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.


  1. wvdv2002 says:

    Isn’t it much more handy to have a ‘hold minimum value’ function for a caliper? If you want to measure the diameter of an object for example?

  2. Hackius says:

    Oh man that fast mode is something I’ve desired for a long time

  3. Khordas says:

    I really hate the way manufacturers do this thing where they disable features in order to be able to sell an ‘upgraded’ model to you later. Good thing there are hackers.

  4. jkdrum says:

    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.

  5. Brian says:

    Good hack! Looks like it might be a good place to use a surface mount switch like the ones used to open CD drives. I could really use the fast mode.

  6. Brian says:

    Researching further it seems like you could add the switch to the cover and have spring contacts to the connector. This way you could slide the data cable in the slot. Look at this hack for a better visual http://www.robotroom.com/CaliperCapacitor.html

  7. Mike says:

    It is Pin2 and Pin4 (i have the same Digital Caliper)

  8. tromano32 says:

    A nice surface mount switch on top would be a good upgrade and try to hide all the wires inside.. maybe even use magnet wire to save space…

  9. meh says:

    Oh awesome. I coincidentally ordered these exact same calipers online a few hours ago before i read this! Happiness! ^_^

  10. X-log says:

    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).

  11. TheBadWolf says:

    I am featured ^^


  12. I had done some good research for this subject a time ago. I had reverse-engineered the protocol for 2 different Chinese-calipers, one is absolutely similar to this. Check it out:


  13. JC says:

    Maybe I’m old-school, but I really prefer the dial calipers. It’s nice to see the rate of change on an analog device.

    Nice hack though!

  14. Marto says:

    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!

  15. octel says:

    Is the fast mode less accurate in any way?

  16. TheBadWolf says:

    @ Octel
    Absolutely not,it just change the refresh rate.

  17. JFS says:

    Scott Shumate made a nice digital readout using these calipers (and others). There is a wealth of information on the protocol, and connections on his website http://www.shumatech.com, and the Yahoo group http://groups.yahoo.com/group/ShumaTech/

    No affiliation, other than I have one that I use on my milling machine.

  18. Techmonkey says:

    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.

  19. paul says:

    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.

  20. thebulbguy says:

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

  21. brad says:

    psh, forget the hack, nice keyboard!

  22. Brian says:

    Anyone know the effect of fast read? Perhaps it shortens battery life?

  23. Bob says:

    No luck with my Chinese caliper. 1 and 4 cause a zeroing, but that’s it.

  24. TheBadWolf says:

    @ 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:


  25. Hackius says:

    Here it is on dealextreme: http://www.dealextreme.com/details.dx/sku.2306

    Seems to be that exact caliper model. I just ordered one and will report back.

    My guess is that fast mode will eat your battery faster.

  26. TheBadWolf says:

    @ Hackius
    not the same but very close indeed!
    Can’t wait to see if it works!

  27. Bob says:

    Can anyone compare these to a “normal” caliper to see if the accuracy is up to par?

  28. rallen71366 says:

    @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?”

  29. TheBadWolf says:

    @ rallen71366
    where did you worked at?

  30. Jordan says:

    “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?

  31. echodelta says:

    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!

  32. David says:

    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.

  33. sneakypoo says:

    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.

  34. zool says:

    looks like a mouse button

  35. Jake H says:

    This is EXACTLY the sort of thing I come here for!

  36. TheBadWolf says:

    @ jordan
    Keyboard is from FutureShop.ca

    Mouse button it is,scavenging is my prime hobby

    @Jake H
    Happy to hear this

    Guys,I’ve updated the post,here it is now:


    Enjoy and I STRONGLY encourages you to create an account on hackhut,it’s freakin amazing!

  37. cboy2us says:

    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.

  38. paul says:

    thanks BadWolf! We’re tryin hard to be what hackers want.

  39. vtl says:

    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?

  40. vtl says:
  41. hammy says:

    @wvdv2002 maximum level would be handy for doing internal pipe diameters etc

  42. vtl says:

    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:

  43. Bill D. Williams says:

    Trust me – those calipers are garbage. If anyone came into my shop using them, I’d laugh my butt off.

  44. Mike says:


    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.

  45. vtl says:

    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

  46. Spork says:

    @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 =]

  47. TheBadWolf says:

    @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

  48. Justblair says:

    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!

  49. Garbz says:

    @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.

  50. element_leader says:

    That looks like a caliper I have. It has been used daily in an industrial environment for over 2yrs. Calibration checked by outside firm every 6mo.

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