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How to build a micrometer

Discussion in 'Electronic Design' started by Ben Nguyen, Sep 15, 2003.

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  1. Ben Nguyen

    Ben Nguyen Guest

    Im looking for ideas to do for a school project and came up with
    a digital micrometer.

    Does anyone know whats involved? I want something challenging, but not
    something impossible!

    Thanks!
     
  2. Gary Tait

    Gary Tait Guest

    Simply, you can kinda use a c-clamp, and count the turns the handle
    makes. To be accurate, you'd need a fine thread, and a plantary device
    to make turns on the handle turn the screw slower. You might also want
    to have some sort of pressure sensor on the fixed end, to know you
    have turned the handle enough.
     
  3. Garrett Mace

    Garrett Mace Guest


    I have also seen some digital micrometers which have a solid core that
    slides through a tube. An ultrasonic transducer is positioned at the end of
    the tube, and by analyzing the changing resonance of the cavity, the
    position of the plunger can be determined. This may work by simply detecting
    how the sound waves cancel out or reinforce each other as they bounce within
    the chamber. I'm not sure how much typical barometric pressure variations
    affect the measurement.
     
  4. Jack Smith

    Jack Smith Guest

    Maybe something closer to a digital caliper would be easier. There are
    several approaches, but one design uses a capacitive sensor. It's not
    difficult to read capacitance to 0.1% accuracy with a PIC and show a
    computed distance value on a LCD display.

    Commercial digital micrometers use a precision ground 40TPI thread and
    a interrupter to count fractional turns of the leadscrew. If you want
    0.001" accuracy, you need at least 25 interruptions/revolution. A good
    digital mike will read 0.0001 these days.

    Whether you do a micrometer or caliper, you are going to have to deal
    with precision machining. Doing a micrometer also requires dealing
    with precision threads and backlash.

    You might also post your question on rec.crafts.metalworking. There
    are more than a few folks there that have disassembled their digital
    mikes and calipers and reassembled them.

    Jack
     
  5. Ben Nguyen

    Ben Nguyen Guest

    I was looking at my computer mouse, and that seems to do something similar.
    What if I use the rolling mechanism that the ball turns and its circuit
    board to make a digital caliper?

    Does anyone know how that circuit works or how I could make something
    similar?

    Thanks!
     
  6. Ben Bradley

    Ben Bradley Guest

    Making something that works the same way a current digital
    micrometer works might be too challenging. I suggest an LVDT
    (including circuitry) and a DMM. I've made one like the one used here:

    http://www.keckec.com/seismo/

    except I didn't think it worked very well, so (inspired from an
    online article about coils-only LVDT's on the LIGO project,
    http://www.ligo.caltech.edu/docs/P/P010035-00.pdf) I wound a
    small-diameter coil that moves inside the other two, and and use that
    as the primary instead of the fixed primary coil.
    Part of the fun is that everything (except the digital multimeter,
    which is an off-the-shelf product) is analog. :)
     
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