Cheap Caliper Hack Keeps ‘Em Running Longer

Many a hacker is a fan of the cheapest calipers on the market. Manufactured in China and priced low enough that they’re virtually disposable, they get a lot of jobs done in the world where clinical accuracy isn’t required. However, their batteries often die when left in a drawer for a long time. [Ben] was sick of that, and got to hacking.

The result was a quick-and-dirty mod that allows the calipers to be powered by a AAA battery. The average AAA cell has 5-10 times the capacity of the typical LR44 coin cells used in these devices.

[Ben] whipped this up with an eye to making it work rather than making it nice, so there are some shortcuts taken. The battery housing was 3D-printed on the lowest-quality settings that were viable, and it’s held to the calipers with hot glue. Similarly, bare wire ends were used instead of proper contacts, taking advantage of the battery being crammed in to make a good connection.

It’s a hack that will likely save [Ben] much frustration, as he’ll now rarely open his drawer to find his calipers dead. However, one [Pete Prodoehl] suggests another useful trick: store the calipers in the closed position with the lock screw tight to save them turning themselves on accidentally.

Whichever way you go, you’ve hopefully learned something today that will keep your cheap calipers working when you need them. Next, you might consider hacking them to capture data, too.

48 thoughts on “Cheap Caliper Hack Keeps ‘Em Running Longer

  1. Because the micro-controller from those cheap callipers isn´t optimized for low-power, or lacks the necessary power states, they drain the batteries all the time. All they do is switching the LCD off, which does not bring much.

    This hack with an AAA battery isn´t bad but it is bulky and comparatively heavy. Adding a switch is better: no battery casing protruding on the side, no unbalanced weight. One must just not forget to switch the callipers off :)

    1. Switch – hmmm – how about a momentary press switch, and a supercap/tantalum which will keep the callipers running for [5] minutes. Then you’ll never forget, which solves the Human Interface issue.

      1. The reason they don’t turn off is because the calipers remember the last position value – they’re actually always measuring it even when the display is off, so you don’t lose your last zero offset. It would be highly annoying if you lost your reference because you didn’t press the button every few minutes.

        That’s one of the annoying things about most kitchen scales. They’re too fast to turn off and reset the tare

    2. This is exactly the problem – it’s the drainage, not the small battery – and what I did to rectify this 5 years ago.
      There was enough room in the casing above the battery compartment in my digital calipers to put in a SPST 1-channel DIP switch. The battery now lasts for years at a time and is a very discrete modification. I just cut away the casing to fit using an Xacto #11 and solder/sodder the leads. Here it is:

      1. I just pull the battery out of mine, the case can hold heaps of battery in it, so it is trivial to put one in while I need it, and store it the rest of the time.
        But mostly I prefer the purely mechanical caliper anyway, so the battery one is generally off for a very long time between uses, if I actually liked using the digital one as much I might put a switch in…

      1. I have tried, but with little success. The charge is low and the cap seems to drain current even faster than the circuit.
        Plus, when the voltage drops, the measurements start to drift A LOT.

        I end giving up on them and bought an Asiemeto caliper. Isn’t that expensive and has a cr2032 battery that has way more capacity than those “LR44” that come with the chinese caliper

  2. I just take the battery out after use each time (as mine came with a case which they are stored in)

    I do wonder if the little battery compartment lid might snap though one day from overuse.

    I have also upgraded a set of kitchen scales with 2x AA batteries because the CR2032 coin cell lasted only a month. This was done by taping on a 2xAA standard battery holder. Now I think about it a nice upgrade would be AAA, maybe one day….

    1. That’s what I do and yes one of the tabs has broken off after years of use – maybe 15 years of sporadic use – so certainly viable – these days I don’t bother putting the cover on the battery still sits in there and I pop it out when I’m done – I do intend to add a switch one day

    1. Yeah, I really can only shake my head looking at all those comments “switch, batterypack, taking battery out, …”. LOL, just don’t buy 10$ calipers. They’re not worth it.

      Buy a used one if you can’t afford the new ones. As I’m in the EU, there’s many good brands out here like Mahr, Tesa and many more. Mitutoyos get copied a lot, not easy to get a genuine one. Paid 40€ for a used Mahr and 25€ for a used Tesa.

      I use both of them daily and the batteries last for 2 years or more.

      1. Same, I do work on the lathe, I can’t afford an untrusty caliper that drifts when the battery is low.
        Mitutoyos here where i live cost about 300usd and made in brazil… (if i’m gonna pay 300usd or more better be made in japan)
        I ended up buying a 70usd Asimeto and battery last forever.

    2. Yee my Mitutoyos last seemingly forever and I use my 8 inch as much as possible. Still have an 18inch Harbor freight for the big stuff since I couldn’t justify spending that much for hobby projects

    3. Same here.
      I had some cheapo calipers, had the battery drain issue.
      Replaced them with some Wiha composite calipers, thinking “made in Switzerland”, must be good. Big mistake. Not only were they flimsy (not rigid), but they drained batteries as well.
      Now have some Mitutoyo Absolute Digimatic, and they are much better, and don’t drain batteries! And I didn’t pay all that much for them on Ebay either.

  3. The cheap ones at harbor freight ( I use them at work in a machine shop) all have an off button. I have the 6″, 8″ and 12″ and they all have a power button and I think I paid less than 30$ a peice for them.

    1. The problem is they still draw a significant amount of power when you press the off button, and they’re crappily made. I have 4 pairs of the same 6″ Harbor Freight calipers here and they’re all wobbly and have jaws that are visibly far from parallel, all on top of running through a battery every few months.

  4. On mine i put a little loop of kapton tape around the battery compartment to create a tab. Between uses I can just grab the tab, pull the compartment, turn it 180 degrees and slide it back in. Free on/off switch.

    1. I went thru the time wasting process of trying to find a non-fake Mitutoyo digital online, couldn’t find one with any degree of certainty and so I purchased a much cheaper second hand dial Mitutoyo vernier (ebay) which I still use every day.

      Beautiful Japanese quality, smooth as silk.

    2. Here is the underrated comment. I initially bought a pair of digital calipers to make life easy for a repetitive task but I have since discovered that using the dial caliper is, at least for me, more accurate and needs far fewer batteries.

  5. I went to a college where every engineering student had to take a machining class, taught by a crusty old ex-tool maker.

    One of the first things we learn is how to use the precision layout tools – calipers, scriber, etc. And one of the first thing that was drilled into us was that you *never* leave good calipers closed. In fact, you wipe the jaws of the calipers before using them, close them and verify the zero, then take your measurements, and you always leave a small gap so that debris and swarf don’t etch up the precision ground jaws when you are done. We’d also were trained to brush off any precision mating surfaces – such as jaws on a mill, parallels, collets and spindles, the cam lock mechanism on a lathe chuck, granite surface plates, etc. It is amazing how sensitive human fingers are and that you can feel specs of dust on these surfaces.

  6. I literally did this to a pair of calipers a couple of days ago. For some reason the battery dropped in and out, and they were useless. So far, the AA powered calipers are working great!

  7. Cheap Chinese Vernier scale callipers are no better. They rust like crazy, and the numbers immediately rub off. I believe the Chinese get the bulk of their industrial equipment from Japanese manufacturers.

  8. Here’s another example to me where an electronic device is less useful that it’s predecessor; the dial indicating caliper. Rather than sign up for a lifetime of buying batteries and frustration, just buy the mechanical caliper and have something that always works. It’s a green solution too. There’s also the option of using the veneer caliper to .001” if you learn how to read clever scale on the side. It’s kind of cool how that sliding scale works to get you the last digits.

    1. I wouldn’t necessarily say less useful – the electric ones have uses you just can’t get out of the mechanical (like direct data point capture to feed into your cad model), and potentially higher precision in the same footprint too.

      That said I am a mechanical one by choice too, good dependable tool, that you can even make one yourself from scratch by hand easy enough and still get ‘precision’ measurements – so its generally trivial to repair them if they ever break, where the magic smoke lets out not much you can do…

  9. I did this years ago. Quick and easy no 3D work at all. AA cell naked no bigger than what is featured here, it fits in the case as well. I’ve replaced the cell once with a used one no less to start. 2 pieces of #10 or 12 solid house wire in that same location soldered into that little cup. At the battery end, diamond wheel clean both ends of the cell first. With my trusty Weller gun and fluxed solder one second is all it takes to build up a fat blob taking most of the heat away form the inside. Same with the ends of the wire, sweat together no sweat. Done.

    We have a couple of micrometers in the piano shop for gauging wire and center pins. People always want to “close” things except the pipe clamps, the sliding ends get caught in the stack and get lost.

  10. I just pop out the LR44 battery and place it into the case along with the calipers. While it is slightly inconvenient, my caliper use is infrequent. BTW, the calipers are also unstable when florescent lights are nearby, as I discovered at my workbench which has florescent lights about four feet above.

  11. This reminds me of a project I have in progress: combine an nrf52811 micro from a key tracker with one of my data-port calipers, for direct dimension entry over BLE. One of these days I’ll finish it…

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.