Hold, Fast, And Max Features On A Digital Caliper

While adding an RJ-11 connector to his digital calipers [BadWolf] slipped, shorting out a pin and accidentally discovered new features. He intended to add a port for reading measurement data electronically, but after the slip-up an ‘H’ appeared on the LCD screen and the measurement was frozen at the same number. At first it seemed like he may have killed the device, but this is actually a hold function. A little bit more playing around and he discovered that a combination of button presses can also enable a fast function which speeds up the rate at which the display changes its reading. There is even a max function that only updates the display if the reading is higher than any previously displayed measurement. These are nice features which he uses by connecting a momentary push switch between two of the output pins, details we gleaned from the annotated video after the break. He doesn’t say which pins work for him, but we’d bet one of them is the ground pin on the port, and the other is one of the two data pins. Do some investigating with your own calipers and let us know what you find in the comments.


67 thoughts on “Hold, Fast, And Max Features On A Digital Caliper

  1. Sometimes those “features” are masked off because it does not work correctly. Or because that same uC was used in another design. Or it is something the engineer felt like putting in for test purposes in a later design. They are not necessarily trying to cheat you.

  2. Tried it, from my brief experimentation, there are 4 modes (mind you, my calliper is a bit different, letters are shown not at the top of LCD, but on the left side):
    1) regular
    2) fast function/hold
    3) min hold
    4) max hold

    To switch from mode 1) to 2) short pins 2 and 4, while calliper is in hold mode(H letter on lcd), short pins 2 and 4 again, this will put calliper in mode 3), do it again if you want to switch to mode 4). If calliper is in “measurement” mode (showing INC on LCD) and you short 2 and 4, calliper goes to mode 1).

  3. Now this is a nice simple hack. Just did this to a set of calipers using a tiny momentary switch from a bust mouse, It works well. The control wires are the easy to solder and access ones right under the cover and the ones you want are the 2nd and 4th when looking at the front of the calipers as normal. Happily it stores your settings when powered off so only issue is that you need to turn the “fast” mode off to calibrate/zero.
    Well done!

  4. The slower refresh rate is probably to save power. As to not installing the other features, there are probably only a couple manufacturers of the ICs used inside calipers.

    They probably don’t activate the extra features because the extra switches may not fit in the internal volume of the designed case or they are trying to get a lower selling price to undercut competitors.

    I work for a major telecom equipment company in R&D. You would not believe all the features that we cut out just because the company does not want to support them, or we have to rush a design out the door.

  5. good deal! I need to get a digi one anyway. I’m to lazy to read the manual ones, and digi is much faster, plus I’m practically blind so the big lcd is easier for me. I wish there were more photos of the insides, it would help but whatever. since you’re here bad wolf what exact make/model is this?

    side note. this is the first time I’ve seen a hack hosted on facebook! at first I thought I would have to be signed in to see it, glad to see that’s not the case.

  6. @ Brad
    thanks for the keyboard ;p it’s a Steelseries Mercstealth,best keyboard i ever laid my hands on ;p

    It’s one I’ve ordered a long time ago from Princess Auto. It has absolutely no model number or company name. but here’s a link to it on Canadian Tire:


  7. @jkdrum – I used to work for a major test equipment manufacturer, and several of our models had serious upgrades that consisted of accessing a settings mode through the front panel, and turning on the options. I’m talking $30K worth of “soft options”. It became a game of customers trying to find the codes, and engineering changing them.

    There were some real ethical questions involved, like “Our records don’t show that he should have this $10K option, do we turn it off? Are our records correct? Are we going to be charged with a felony for stealing functionality from him?”

  8. “I like that merc stealth in the background – I’ve got the same one.”

    “psh, forget the hack, nice keyboard!”

    “thanks for the keyboard ;p it’s a Steelseries Mercstealth,best keyboard i ever laid my hands on ;p”

    Good to know I’m not the only one who thought the keyboard was cool. does it light up inside, by any chance? where can I get one?

  9. I thought mine was a battery eater, now I know. I don’t use it very often , it’s always dead. My first hack will be to put a AA cell set on it, to hell with sleek tiny BS.
    A laptop should run for a week. Portable CD for 25-50 CD’s. Camera for a weekend tour away from it all. This should run for a year.
    It’s just a racket with the battery folks when they tiny out anything. You pay more for less. If a new model uses less power, then wimp out the power supply!

  10. Just tried it on my “Insize” 6″ digi cal. Yup works just the same (pin 1 and 3 i think from left to right). I wouldnt doubt if there is a Chinese manufacturer that sells these as “buy 100k units, and we’ll put your name on it” type of deals. Great hack/discover! Tho I’m old fashion for being so young, so I still trust the ol’ dials much more than the digi’s.

  11. Sweet. Worked a treat on my no-name caliper I bought here in Sweden years ago. The fast update is a very welcome upgrade. Only problem is that I have already soldered an AA battery to it and then taped the sucker right over the cover. I’ll have to do something about that.

    Oh and btw, adding an AA to these things is great, haven’t changed the battery in years and I’ve forgotten to turn it off for days plenty of times.

  12. My set has the battery door that opens by sliding to the right instead of down, and the mm/inch button is over the zero button instead of the power button, and it doesn’t work for it.

  13. I bought one of these off ebay a few weeks ago. If you look at the intructions they include diagrams for the upgraded model which has a ‘mode’ button. I’m assuming you’re just implementing this switch?

  14. Looks like mines a little different, the 4pin port is just a serial port (see earlier hackday post of someone talking to it with a micro). The mode button that exists on the higher end models is still in my model too, theres just no hole in the case for the button but the button contacts still exist on the pcb. All youd need to do is cut out the square and add a button.

    Heres a pic:


  15. Interesting.

    On mine, Pins 2 and 4 cycle through a few modes.
    Short once and you get hold (H displays). Press zero in this mode and I get “INC” displays and it’s in fast mode. Zero toggles between H and INC.

    If you short 2 and 4 again, it goes back to normal mode.

    Now from normal, if you short 2 and 4 twice, you still get H. There is no display change between mode 1 and mode 2. The display is held. Press zero in this mode and “INC” shows and the display only shows the minimum reading. Hitting zero hold, and hitting it again resets the display to the current position, again in minimum mode.

    If you short 2 and 4 three times I get “H” and “SET”. The display is held. Hit zero and you get “INC” and “SET” and the display shows the maximum reading. Hitting zero again holds the reading and again will reset the display to the current position and return to maximum mode.

    Shorting pins 3 and 4 seem to be the same as hitting the zero button.

  16. Hmm turns out that extra button I discovered isnt a mode button, just another duplicate mm/inch button. Guess its impossible to get the extra functions with the caliper with the serial port

  17. @Bill D. Williams
    True, they’re no Mitutoyo, but I’m sure they’re more reliable than a tape measure or ruler.
    We’re not talking about a shop making parts to spec here, just hobby work =]

  18. @Bill D. Williams & Spork
    I’m actually a mechanical engineering tech,and we compared those to $200 mitutoyo ones, and they hold the same tolerance if you don’t play too hard with them. Also,don’t forget that a digital caliper,whatever the brand is 90% of the time a 0.005″ precision due to it’s manufacturing process.
    If we look at 90% of the regular milling jobs,they are std +- 0.010″ so we’re good to go ;p

  19. I have a similar looking set of calipers

    Branded “Powerfix(R) ELECTRONIC DIGITAL CALIPER” on the ruler.

    “Model No: Z22855
    Version: 07/2008
    Battery Type: 3v-CR2032
    OWIM GmbH & Co. KG
    Stiftsbergstraβe 1
    D-74172 Neckarsulm”
    On rear.

    Clearly similar construction to the others, Shorting pins 2-4 enters additional measurement modes like Mike describes but the lcd dislay does not appear to have any of the additional symbols.

    Great mod though. I will find a micro-switch and add a port. The pin spacing looks like standard 2.51mm to me (I would measure it if I had a second caliper set!) I reckon that female headers will fit in there perfect assuming that there is data lines out…

    Great mod!

  20. @Bill D. Williams No tool is garbage

    The tool either is good enough for the job or not good enough for the job. These cheap digital calipers are a huge and cheap upgrade on using a ruler. Would I use them to build a spaceship? No.

    I take it the only people who come into your shop are spaceship builders right? And every single customer you have demands a sub 1thou tolerance on everything right? Right?

    Thought so. Allow me to laugh my butt off at your suggestion that I should spend $10 the amount of money I did and gain absolutely nothing from it.

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