How to build a circuit to handle a clocked data line

Discussion in 'The Projects Forum' started by vortexflow, Oct 4, 2010.

  1. vortexflow

    Thread Starter New Member

    Feb 16, 2009

    I am trying to interface a digital caliper with my computer.
    The digital caliper has a clock and streaming digital data.
    I am wondering if there is any simple circuit that would take in the clock line, the data line and compare the two in a way that the output would be a stream of a binary code.

    Clock (falling/rising) edge + state of the data line = 0 or 1 then do the same thing at the next (falling/rising) edge.

    I Have been reading about comparators but I am not sure if I am heading in the right direction.

    I would appreciate any help or pointers.

    Thank you
  2. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    What you'll need is a serial interface.

    Be aware that the communication protocol could be brand dependent as each manufacturer could be using its own in house protocol.

    Search Google for "digital caliper serial interface" and there are a few projects with detailed information, schematics and theory of operation.

    Perhaps this one(for gauges typically made in China):

    Digital Read Out Caliper Gauge
  3. jpanhalt


    Jan 18, 2008
    Here is a project on this forum:

    It also gives a link to Don Lancaster's project for Chinese imports.


    Edit: Note that Mitutoyo uses two protocols. One requires a request bit to be sent; the other does not. I suggest you start with the brand of caliper you have (if that can be determined). The Chinese imports all seem to be similar (see the link to Don Lancaster). Then check that manufacturer's site for specific information.
    Last edited: Oct 4, 2010
  4. vortexflow

    Thread Starter New Member

    Feb 16, 2009
    Thank you everyone for the pointers.
  5. Maris

    New Member

    Dec 13, 2010
    I did exactly what you wanted to do using TI's MSP430 development board Launchpad. You can find source code and detailed description in my blog post:
    Interfacing TI MSP430 Launchpad to Digital Caliper

    There are two lines from caliper - clock and data. On every clock pulse you need to read data line bit. 24 bits in total and put those bits together to make integer. Then send them to PC using serial. Launchad costs only 4.3$ and that's almost all you need - so, you can do it very cheaply.