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.

63 thoughts on “Hold, fast, and max features on a digital caliper

  1. @Hackius

    I have that callipers from dx and I don’t think it works. Tried it there, the screen does turn off when I short 1 and 4 I think but checking with a mm Im literally shorting Vcc and ground here. Pretty sure this one has serial output instead, there’s even a thread on the bottom of the dx page discussing this.

  2. I commented on the good quality of this tool; didn’t see that as trollish or too OT. Some people still don’t believe you can get anything quality from China, and brix would be shat if they saw me using my Chinese gage making parts for their Corvette, their kid’s school bus, or even a Ferarri. But if you need something more relavent to the hack: Those aren’t “hidden” features. That plug-in is an interface for SPC hardware and software, of which it has to be compatible with about 30 years worth of different ones. So he has accessed advanced user features. Still a worthy hack on a worthy tool.

  3. @element_leader

    Well,I said Hidden cause at time 0,there wasn’t any trace of it and at after there was. Also,I’m pretty sure the electronics that are in your mitutoyo or any other pricey calipers are made in china,maybe even in the same factory. Take for example DeWalt,those are good tools for sure,but they also make the canadian tire brand in the same factory.Most of the time,the only difference is the quality control.

    Follow me here:
    Dewalt get all it’s drill checked out,and the faile one are scrapped,this is a pricey thing to do but ensure that everything work and is reliable.

    CT brand get the same drills (different color, case) but the quality control test 1 out of 1000. It’s certain that there will be some scraps out there,but the money saved on QC is above the cost of a return. In layman’s terms, the consumer is doing the QC.

    All there is to it ;p

  4. After reasing the article, I’ve tried the same and have come to some new conclusions. And Im really happy that I’ve now upgraded my calipers.

    The clock line is already parallel witrh the zero button, so it’s not surprising that the data line, which is not parallel with any internal button, enables the hidden functions.

    Despite what BadWolf sais, there are 4 functions:

    Mode 1 (Default mode):
    – Relative measurements
    – Zero button sets to zero
    Mode 2 “H” / “F”:
    – Hold / Fast mode
    – Zero button toggles
    – Fast measurements
    Mode 3 “H” / “F”:
    – No visual difference between mode 2
    – Records minimum measure
    – Zero button toggles
    – Fast measurements
    Mode 4 “H M” / ” F M”:
    – Records maximum measure
    – Zero button toggles
    – Fast measurements

    Mode button switches to next mode if in hold or mode 1 if not in hold.

    Connector pinout (from inside to outside):
    – BAT-
    – #DATA (Mode button)
    – #CLOCK (Zero button)
    – BAT+

    #DATA and #CLOCK are 0V at rest. When a button is pressed (zero or mode button), one of these lines is connected with BAT+.

    Communication uses negative logic, 1.5V is ‘0’, 0V is ‘1’

    Data Message contains two frames.
    – Clock line 50us high signifies start bit.
    – Data is valid when clock pulse ‘1’ (0V)
    – First frame is a mode specific message.
    – Second frame is the value displayed on LCD.
    – Messages are as rapid as display updates (always slow if “H”).
    – The frame values are 8 times more accurate than the displayed value (1/800th mm, .00125mm)

    And finally (this is something I had known since I bought it): The circuit is ALWAYS on and ALWAYS measuring, even when turned off with the off button. To save batteries, take it out when not in use. Beware of this especially when leaving it in a fast measurement mode.

    (tomorrow I’ll post all the juicy pictures I made during the experiment)

  5. HARBOR FREIGHT CALIPER: Reading left to right as 1,2,3,4 I got that shorting 1 and 4 will switch between mm and in, 2 and 4 will switch between Hold, Fast Track Min and Fast Track Max, 3 and 4 will switch between hold and fast track.

  6. Be aware that the battery (+) lead is connected to the metal frame of the caliper (“positive ground”).

    There are several sites on the Internet detailing a computer interface (both to receive measurements and to change modes under computer control) and it’s important to note that this is NOT a “negative ground” system.

  7. I bought these callipers to help me make Sketchup models to drive my Mendel Orca Rep Rap 3D printer (when it arrives).

    Anyone any idea how we could link the callipers to Sketchup (or Blender, or anything else), to make model building easier?

  8. If you would like to avoid repeating lots of work others have done before on testing and hacking digital calipers, definitely check out the Yahoo group that has developed around the opensource OpenDRO project and shumatech.com’s digital read out products that use it.
    Link: http://groups.yahoo.com/group/ShumaTech/

    Also, here’s a brief article on digital scale features, protocols and modes: http://shumatech.com/support/chinese_scales.htm

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