8 ms·
How cheap digital verniers work (2017)
- deleted 4y ago[deleted]
- criddell 4y agoWhy do so many cheap digital calipers have an issue with the zero point jumping to 0.2" or 5.08 mm?
- jstanley 4y agoI've never observed this behaviour, but presumably it's because 5.08mm is about the width of one of the pads on the "T"-shaped section, and it falsely detected a movement when there was none?
- ly3xqhl8g9 4y agoIt's much weirder than that: you can close and open the vernier in a particular fashion (very slow and then very fast, it's an art) and keep adding 5.08mm in quantum steps: 5.08, 10.16, 15.24. The largest value I got on a boring day was around 200mm, on a 150mm vernier.
- londons_explore 4y agoI'm kinda surprised it doesn't self-reset when closed and then opened fully. That would be a very easy way to automatically 'fix' any location ambiguity with software-only changes.
- ly3xqhl8g9 4y agoYes, as noted, it probably is some shared firmware bug, it's just too consistent across vendors.
- mschuster91 4y agoIt would need some form of precise detection for that event, which would be expensive.
- deleted 4y ago[deleted]
- ly3xqhl8g9 4y agoIt's such a constant bug across cheap vendors that there are only two possibilities: (i) a global conspiracy from Big Vernier, (ii) all the vendors in cause are using the same buggy firmware.
- dTal 4y agoIt's right in the article: >The comb on the vernier shaft has a tooth pitch of 5mm. In other words, if the slider instantly moved 5mm, it would be undetectable, or 'ambiguous'.
- pie314isi 4y agoIf they don’t have a vernier scale they’re just calipers
- DanTheManPR 4y agoThis must be a regionalism; I've never heard of them called "verniers" before.
- causality0 4y agoThank you. That was driving me nuts.
- fortran77 4y agoNo, that's what a socket set is used for.
- geocrasher 4y agoReminds me of the time I went into a pub right on the docks of a fishing port. An old seafarer came in and sat next to me. When I asked him about the ships steering wheel shoved down the front of his pants he just looked at me and said "Yar, it's drivin' me nuts!"
- jameshart 4y agoI mean, from reading this the way they work is by detecting the relative offset of two slightly differently pitched scales by measuring a series of capacitances. Honestly it’s a much more ‘vernier’-like mechanism than I’d given it credit for.
- cmiller1 4y agoI've run into several older engineers that call all calipers "verniers." It used to bug me but I guess it's okay for language to be a bit flexible like that. I still call the shelf in front of me in my car the "dashboard" even though it's not blocking the rocks kicked up by a dashing horse anymore.
- jstanley 4y agoI had always assumed that they worked like optical mice (i.e. shine a light at a slightly-textured surface and watch the surface move underneath), but it's much simpler than that.
- londons_explore 4y agoOptical mice actually aren't good at precise relative positioning because the way the lens is setup, if they are moved slightly closer to the surface they 'see' more movement. You would imagine that you could use some kind of registration pattern(s) to solve this, but sadly nearly all mouse sensors are made by Avago, and Avago runs their own algorithm on the raw sensor data, and won't let you have the full data stream (you can only receive it via a debug API which only lets you get the data out super slowly). The avago ROM's are built into the sensor, and run a little 8080 CPU with a neat DSP for processing the image data, but sadly the system has too little RAM for any exploit to run your own code on it.
- bloopernova 4y agoOh lord that would be an amazing hack in a story. A super secure facility gets compromised despite using custom firmwares on everything, but the mouse sensor slipped through the cracks.
- Cthulhu_ 4y agoI think you wouldn't get very good sub-millimeter precision with optical; I'm not very well versed in the subject, but infrared has a wavelength of between 780 nm and 1 mm, these things have to be more accurate than that.
- amluto 4y agoThe little PCB pads are something like 500000nm across, so 780nm is nothing. You don’t need a sharp picture of the thing you’re looking at to locate it.
- pjc50 4y agoYou can get very high precision with light using a similar technique: cause interference patterns. This lets you do sub-wavelength measurement. See also https://en.wikipedia.org/wiki/Very-long-baseline_interferometry https://en.wikipedia.org/wiki/Very-long-baseline_interferome..., where the wavelengths are typically larger than light.
- schneems 4y agoWhat do the expensive ones like mitutoyo do differently? I’ve got a pair and the are definetly more consistent than $30 neikos.
- jstanley 4y agoI assume the same, but possibly implemented more precisely.
- shimonabi 4y agoIf you leave the battery inside a cheap caliper, the battery will be dead in a couple of hours, even if the caliper is switched "OFF".
- dsfyu404ed 4y agoThis is obvious BS. Many of them get packaged and shipped with the battery in them. That said, they absolutely do eat batteries faster than the expensive calipers.
- shimonabi 4y agoIt's not. I take the battery out after each use. Several users have reported this, for example: "Turns out they pull almost as much current off (15uA) as they do on (17uA)." https://www.reddit.com/r/harborfreight/comments/z7j8hp/fixed_my_caliper_battery_drain_issue_for_good/ https://www.reddit.com/r/harborfreight/comments/z7j8hp/fixed...
- rsaxvc 4y agoAn LR44 supplying 15 microamps will last more than 9 months before depleted. This base level of current draw obviously matters to different users differently.
- aidenn0 4y agoPossibly not if you buy the LR44 from Amazon. I have gotten batteries labeled "LR44" that were practically useless. I've also gotten "SR44"s that were actually LR44s.
- michaelt 4y agoArticle author here - apologies if you can't see the charts, it seems in the time since 2017 some subresource-integrity-related issue has arisen. I'll try to look into that, but in the meantime I can assure you that you're not missing too much :)
- toss1 4y agoLoved the "Hello NoScript Users! A graph will appear here if you enable javascript for ...". Accurate. Very cool bit of work and writeup, I use these all the time but never did a teardown — thanks!
- adolph 4y agoBig Clive also covered this a couple years later. Has more of an emphasis on the teardown and schematic. The comments are also great for links to other people's findings. This article is great for more details about how the electrons move. https://www.youtube.com/watch?v=fKSSY1gzCEs https://www.youtube.com/watch?v=fKSSY1gzCEs I'd like to adapt the concept using flexible pcbs to make a largish Nest-style rotary encoder. To understand Vernier measurement conceptually, the Wikipedia article is actually not bad: https://en.wikipedia.org/wiki/Vernier_scale https://en.wikipedia.org/wiki/Vernier_scale
- Animats 4y agoThe key insight is in the patent: "The transmitting electrodes are powered with A.C. voltage in such a way that an electrical rotary field forms which generates A.C. voltages on the receiving electrodes, and the phase position from the transmitting signal to the receiving signal is proportional to the displacement between the stationary part and the displaceable part of the transducer" It's not necessary to measure capacitance directly. Just phase angle. Which has the nice property that, as you move from one section of the comb to another, you're not going to get a jump. It's inherently monotonic.
- krisoft 4y ago> It's not necessary to measure capacitance directly. Just phase angle. Can that be done with analog circuitry or does the signal need to be digitised?
- KaiserPro 4y agoyou can turn capacitance into a waveform pretty easily, thats what the 555 timer does effectively, measure the time it takes to fill a capacitor. (https://en.wikipedia.org/wiki/555_timer_IC https://en.wikipedia.org/wiki/555_timer_IC its analogue.)
- MisterTea 4y agoThis is how a resolver[1] type encoder works. It's a rotary transformer with two stator phases at 90 degrees forming a sine and cosine output. The rotor has an AC current passed through, usually a few kHz, and the phase angle of the outputs vs the input is directly related to the shaft angle. There also exists a linear version called an Inductosyn which is similar to the calipers capacitive scale. They are absolute for a single rotation meaning if power is lost and reapplied, you still know the angle of the shaft (good for robot arms). This absolute positioning is not possible with a quadrature encoder. [1] https://en.wikipedia.org/wiki/Resolver_(electrical) https://en.wikipedia.org/wiki/Resolver_(electrical)
- throw0101a 4y agoSo what is some good equipment to buy (at various price points)? Has Project Farm (or someone else) done a ranking?
- theatrus2 4y agoThe entry price of a pair of Mitutoyo calipers isn't that high, and is the standard instrument pretty much everywhere.