Solar Panel Keeps Cheap Digital Calipers Powered Up

There’s no doubt that cheap digital calipers are useful, especially when designing 3D-printed parts. Unfortunately, cheap digital calipers are also cheap, and tend to burn through batteries quickly. Sure, you can remove the battery when you’re done using them, but that’s for suckers — winners turn to solar power to keep their calipers always at the ready.

[Johan]’s solar upgrade begins with, unsurprisingly, a solar cell, one that just fits on the back of his digital calipers. Like most of these cheap calipers, this one is powered by a single 1.5 V LR44 button cell, while the polycrystalline solar cell is rated for 5 V, so [Johan] used a red LED as a crude voltage regulator. He also added a stack of fourteen 100 μF SMD capacitors soldered together in parallel. The 1206 devices form a 1,400 μF block that’s smaller than the original button cell so that everything fits in the vacated battery compartment. It’s pretty slick.

Given their agreeable price point, digital calipers are a tempting target for hacking. We’ve seen a ton of them, from accessibility add-ons to WiFi connectivity and even repurposing them for use as DROs. Ever wonder how these things work? We’ve looked at that, too.

40 thoughts on “Solar Panel Keeps Cheap Digital Calipers Powered Up

    1. The cost adds up, but the main issue is finding them dead every time you pick them up to use them.

      If you use them multiple times a day they’re fine, but if like most of us you use them every few weeks/months then they’re just always dead by the time you next use them.

      1. Which is why I swapped out my digital ones for analogue ones.
        Cheap enough to keep 3 around the house. No more dead/leaking batteries. And I never really need more then .1mm accuracy anyhow.

          1. BS. I got good calipers which show the exact same number as my outside micrometer when measuring gauge blocks. Good calipers are true to at least 0.05, most to 0.01mm.
            Of course you can push the movable jaw to any value within 0.1 or 0.2mm if you press hard enough but that’s not how you use calipers…

          2. I’m with Daid re dial calipers.

            My cheap metric dial is indicated to 0.02 mm.
            At some point it’s not significant and you are recording noise.
            Depends on what ur measuring, in what posture and at what scale.

            Dial calipers are as accurate as digital calipers of the same quality. No batteries, yeah! Always work.
            You have to know how to work them.
            Which is ‘complicated’, like an automatic transmission.

      2. I’ve had good luck w/ Clockwise branded calipers. They’re accurate enough for me, inexpensive, actually fully shut off when you turn them off, and use CR2032 batteries.

    2. The problem with these cheap calipers is that many don’t actually turn off when you press the power button, they go into a sleep mode which drains the battery. This same behavior is common on cheap LED flashlights which have multiple modes, they go into sleep mode so when you reach for them when you really need it, the batteries are drained.

      The alternative approach many have taken is to install small sliding switch to disconnect the battery.

    3. Expensive? No.
      Annoying to change every DAY? Yeah.
      And it’s wasteful to be constantly replacing them too.

      I mod my cheap calipers to add a physical switch to disconnect the battery, because turning them “off” just seems to disable the screen.

    1. @
      0100010 said: “Easier to add an on/off switch.”

      Exactly! But the Chinese manufacturers of these cheap (and otherwise OK) calipers REFUSE to add a physical on/off switch. So I just remove the battery when I know I will not be using the tool again for days. Professionals do not have this option – so they should buy a known good product (German/Japanese is a good bet). Yes it costs more initially to buy a high-quality tool; but in the long term you will be much better off.

        1. A genuine Mitutoyo will run for a long time on a batter. Then run for a while longer with dim display. Knock offs drain at 10x the current, then don’t turn off correctly.

          Not a ‘better’ caliper then a Mitutoyo dial caliper.

          1. Exactly, Mitutoyo runs for a long time on an internal coin cell due to proper power management – most cheapo tools do not. And when the coin cell in the cheapo tool dies – it damages the tool due to coin cell leakage. All this could be solved by simply putting a physical on/off slide switch on the tool. But noooo – that would make sense, and stop planned obsolescence.

    2. You don’t need a physical switch. A MOSFET, two resistors and an I/O pin would solve the issue quite adequately. Cost: less than a cent. Probably equal to the profit margin these cheapo things have on them. Thus, no.

  1. I was thinking about manufacturers using a windup dc motor to power it but then if figured, why not turn the scale into a linear generator at no extra cost. pick up your callipers, move it in and out a few times to charge it, and then curse because the power died before you were able to take your reading.

  2. It would help if they had an actual on off switch that disconnected the battery instead of just turning off the display. You can find posts on the internet going back 20 years about this annoying feature. For my occasional use, I ended up going back to Vernier.

    1. I found that the iGauging Mitutoyo knockoffs have better circuitry that doesn’t seem to suffer from the off state issue.

      My two sets (home and office) are still on their original batteries, and I do use them rather frequently. I also have a set of the other brand cheap ones, and those drain in storage so I have to remove the battery when I’m done.

  3. Posted before. A gift and I don’t use it often but every time it was dead. Two 12-14 gauge solid wires coming out of the open button hole and a AA cell, it hangs off to the right by the yellow “scale” and fits in the case. It lasts the shelf life even after soldering to the cell. Cheapest 1.5volt source, always on hand. Tablet cells, which of many and voltage as well? Pay more for much less and good looks or ugly ready to work every time.

  4. A better approach might be a solar charger that connects to contacts on the caliper with pogo pins, and enough capacitance to provide a useful amount of run time.

    Or a switch. Or a bigger battery.

  5. Some 5+ years ago I bought a Mitutoyo. Before that, I wasted more money on cheap calipers then what the Mitutoyo cost (and no, it’s not a chinese knockoff). recently it’s low battery indicator turned on, so I guess I have to replace it somewhere next year.

    But I am looking for an extra caliper(s?) Absolute minimum requirement is an “absolute” measurement, so you don’t have to re-zero it after turning it on. A bit of a nuisance for the Mitutoyo is you have to pay extra for even the smallest things. Mine does not have a data output for example. A version with the connector costs extra, and the (official) cable is even more expensive then the calipers itself.

    I’m never going to waste money on EUR 15 calipers again. Quality is just too bad. I think you can buy a decent calipers for around EUR 50. The iGaging Origincal seems interesting. It’s also sold under different brand names and you can recognize it on “sharp pointed triangular” thumb rest and squarish battery cover.

    It also has an CR2032. And if you really want wireless charging, then putting in an LIR2032 and inductive charging circuit seems more sensible then a big solar panel

    1. I have the iguaging OriginCal caliper. Works for about a year on a battery whether you turn it off or not, never needs rezeroing – Just pick it up and measure. IRIC it was $40 from amazon about 5 years ago when I bought it.

    2. Adding absolute measuring capabilities like the mitutoyo ones isn’t an easy task. Cheap calipers cheat at it by measuring incremental changes but never actually turn the measuring circuitry off, just the display, so if you took the battery out and reinserted it, it would need zeroed. However the mitutoyo ones actually have a method for measuring the absolute position regardless of where it is when you put the battery in.

  6. i had this same problem of course. i think the better hack would be to design a new circuit that doesn’t eat batteries when it’s idle. that would only be worthwhile if you did the second hack, convinced the factory that makes the things to use your design. both hacks would be challenging but i believe are within the realm of possibility :)

    for myself, i was lucky that the indicator tape on the top of mine (human-readable on the top, machine-readable on the bottom iirc) already marked each milimeter. so i simply removed the electronic garbage and cut up a square of thin plastic from the recycle bin to serve as a window to indicate the position. used the original screws to hold the new plastic part on. given that i have to add 0.2mm of tolerance to everything anyways for my 3d printer, i can do a good enough job of just eyeballing the sub-mm precision.

    i have a dial caliper too but i like the simple slide better. and for whatever reason, i guess a combination of experience with the measuring and experience with my printer, i do a pretty good job these days. even when i have tight tolerances like for a friction fit component or so on, i typically nail it on the first printing. i guess the biggest factor is that i have an intuition now for what i’ll be able to fine tune with the x-acto or a file, and when i will want to use a rubber bushing (like an old innertube, cut up).

    i do wish i could simply just buy a better cheap caliper. on that note, i have the same problem with bike lights…i bought a whole series of astonishingly expensive cateye (japanese) and blackburn (californian?) lights that had poor battery life / poor rain durability / poor charger durability / poor mount to the bicycle. so for a long time i was building my own lights, with some success but maybe more hassle than i want. finally, 2024, i discovered the chinese lights on temu. wow. the cost is unbelievably low and the durability and battery life is as good or better and the mount was crappy but otoh was easy to replace with a 3d-printed bracket (which i successfully designed using my dumb calipers, getting a nice good friction fit on the first try). just an anecdote – sometimes china solves a nagging quality problem instead of introducing it!

  7. Never had any issues with this. Batteries on my cheap calipers usually last two years and I use them daily. I got 10 pairs around the house for reasons. All using 2032 batteries which I have plenty of.

    I do wish companies would stop using 2032 when possible and just change over to AAA if it needed to be small. That way I can use rechargable batteries. I know ML2032 exists but they are very expensive and don’t hold a decent charge when new.

  8. I suggest using an old calculator solar cell. They’re much smaller and provide an impressive amount of power for the size. Worked well enough on my calipers. The LED as a voltage regulator is an interesting idea.

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