presented diagrams. The unit itself is about the size of a chunky marker pen, yellow plastic with an LCD display, a couple of buttons, and the Chinese for “Chip resistor/diode/capacitor intelligent tester” according to Google Translate on top. It parts in the middle, and one end slides off to reveal the tweezers themselves, which are insulated spring steel with pointed probes attached to their ends. The instruction leaflet claims that these are gold-plated, I have to say it doesn’t look very golden to me. Aside from this, the overall quality and feel of its construction is good, this may not have cost much but it does not feel too cheap.
Turning it on by pressing the “func” button, and it enters an automatic mode in which it tries to identify the component in the tweezer as a resistor, capacitor, or diode, and give a reading. Pressing “func” repeatedly steps it through individual autoranging resistance, continuity, diode tester, and capacitance modes, and holding the button down turns it off. The other button is a “hold” button, convenient for retaining a reading.
So having investigated the BM8910, I set to with a variety of SMD boards and modules around my bench. Gripping a part was easy enough, though 0201s require a little care as you might expect. and in most cases the instrument correctly identified their function and value. It becomes a quick way of determining manufacturing quality, for you soon see what tolerance components have been used by the variance in their values. It is worth noting that the continuity function does not have the buzzer you might expect.
As a general point, most component measurements seemed unaffected by their placement in-circuit. An LED series resistor on an Arduino, for example read exactly as it should have. But in cases where RC networks affect the perceived value across a component as you might expect the readings it returns can not be trusted as the value of that component. In general it seems to prefer identifying the resistance of whatever circuit it sees, and if that includes an inductor it defaults to the DC resistance of that component.
I’d say that if you’re in the market for a not-too-expensive SMD tweezer tester, SZBJ BM8910 is a good option. But this review isn’t over, because I also bought those SMD tweezer test probes for my multimeter. If you’re a really frugal engineer, how do they rack up against a dedicated instrument?
But How About The Basic Option?
For not a lot of money it’s fair not to expect much in the way of quality. These these £1 wonders are functional tweezers with a plastic grip and a single flex about 50cm (1’6″) long that splits into two wires with 4mm plugs for the meter terminals. The tips of the tweezers aren’t as nice as those on the BM8910, being just the plated spring steel of the tweezers themselves. Operation is simple: plug it into the meter, and you’re good to go.
Gripping SMD devices is easy enough, and identifying resistor values is yet again fairly straightforward. The same issues with networks of components apply, and of course you are limited in what you can measure by what your meter is capable of. Mine doesn’t have a capacitance range, so I was only able to compare the two on resistance and diode testing, on which it compared favourably. It was however extremely useful to be able to measure voltages in-circuit with a device powered on, and I suspect that this is what these probes will end up being used for.
The inexpensive SMD tweezer probes are not the highest quality tool you’ll have on your bench, but they are so cheap that it’s an easy choice to add to your arsenal. They aren’t really as convenient as the dedicated instrument for measuring the values of SMD components, but they do bring all the meter’s capabilities to bear and it’s extremely convenient to be able to measure voltages. Buy a set, you’ll find them useful.
This review started as a comparison between two ways of measuring SMD devices on PCBs, and ended with a recommendation to buy both the decent option and the cheap one if you have that requirement.
Regular readers will have followed the occasional series of reviews here of inexpensive imported tools and test equipment, and will know that sometimes the cheapest in the catalogue can be entertainingly bad. In this case it’s a pleasant surprise that the ultra-cheap probes were useful, but perhaps the key to a successful cheap tool lies in extreme simplicity.