Inside a cheap set of eBay digital calipers 

another completely pointless video for ad revenue

I deal with the lack of a hold function by just pressing zero, and closing it again. Then it shows the negative of what the measurement was.

Has a screwdriver with a changable tip. Has more than one to avoid changing the tip...

I've often wondered how they made these things and managed to make them so cheaply yet with an incredible degree of accuracy. Thanks for making this interesting video.

I worked for a company for a a number of months repairing precision measuring equipment including calipers, depth gauges, height gauges, micrometers, you name it. Mostly mechanical, but also electronic versions. What you were able to surmise and figure out from what you saw, without knowing the sorts of things I was taught during training, is amazingly accurate. The main problem with those digicals is once they go wonky, there is no currently available way to repair them. With the analog ones you can always regrind, retension, rerack and realign, but the digital ones go in the recycle bin.

I looked into this technology a while back. Essentially what you have is a capacitive linear position sensor. It's not a vernier. The principal is that the teeth of the narrow comb on the sliding PCB are excited by the chip using sine waves. These teeth are in interleaved groups, and each group is fed a sine wave at a different phase. These teeth capacitively couple with the large comb on the measurement rule, which in turn capacitively couples back to the single long receiver bar back on the sliding PCB. The result is that the output from this bar is another sine wave, and critically the phase of this sine wave is determined by the position of the fine teeth relative to the large teeth. So a full 360˚ of phase corresponds with the pitch of the large teeth, 0.2 inch in this case. The chip measures this phase shift to determine the position relative to the set zero. So a 18˚ shift corresponds with 0.01 inch for example. In fact in these cheap calipers it's all done digitally. The excitation is done using PWM coded sine waves, and in the example here they're fed in differential pairs, so that's 8 signals, four pairs, 45˚ apart. The output is then very spiky, but with a sine wave envelope which is recovered by digital filtering. Somebody scoped this version a few years ago - see web.archive.org/web/20120328090506if_/www.yadro.de/pics/hp-logic-analizer.jpg. You can see the four PWM sine wave differential pairs in the 8 digital traces at the bottom, and the single output signal before filtering at the top. Just imagine the peaks of the envelope of this signal are 0.1 inches apart and the signal shifting across with the slider and you've got the idea. The reason for 56 small teeth rather than just 8 is to multiply capacitance and therefore multiply the signal output, plus averaging of any small physical inaccuracies in and impurities around the teeth. So each set of 8 small teeth in fact precisely line up with each pair of large teeth.

After 10 years mine gave up and didn't switch on anymore. I purchased another one from ebay- a metal one. What arrived was trash. Astonishingly, I was able to transfer the display, pcb and housing to the old chassis. Everything was the same. I'm astonished the parts we're interchangeable. Thanks Clive for giving me the confidence to even attempt the fix rather than send both to the bin

When these calipers came up we tested them with some small drops of water under the slider to see that they work with capacitive sensors. The instrument was in fact confused. After little drops had dried out it worked normal again.

I'm sitting here, with my jaw hanging open, laughing at how accurate these things are even after taking it apart and jamming it back together. I bought a metal one a while back, for €7 at a store called Action (in NL). It has pretty much the exact same display, buttons and battery holder cap, but in silver/grey. I'm just amazed now I learned how they work, I always thought it would be like a little scroll wheel inside, but didn't expect it to work contactless. Amazing!

When I saw Ave review one of these cheap calipers a couple of years ago, he almost made me feel ashamed of myself for owning one. You've restored my self esteem and confidence. Thanks Clive. Keep your beard in a vise.

The ending bit where you moved it as fast as possible to prove it wasn't a relative measurement has convinced me to buy one of these. The plastic, even on good models, always felt like cheap junk to me and I was sure there's no way it's actually as accurate as it wants you to believe.

It's worth keeping in mind that the flex in these calipers means that it's difficult to measure beyond .1mm without influencing the measurement just by the amount of pressure being put on the caliper.

"I wonder if this pops off". I've found that with (in)appropriate amounts of force and leverage anything will "pop off". The tricky part is getting it to pop back on again. : )

So the capacitive fingers do work exactly like a traditional vernier scale, with the wave of lined up fingers moving across then restarting at the beginning again.

Remember though, just because something displays to more decimal places, doesn't mean it's accurate...

I use digital calipers at work every day and I appreciate the amount of time I save compared to reading non electrical ones. Instant numbers showing up is such a time saver

I would imagine that, being that the wavelength of the sliding part is variable, that they are effectively self-calibrating, because moving them will emit a certain wavepattern at a certain place which the chip can then corrolate to a position along the length, even if you thrash it really fast as soon as it moves it knows exactly where it is. Also, reading if the waveform is lengthening or shortening will tell it what direction it's moving in with no other moving parts. Bloody genius.

6:18 - secret stylophone unlocked!

A buddy of mine used one of these to make an RDO for his drill press. The serial interface on these is the real secret gem. There are so many potential applications for it.

now only if there was a way to feed that data of a control board for feedback of CNC as most low end board does not have leaner encoder feedback but if it was there then all low end CNC (small PCB mill , 3D printer , Engreaver & Laser cutter )would become super accurate

As a mechanical inspector on a UK military aircraft project, who uses Vernier callipers on a regular basis (not ones supplied by Lidl may I quickly add). This strip down has been so interesting and enlightening about an item of measuring equipment I've taken for granted for so long and often wondered how they actually do work. Thank you so much.

The reason for the slight offset of the tracking pads and the "piano" board is right there in the name of the device, "vernier caliper".

Love how you checked those extra button positions for us. Again, BigClive goes above and beyond for his Patreons.

Very interesting. I use mine all the time and was always amazed at how repeatable (and probably accurate) the measurements were. Thanks for explaining how it works!

What I was told during my apprenticeship at a machining shop was that calipers are only accurate to 0.1 mm for measuring, but you can use the added digit (on professional calipers) to see about where you are with regards to the measurement. What it means is that if you had to measure something to 10.5 mm +- 0.02 mm you could not use the calipers to do that, you'd have to use the micrometers. The true accuracy and precision of a caliper should be stated in the user manual.

Thank you for this video. And it is indeed amazing to see how a cheap construction can still deliver an accurate measuring instrument.

"Carbon Fibre" or black plastic with random grit included, possibly soot (carbon) and grain dust (fibre).

The mechanical bits are important too. Straightness, parallelism, rigidity, stiffness, etc. They also have an impact depending on what is being measured. Having a locking screw and being able to use the sharp metal tips of the interior width gauge to transfer point to point measurements can be really useful. Thanks for the video!

“So i’m going to remove the battery” *firm whack* “The battery is out” This is the humor I came here for

"Lets take it to bits." Would make a great T-shirt.

"I'm going to remove the battery" *CLONK* "The battery is out."

Explanation of how it can read so precisely while using so few contacts: being advertised as a Vernier caliper, it is most likely using an electronic version of a Vernier scale. Vernier scales work by using a main scale for a larger unit, and then a smaller scale for a subdivision of that unit. the smaller scale is divided into lengths equal to the main unit minus the subdivision, so if youre between ticks on the main scale, each tick along will bring the ticks of the two scales more closely into alignment by precisely one subunit. this means you can find the scale's reading by counting along the smaller scale from the main unit you measured until you find the point at which the two scales align, and add the corresponding number of subunits. It's easy to see how the circuitry displayed would be able to achieve this, and also explains the slight mismatch in length between the groups of contacts on the circuit board and the capacitive strips on the body.

Thanks a million for this video. I'd taken mine out of a drawer for an upcoming customer visit next week, and left the calipers on my desk. My seven year old picked them up this evening, waving them around like a sword stabbing things in my office and somehow broke them into pieces. I watched your video and was able to reassemble them in a few minutes. They still work great and now my sword is fully functional again. Thank you!

This was like watching one of those nature documentaries where you see a baby bird being eyed up by lizards - you're so sure it's going to get eaten. There's no chance it could survive.... is there?

2:26 You can use the back of the head to measure distances too. Works kinda like the depth gauge, but the larger flatter surface can be useful to keep your measurement square.

Keep up the good work mate, I absolutely LOVE your witty comments and the way you look at things. Awesome !

I watched this video over a year ago but came back after measuring a soapy part of my shower. The read measurements went haywire: 0 was 0 but 20mm was 80 something and then 30 was 40 etc. it just bounced around! I thought of this video and realized the contacts must be contaminated. A quick tear-down and wipe with an alcohol pad and then re-re-watching this vid very close to understand where the pieces went - thanks Clive you saved me a few days without a micrometer and $9!!

Just got myself a cheap digital calipers today. Same type. Perfect for my level of hobby and need so far.

I bought a cheap steel digital calipers years ago after buying my first 3D printer. It's since been probably my most used tool. I love em! It's cool seeing how these take and record these measurements and it hurts my brain to think about the calculations required to interpret the signals coming from that capacitor array thing.

I've been using one of the slightly-better-but-cheap ones that go to hundredths of a millimeter. Always wondered how they work, thanks for taking the time to take those apart! I've found that hundredths of a millimeter are really useful (almost mandatory) in 3d printing since filament widths can vary by brand, anywhere from 1.6 to 1.8 mm. being able to tell 1.72 mm filament from 1.78 will often make or break a print since the volume of plastic being extruded is dependent on filament width. Also getting that first layer to come in at exactly .15 mm (or whatever you're printing at) is also really important.

I am impressed that you were able to dis- and reassemble this without once (except when quoting the eBay title) uttering the word "vernier"!

If you get a set I'd recommend storing them with the battery removed. And keep a spare battery with them. :-)

The clue is in the phrase "vernier scale" which is, according to Wikipedia, "a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation; thereby increasing resolution and reducing measurement uncertainty by using vernier acuity to reduce human estimation error": "The vernier is a subsidiary scale replacing a single measured-value pointer, and has for instance ten divisions equal in distance to nine divisions on the main scale. The interpolated reading is obtained by observing which of the vernier scale graduations is co-incident with a graduation on the main scale, which is easier to perceive than visual estimation between two points." en.wikipedia.org/wiki/Vernier_scale

"Through the magic of buying two of them . . ."

Have the same and works great. This technique could be used for digital (and motorized) potentiometers for audio mixers. The zero function can be used to set a memory location to be able to move to exactly to the same position. When motorized, it can be used to fade-in to exactly the same position. Very clever design, love it. Thank you for showing us.

We would say it is "precise" because it has more digits. Accuracy has to do with the correct number being displayed.

Just thought you would like this random bit of info, these are used to measure the thickness of the biscuits made at a factory I did a job at recently.

These cheap plastic verniers are brilliant!... I bought several of them to leave dotted in strategic places around my workplace... Plenty accurate enough for a quick measurement 👍

The clever thing of these is that they don't track the movement. They just read the position they are currently at. That enables them to still show correct values after moving the up and down at light speed haha :D Great video!

It is uncanny seeing the exact same calipers I bought a while ago being torn down by The Big Clive.

I would love to see the differences in the 0.1mm precision calipers and the 0.01mm precision version. I'm curious if it's just more lines on the respective pieces or if it's done inside the processor itself.

I was so curious all these days how these things work, thanks for explaing and showing them

There is a fourth measurement you can take with calipers like that that most people don't realize. Aside from the tail, you can also use the opposite end. Since the two parts are flush at the "Left" end, you can measure a step.

BlondiHacks says always wipe the jaws clean before zeroing out.

looks like a Vernier scale system is being used

That is actually pretty damned impressive! I figured that cheap calipers like these (I see this type often) would be absolute garbage, but it seems I was wrong, and I am very okay with that!

I bought one of these off of Amazon fairly recently and I thoroughly enjoy how great it is!

Re the very last bit: it’s actually not just tracking it at jphigh speed - the capacitive vernier system provides an absolute position, rather than relative. Or at least, it’s absolute within the repetition horizon, which is probably something like 30 cm. If they get super long, you might be able to get a situation where it’s off by , but never by a small amount.

"Let's grab a random nozzle" - that's one of my favourite party games.

Have been using these for 25 years and being an electro geek, always wondered how they worked so cheers

8:24 : The mystery button next to the inch/mm one used to allow you (in the inch mode) to switch between decimal and fractional values e.g. 1.500 → 1½ the missing button on the OFF/ON and ZERO buttons row used to be HOLD.

Incredible how it stays on track even after racking it furiously. this used to be only possible with the expensive ones. Shows that even that tech is simple and cheap to manufacture

The way I understand these encoders is this: "They work like a vernier, so...black magic and you've got a precise measure"

Excellent video Clive, very much worth the time watching.

Impossible to stop watching, super work, thank You.

I've got the exact same calipers. Had it for years, has always worked really well

Can we stop and appreciate how smoothly he popped that battery out?

This is what it's all about. Brilliant, elegant design with that element of surprise and very clever detail. Put this one on the Greatest Hits reel.

Only one thing to mention, it will not work without energy. That's why I rather like the classic industry ones. Great job thanks for the footage.

Bought one almost identical 2 years ago as to test out. It's still works and hasn't failed me.

When you peeled the sticker off the ruller part, I heard stylophones in my head

Thank glad you did the extra bit trying the buttons at the end... My head couldn't cope with the video ending and not finding that out!!!

Loved the video! Gave me the confidence to take my broken pair apart and clean the inside and bring them back to life!

Thanks to the data port (which is a premium feature in 'real' micrometers), one could build a super cheap super high accuracy linear actuator servo!

If you see and work out how a metal manual vernier works ...im sure you will see how the electronics and circuits look similar

Interference patterns are so useful. Linear scales and linear laser measurement systems use optical interference. And I've used Sony Magnascales that have two magnetic tracks along the length of the scale, 90degrees out of phase; the resulting out-of-phase magnetic fields were interpreted by simple electronics to determine position. Always a good day when you post a video. Keep up the great work, sir!

I was quite literately wondering to myself how one of these digital ones work the other day. Thanks!

I have the exact same calipers and they're totally adequate for my needs. However here's two tips; 1) Remove the battery when it's stored, otherwise it may go flat. This may be due to carrying them in my car. The jolts may be switching it on too many times. 2) If it starts to read just half of the true measurement, just remove and replace the battery. Reboot! Thanks Clive, that was very informative.

This is great, I've always wondered how these work.

I have the exact same caliper and am very impressed with it, after pressing zero and then pulling all the way back and also reading 1563mm. I use it mainly for my electric bike conversion project while also adding mudguards and other accessories that need them to accurately measure fiddly nuts and bolts washers without the guesswork and are easier to read than the manual steel version which is difficult to read after time and tarnish.

Best thorough evaluation, and especially glad you tested the mystery buttons to satisfy our curiosity. Would like to see experiments with the data connector..

Best tool ever. I have the 8"/200mm version and it measures down to 0.01mm/0.001". Sometimes I just wander round the house measuring random items because I can.

12:00 kids of certain age are screaming Stylophone !

I've used this exact mode for 3 years in the workshop. Gone through 2 batteries. still going strong (and accurately)

I love your knowledge and histories, and of course while see you tinker with electronics. I wish to have as many skill as you in this field someday. Thank you !

23:14 - Well, that's the first time I've seen anyone openly do that particular action with their tool on youtube........... :P

It's worth noting that there is a little cover that slides off to give access to the data pins without taking it apart.

Ingenious technique of sensing and measurement

Thank you for this in-depth dive. For a project I'm building, I'm wanting a DRO and digital calipers will serve the purpose well enough. I want to take it a step further, however, in attempting to relocate the 3 axes LCDs / corresponding buttons to a single 3d printed encasement higher up on the machine and, after seeing this video, I'm confident that I can easily accommodate that, even to the extent of tying all 3 on / off functions into a single on / off function that controls all 3 simultaneously. I might even be able to sort out a means to step-down volts / amps from the machine's main power to accommodate elimination of the batteries as well. I really appreciate your video.

An electronic vernier scale - pretty neat!

Fascinating, one of your very, very best!

I am at work now and watching your videos 😁 absolutely love your channel 👍

I am in Electronics hobbyst and I have been using one of these since 2008, it is doing its job just fine which is satisfactory for me.

I wanna see an Oscilloscope on it, this teardown was very interesting and I'm really intrigued now to see the waveform on those fingers to get a better understanding of how it works. Is the software comparing the phase angles and timing coming back from the fingers?

Bloody hell. I never imagined these would be so interesting to learn how they work. Amazing technology huh!

Thanks Clive! You saved me after I carelessly took apart my 12" (300mm) digital calipers and didn't note where all the pieces came from as they just fell out after I took out the screws in the wrong order. Although mine were a bit different, I was able to learn enough to reassemble (after repairing a solder joint on the + contact) and it's now working again! :-)

Thanks, Clive, I've disassembled a couple old calipers, metal and I believe one carbon fiber, as they've ended their lives, and been replaced. I came to similar conclusions without as much solid data, but appreciate your filling in the uncertain blanks. I too, find them incredibly accurate and repeatable, given their price, about 12 dollars for stainless, and five or so for the carbon fiber here in the US. Thanks again, always interesting what you find!

I calibrate these as part of my job. The spring bit that fell out we call gibs and on the steel version we have, there is 2 small screws on the top which can be adjusted to stop the jaws flexing. We call them quadri-verniers bottom points for measuring external, top points for internal, thin rod for small hole depths and the fourth measuring face is at the other end which can be used for measuring steps, so the end of the Vernier to the end that slides along the back. These should be ground square to each other. Biggest problem I find is oily residue on the face of the vernier which get in the inside of the vernier requiring stripping down and cleaning. We would never use the plastic tenth version, not accurate enough for us and even these are called verniers as the size will need very near the actual size you are measuring ;) we use micrometres, internal micrometres, depth micrometres, to ensure accuracy for small hole you get 3 legged internal micrometres accurate to about .0002" The tightest tolerance we get on things is about +/- .001" but can be just one direction. I generally calibrate to +/-.0005" for micrometres but for thread gauges it would be .0001" accuracy I'm looking for. Working in oil sector I'm stuck in Imperial sizes, but we do metric but convert sizes across from Imperial

I think one of the missing button and the missing part could be a single led and button for lighting up the screen

Brilliant - saved me taking one apart to see what was inside