6 ms·
Making Electronic Calipers
- satiric 2y agoI don't actually see an accuracy number, only the claim of "millimeter precision", which is actually pretty bad for calipers. Looks like a fun project though. Basically a linear resolver sensor I guess. From how much effort the author has put into the project I'd estimate the accuracy is much better than +/- 0.5mm.
- Arcanum-XIII 2y agoWhich is quite low. My manual caliper is precise to the 1/10 of a mm, my electronic to 1/100 (but I would say 0,02 is the more realistic) The manual one is not good, harbor freight quality, electronic is a mituyo (not an entry level). Still - good ROI on both, got the electronic one because my eyesight is not that good anymore.
- jcgrillo 2y agoWith a decent set of vernier calipers (I have Brown and Sharpe ones) they're accurate to 0.001" (0.02mm) every time. But what's nice about analog measuring tools is you can actually reliably achieve better accuracy--like 0.0005" +/- 0.00025"--by "reading between the lines". I can reliably take finishing cuts accurately to a few ten thousandths of an inch using vernier calipers (confirmed by checking with a micrometer accurate to 0.0001"). The only application I've encountered where digital tools work better for me is having a DRO on a mill is extremely convenient.
- varjag 2y agoYou really want to use a mike on this kind of precision. Calipers can be repeatable in a certain range but even then a readout from vernier gives too much error. Measuring a tenth of mm is acceptable (tho I'd never trust a vernier caliper measurement beyond 0.2). A hundredth IMO is wishful thinking.
- jcgrillo 2y agoLooking at my calipers now I noticed that the imperial side is twice as precise as the metric side. Graduations of 0.05mm vs 0.001". I wonder why that is.
- genewitch 2y agotenths and hundredths of an inch "don't mean anything" because we don't divide inches that way in common use, but in subtractive manufacturing and the like they do use "thou" - and 0.001" is a thou. Personally, i use microns instead of 0.001mm, too, when measuring that small. I forget the accuracy of my good calipers, but i could detect errors of around 2 microns if memory serves. It's been a long time since i cared about anything that accurate so i have two pairs of cheap plastic ones - scale and digital.
- jcgrillo 2y agoYeah I only use calipers and micrometers for machining--I haven found any use for additive manufacturing--and never in metric units because all my tools are imperial. Just strange the calipers punish metric users by giving them only half the precision.
- Moru 2y agoIf you buy a tool in a country that is mainly using imperial, the markings on it might be more exact for the imperial measurement. Might be the opposite in a country with metric. Just guessing though but that is often how other things work out.
- Symbiote 2y agoA Google image search for "caliper" shows several have 0.001in and 0.02mm accuracy, which is similar. For 0.01mm there are only electronic or dial calipers.
- varjag 2y agoA typical metric micrometer is accurate to 0.01mm (tho you can find more precise ones at premium). It's really unlikely you'll get a micron precision from any calipers. Even an angry glance warms up the instrument enough to make this meaningless. Microns are the domain of grinding and lapping, you rarely ever need to go there with cutting.
- nuancebydefault 2y agoI really cannot understand that you talk about micro meter (um) accuracy on a caliper. If you apply a tiny bit more pressure or it is under a tiny angle, the error is at least tens of um.
- rowanG077 2y agoIt depends what you are measuring. Some plastic piece? Of course this has a ton of flex. A solid steel shaft? No way you can flex it tens of um.
- nuancebydefault 2y agoYou don't need to flex the material you are measuring to get tens of microns difference. Simply both sides of the caliper will not stay parallel since there is always some dust or fluid between the sliding pieces. The dust will simply flex.
- rowanG077 2y agoOf course. To get a good reading you have to clean both surfaces. I mean if you want to wring blocks together it won't work without clean surfaces either.
- jcgrillo 2y agoTry it! You might surprise yourself. EDIT: ah, I see your confusion. A "micrometer" is an aliased term. It means both "a millionth of a meter" and "a tool for measuring very precisely". I used the latter meaning above. Although in terms of order of magnitude precision they're identical--a micrometer accurate to 0.0001" is accurate to 2.54e-6m. It's possible to get within a handful of µm with decent calipers. Easier with a micrometer.
- eth0up 2y agoThe proper term for calipers, for me, is Mitutoyo. I really want one of the solar models.
- HeyLaughingBoy 2y agoInteresting that you say that. My current backburner project is a display (TFT or PC) for Mitutoyo Digimatic. I can read the bright VFD display, but it struck me that others might find it difficult to read from across a workbench.
- penneyd 2y agoArticle states +/- 0.6mm
- deskr 2y ago> Have you ever wished for a 500 Hz, millimeter-precise linear position sensing system Kind of, but I'd like an 0.01mm precision please. It can be just a few Hz, I don't need 500 Hz. Great project though!
- tonyarkles 2y agoI'd be super curious to see how the accuracy changes with averaging out/low-pass filtering the measurements. Accuracy usually improves proportional to sqrt(N) when you take N samples so your higher precision desire might just be a bit of code to write. The other side of it though is that you're starting to get down into the "everything needs to be temperature controlled" region as you squeeze that precision number. FR-4 and copper have thermal expansion coefficients around 15-20ppm/C. If I'm doing this mental math correctly, a 5 deg temperature rise would make a 1m long piece of FR4 expand by 0.1mm, or a 10cm piece of FR4 expand by 0.01mm.
- foobarian 2y agoOne time I wanted to demonstrate thermal expansion to my kid (1st grade or so) so I made some marks with a steel ruler and put it in the freezer. Imagine my surprise when we took it out and there was no perceptible difference :-D
- dekhn 2y agodid you measure the freezer after? It expanded :)
- satiric 2y agoWith some microcontrollers you can do this "averaging out" just by changing ADC parameters, you don't even have to write the low-pass-filter code.
- auxym 2y agoThat is specifically sigma-delta type ADCs: https://www.analog.com/en/resources/technical-articles/sigmadelta-adcs-tutorial.html https://www.analog.com/en/resources/technical-articles/sigma...
- contingencies 2y agoTLDR: <0.02mm should be possible w/open source using cheap fabs. Interesting project. The hardware guy earlier built a rotary encoder and a vape pen. I am no metrologist (though by chance I once worked for the UK guy who brought Hexagon to China and made bank), this looks overall like quite a complex scheme that was probably referenced from an existing implementation. These days you can get 0.10mm pitch tracks and offsets ("4 mil") or 0.09mm ("3.5 mil") from JLC on 2 layer/4+ layer. With flex PCBs you can get still smaller pitch ("3 mil"). Combining a few rows of these with basic multi-track rotary encoder theory should give you portions thereof, ~0.01-0.02mm. This back of hand calculation aligns well with my Mitutoyo's test report, which states maximum permissible error is 0.04mm @ 5mm diameter, 0.02mm @ 0-200mm, and 0.03mm @ 300mm. Indicated errors on the test report are all in the range of 0mm-0.02mm except inside radius which is 0.03mm. This would be a standard high grade caliper level of precision. In practice, achieving these levels is going to require machining high grade steels and mounting them at high levels of parallelism, not simply working out the electronics. See also: https://www.eevblog.com/forum/projects/absolute-capacitive-rotary-encoder-(acre)-constructed-out-of-two-pcbs/ https://www.eevblog.com/forum/projects/absolute-capacitive-r... (see animation, GC7626C datasheet) https://github.com/littleboot/ACRE https://github.com/littleboot/ACRE
- echoangle 2y ago> TLDR: <0.02mm should be possible w/open source using cheap fabs. What does that have to do with a Fab? Isn’t a fab the thing that creates ICs? PCBs aren’t made in a fab.
- contingencies 2y agoFab is simply short for fabricate or fabrication which is a term commonly used in all manner of manufacturing including circuitboards. An external party that provides manufacturing is often referred to as a 'fabrication partner' or 'fabricator', shortened to 'fab'. https://en.wiktionary.org/wiki/fab#Noun https://en.wiktionary.org/wiki/fab#Noun https://en.wiktionary.org/wiki/fab_lab#English https://en.wiktionary.org/wiki/fab_lab#English https://en.wiktionary.org/wiki/fabricator#English https://en.wiktionary.org/wiki/fabricator#English and if you really want to understand the English culture don't miss https://en.wikipedia.org/wiki/Absolutely_Fabulous https://en.wikipedia.org/wiki/Absolutely_Fabulous ;)
- echoangle 2y agoInteresting, I always naively assumed that those cheap calipers measure distance mechanically, with something like a wheel and an encoder. The actual method is much cleverer. Also, nitpick: „ I’m stuck in the local optima of …“ should be „optimum“.
- userbinator 2y agoBe sure to watch Big Clive's video that's linked in the article. It's amazing how cheap digital calipers have gotten, and how accurate they are at that price. They probably use a 4-bit MCU or an ASIC to do the calculations and output the data --- both to the screen, and an often-hidden serial port. The use of a non-absolute encoding leading to drift, and the higher standby power consumption which was distinctive of the infamous battery-eating Mitutoyo clones, seems to have been largely solved within the past few years. There are even solar models available for not much more.
- XorNot 2y agoI would love some solar powered calipers. "I'll wing it" measurements for me are usually powered by "god damn it, do I even have any more CR2032's? Is the battery cover pressing down enough? Screw it where's a ruler..."
- userbinator 2y agoSolar calipers are around US$10 at the usual far-East online shops.
- moreati 2y agoRecommend you take the CR2032 out when not using the calipers. Cheap/no name ones (atleast those sold 5-10 years ago) have a relatively high standby current, even when the LCD screen is off.
- janci 2y agoI just flip the coin cell around so it stays in the device but does not deplete (reverse polarity but in fact the contacts will not touch the battery poles so no harm).
- DoctorOetker 2y agoWould you happen to know the current draws for the older and newer designs? I would like to check if mine are worth replacing (since I dutifully remove and store the battery in the designated holder in the case I can't rely on durability comparisons because it would depend on usage patterns).
- _ea1k 2y agoFrom reading the headline, I thought this'd be about brakes and was really confused.
- bigiain 2y agoI wonder if this technique could be used in typical stepper motor controlled "step counting" 3d printers and CNC mills, to provide closed loop servo-like control? Have real time micrometer-precision measurements of your x, y, and z axis - and feed that back unto your control loops?
- Marthinwurer 2y agoThis is basically how Digital ReadOuts (DROs) work on manual milling machines, and I'd assume they use the same thing on CNC machines as well.
- mikewarot 2y agoLong ago, as a member of Pumping Station One in Chicago, I had a fellow member cut out a series of 0.1" fingers spaced on 0.2" centers, and stuck them on a long piece of aluminum stock, and was able to use a Harbor Freight caliper to read the aluminum as a scale without further modification. It really doesn't take much more than an accurate set of interdigital electrodes to make a working scale.
- deleted 2y ago[deleted]
- lynaghk 2y agoAuthor here. Lots of questions about precision --- in the article I calculated 0.6mm as the standard deviation of 200ms worth of phase measurements (n=124) while the slide wasn't moving. I'd love to hear any advice/ideas re: - approaches for figuring out what's currently limiting the accuracy (i.e., noise sources) - the relative merits of averaging in time vs phase domain - how to improve the analog frontend (See my collaborator Mitko's github repo for the hardware schematics: https://github.com/MitkoDyakov/Calipatron/blob/main/Hardware/V1.1/Schematics%20V1.1.pdf https://github.com/MitkoDyakov/Calipatron/blob/main/Hardware...)
- jcgrillo 2y agoSuper cool project! I don't have any answers but really appreciate learning how these things work.
- jcgrillo 2y agoToo late to edit, and somewhat off topic, but I wonder if you could package an interferometer in such a way to work for calipers? https://caltechexperimentalgravity.github.io/IFO.html https://caltechexperimentalgravity.github.io/IFO.html
- jcgrillo 2y agoAgain, too late to edit, but there's some interesting related content here: https://hackaday.io/project/5283-potpourri/log/21475-laser-internferometry-discussion https://hackaday.io/project/5283-potpourri/log/21475-laser-i... https://hackaday.com/2015/07/24/self-built-interferometer-measures-nanometer-displacement/ https://hackaday.com/2015/07/24/self-built-interferometer-me...
- YZF 2y agoI kind of glossed over your article but one thing that stood out is that you preferred to lower the adc sample rate. That doesn't make sense. Usually the way you want to set something like this up is with a low pass filter before you sample it and you want to sample at a high enough rate (some multiple of that filter frequency). This is due to the sampling theorem. Maybe I'm missing something. I would aim for the highest possible sample rate and then post-process the signal (assuming that's computationally reasonable, i.e. you can keep up with real time). There are general practices/principles for minimizing noise. Having a ground plane. Separating your digital electronics from your analog electronics. Clean power supply. Shielding. Another thing I'd be concerned about is that this whole thing is a big antenna. Yet another concern is that motion might influence the results (any time you have conductors moving in the presence of fields you get some induced current). Commercial positioning solutions are usually based on optics and gratings. I wonder if that's a better approach even for a hobbyist. Something like an optical mouse just linearized...
- jccalhoun 2y agoMy dad was a machinist so he always had calipers. I never thought I needed a set until I bought a cheap pair for under $10. I use it all the time. The only problem? I'm left handed so I either end up using it upside down or trying it with my left hand and then switching to my right. They make left handed calipers but the cheapest I've found are over $40. I think I'll keep fumbling with the cheap ones.
- mft_ 2y agoSame (except the left-handed challenges) - I have a pair that were probably <€10 on AliExpress, are good enough, and get used all the time.
- kevin_thibedeau 2y ago> Rust’s formal compile-time machinery doesn’t support trigonometry C++20 can do this in a consteval. It is a godsend for embedded table generation.