Supercharging Your Digital Calipers


A dead battery in your digital calipers usually means a trip to the store for a new button cell. Not for [Trevor]. His hack substitutes a super capacitor, guaranteeing you’ll never need to rummage around for one of those pesky watch batteries again.

These calipers require only 20 seconds to reach a full charge that can last for a few days. Better still, [Trevor] designed a simple circuit with a voltage regulator at the end of the cord to allow charging via USB: just remember to flip the switch from “discharging” to “charging” mode. Although this is a fairly straightforward hack, its design is impressively tidy. The super capacitor fits perfectly at the end of the display and slides along with it, keeping it away from any important printed numbers. If these are the same calipers everyone seems to have these days, it looks like it may still fit in the provided case, too.

If you’re looking for more ways to beef up your calipers, try upgrading them with a Bluetooth module.

56 thoughts on “Supercharging Your Digital Calipers

  1. I wonder why they do not integrate some kind of energy harvesting, charging a smaller cap by sliding the caliper open or so… perhaps because it takes ages for a battery to run empty, but still.

    1. I just go to Lowes and pickup a pack of 2 everready 12v garage door remote batteries.

      There are six 1.5v button batteries in each one for a total of 12 button batteries for about $4-$5.

      They are a little smaller than the original battery, but i just wedge a piece of paper between the battery and the holder and close the lid.

      1. Okay, but instead of doing that you can simply buy LR44 for about 10 cents a piece in bulk on ebay. You know you’re going to need them every so often so you might as well just order ahead of time.

    1. “wouldnt going to the hardware store for a battery every 6 months be easier”

      Not really easier, unless you automate the reminder using Slack or a calendar, and then use IFTTT to send yourself a reminder whenever you dropped into the store for something else.

      It’s far easier and cheaper to use AAA. I just got BACK from the hardware store, needed to use my calipers, and the battery was dead. I actually found this article searching to BUY hardware that takes AAA by default.

      1. Huh? AAA for a caliper? It’ll have to be HUGE to fit one.

        Who goes to the hardware store to buy batteries in this day and age anyway? 10 cents a piece for LR44 in bulk on ebay, delivered.

  2. These calipers really need to be redesigned with a real on/off switch that disconnects the battery, instead of the current button that only turns off the display.

    In the meantime, I remove the battery after every use. It’s a pain putting the battery in and taking it out every time I measure something. But it’s less of a pain than going to the store and buying the overpriced batteries.

    1. I took mine apart, soldered wires to the battery terminals, put a AA holder and added a real switch like you suggest. It works great. The battery will probably self discharge faster than I use it with the calipers.

      1. I think he was talking about reading the scale/slide on this one. This low-tech method still works, but it’s less precise and I don’t really trust these cheap plastic calipers to have accurate markings.
        Nevertheless, is the method I’ve been using for the last months on my one, did not bother to put a fresh battery in.

        1. i have a total of 3 of those, and use all of them more then i’ve ever used my digital calipers. but i don’t need any more than around 1mm precision on most of the things i measure.

      2. I don’t remember anyone mentioning dial calipers specifically.

        I use Vernier calipers – no batteries – no dials. Just simple addition and the ability to read lines on a scale are all you need.

        1. I have a vernier caliper, but since it is read in fractions instead of decimals, i hardly ever use it. I can never remember if that is a 64th line or the 32nd one. But I do keep it in my to mobile toolbox for emergencies. you’re right I never have to remember batteries for it..

    1. I can read one fine and think that’s an unnecessary burden, additional so if you want to convert to a fraction. You simply avoid the junk ones that burn through batteries. A decent chinese digital one is still less expensive than a decent dial caliper.

  3. It is a cool mini hack! But much more trouble to charge them every couple of days. My calipers have been running on the battery they came with for a year. And they also came with an extra battery, which fits in a slot in the case, which slot actually holds two of those coin cells. Buy some extra –

      1. 3-500$? I use Starrett, which is the made in the USA caliper which originally Mitutoyo copied (or competed with, depending on your outlook) and even they are about $200 for the 8 inch version. The Mitutoyo is about equal in build quality, but i prefer the feel of the Starrett.
        By the way, in either one, a battery lasts at least a year, closer to 1.5, with heavy, all day, every day usage. Those $35 Harbor Freight calipers are worthless. Impossible to adjust the gib strip (the brass wear strip that, if not adjusted right, destroys accuracy), they have terrible build quality, terrible feel, and break randomly.
        Unless you only use the thing once every 6 months, blow a few extra bucks and get a $115 Starrett dial caliper, or a $175 Starrett ‘global’ edition (made in China, but still passing starrett quality control)

    1. Mac, I was getting ready to say the same thing.

      And x3n0x $300 to $500? I don’t know where you are shopping for calipers, but they are easily under $150. I’m not saying that’s cheap, but they are reliable.

      I used to use the cheap calipers, but I just got tired of picking one up in the shop, and they would be dead. They always seemed to be dead when I was working. Now I just have Mitutoyo calipers. I haven’t replaced a battery an any of them. I’ve had one for 6 years.

      I understand using the cheap ones for hobbist, but if you need them for a job, you are just wasting your time and money.

  4. What a great idea. I might try this with my cheap pair of digi’s and then if successful move on to my Mitutoyo’s. When you have as many as I do it’s really a chore to keep enough good batteries around for all of them.

    A couple of thoughts:
    1. What about replacing the switch and charging port with a 2.5mm mono headphone connector with an internal switch like this one: ? Wire the tip positive and barrel ground. That way you can wire the caliper circuitry to the switch contact and the cap to the tip contact. When you insert, it automatically disconnects the caliper from the cap and charger.

    2. I wonder if one could combine the charging port, supercap, and contacts into a replacement battery cover. A little 3D printed housing could hold all this and snap in where the cover used to with some contacts that hit the original contacts in the battery tray. Now you didn’t even modify the calipers…

  5. Or you could just buy some real calipers instead of wasting money on batteries every 2 weeks. Mitutoyo calipers last 2 years constantly on, on the same battery that the cheap ones use.

  6. “so watch out grammar trolls”. Hark! Someone is calling me!

    From Josh’s article: “If these are the same calipers … it may still fit in the provided case” /These/ is plural and /it/ is singular.

    I would’ve let it slide, except that I was challenged. :-)

    1. My title should probably read “recovering English teacher;” alas, you are correct.

      I did, however, read the “let it slide” part of your comment with a tickle of groggy, half-awake gleefulness hoping it might be a subtle pun.

  7. $5 battery?? Those calipers often use cr2032 battery, which costs about 25 cents a piece, if you buy 100 pieces price drops to 18 cents. And that’s for brand name like Panasonic. I like this hack from fun&learning point of view, but considering time&parts invested it is not very economical.

    1. absolutely. placing the primary coil on the bottom of that tools drawer, or on the pegboard, would be great. nothing to remember except to put your tools away when youre finished with them.

  8. Ok, now the calipers are rechargable, but look ugly as fuck.
    Someone needs to 3D print him a case, that includes the capacitor and has some solar cells in it, since the cable is even uglier than the calipers with the cap sticking out. Futhermore the cable won’t last long.

  9. Buy a real pair of digital calipers and the batteries will last years. Also, you won’t have to zero every time you close them, and you can actually trust the numbers they read.

    Cheap digital calipers are trash.

  10. I can’t believe some off the comments I read here like “Those calipers often use cr2032 battery” no they don’t , “it’s really a chore to keep enough good batteries around for all of them” and “Or use a Mitutoyo”. Here is a super tip for all of you: Have you ever heard of a site called ebay ? just search for “100 lr44” and you will get plenty of deals for one hundred of these little batteries for just around 7 US dollars. There you go, all your problems solved, and you won’t have to run to the store in the middle of your big project and pay 5 dollars for a single battery.

    1. If that’s too much work/time, go to the dollar store. Usually they have many kinds of watch/button/coin batteries in multi-packs for dirt cheap.

      Alternately, the last time I needed button cells, the dollar store didn’t have them on their own, but they did have generic “window alarm” units (piezo, magnet, batteries) for $1 per each. I read the back of the packages to make sure I was getting alkaline button cells (instead of the cheapola ones), and then bought several. Each had 3 button cells, and cost $1. Hard to argue when the grocery store wanted $7 for a pack of two button cells… So I got three sets of three button cells, plus some magnets, leds, and three piezo buzzers. Not bad at all for $3, total.

      Sure, they’re not silver oxide, but I only have to remember to change them out every 6 months (or sooner if necessary), and I’ve come out way ahead.

    2. That’s exactly what I did; bought 100 LR44 batteries on eBay for around $8. YEARS AGO, and still have like half of them… And I’ve got half a dozen calipers to feed! (Plus laser pointers and all sorts of other crap that takes LR44s)

      I would only use buying dollar store tchotchkes as a last resort, because god knows how many times someone’s fooled around with it and run down the battery!

  11. Ok people:

    1) For everyone saying to buy a “real” digital caliper, this site is called HACK-a-day, not product_review-a-day.
    2) For everyone saying to just buy batteries, this site is called HACK-a-day, not how_to_fix_my_tools-a-day.

    Very cool hack. One suggestions: mod the switch so that when it is in “discharging” mode, you can’t plug in the charging cable, thus protecting the caliper circuitry.

    1. Yeah there’s some real snobs here, not everyone has spare money to spend shitloads on a digital caliper which has a resolution and preciceness far in excess of anything they’ll ever need, my £10 one does me fine and I only need to give it a new AG13 battery perhaps once a year.

      1. I agree with you. The perfect tool is the one that fits your need. And a $300 caliper will never fit my need unless I am a professional machinist. I rarely use mine over the 100th’s precision.

  12. I bought ten 10-packs of Chinese batteries from a US-based eBay seller for a total of around $8 several years ago. I still have more than half of them… Sure, they don’t last as long, but it still beats going to the pharmacy and buying a pair of Duracell ones for like five bucks.

    You can never have enough of these things! I’ve got like half a dozen, including a 12″ one I got for $2.95 thanks to a pricing error on Amazon Marketplace. :]

  13. I never really use my digital calipers anyway. After a bit of practice, reading the old fashioned Vernier Calipers is just as fast. If you NEED the “accuracy” of a digital caliper you should probably be using a micrometer (Yes, indeed, very expensive). Many of the cheapo Chinese made digital calipers are not very accurate.

    I like the idea of this hack and I can relate to the problems. I just have my doubts the cap wouldn’t get in the way when holding the calipers for a measurement. (Especially when measuring things on a lathe, I would probably want to be holding it right where that cap is)

  14. I think with auto-off and soft-off devices it can still be the damn drainage that empties the batteries, so a mechanical switch is probably a good idea.

    Another idea is to make some sort of magnetic clamping, you know like apple used, but for a batteryholder, that way ‘inserting’ a battery and removing it again is quick enough to not be a hassle as it is with all the plastic slide caps and such we use now, and you get the easy backups option when you make more than one batteryholder to clamp on..

    1. My idea… Put a normally closed reed switch in series with the battery. On the place you store your calliper, have a magnet somewhere suitable. So whenever the calliper’s hung up on it’s peg, the magnet disconnects the power, so it’s properly off. When removed, it flicks back into life again. A reed switch should be small enough to fit in the casing if you’re lucky.

  15. Walmart is open 24/7, but that’s a 48 mile round trip and I discover the battery is dead after the the local small town hardware store closes at 6 PM. For my post apocalypse shop ;) I intend to get dial calipers or dig through mom’s garage for the veneer calipers that belong to her dad.

  16. I turned the button-cell battery compartment into a switch itself. Take a strip of that indestructible and stiff clear packaging plastic they put everything in these days. Open up that little slide where a USB data interface cable goes (the plastic port-cover slide that is just on the far-side of the battery compartment). Cut the clear packaging plastic to fit the width of that data-port, then push it in until it goes between battery and contact. Bend-up the section hanging out and put the data-port cover back on (the tension of the plastic strip keeps that port cover from popping out easily). Cut off excess plastic strip. I have 2 bends in that plastic strip, one for when it’s on, and another for when off (replacing the data-port cover each time). When you need to use it just pull that clear stiff plastic strip out far enough until it turns on, slide it back in when done. You do have to slide that little data-port cover off each time to turn it on and off using the plastic strip, but that’s easier than fumbling with where to put the battery each time. I tried with putting that plastic strip under the edge of the data-port cover, but that strip then got in the way of where my fingers are, and didn’t like it as much, but it would be much easier to slide the switch-strip in and out without having to take that little port-cover off each time. You’d probably have to tape-down that little port cover too, the switch-strip making it not seat as tight it falls out easier when the strip is under it, rather than between it and the display housing.

    But if you don’t want to bother with that, I get 50 of those LR44/AG13 batteries from ebait for about $2.25-$2.75. I use them in so many things (timers, temp-gauges, lasers, etc.) I like having excess around at all times. It takes a couple weeks for them to arrive from China but the price is worth the little extra wait. Throw them in the fridge for storage. One flat of 50 cells can last years.

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