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'[PIC]: Get position from a DIGITAL CALIPER ?'
2001\07\29@115829 by Patrick J

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Is it possible to take a 'cheap' digital sliding caliper apart and use it as a
digital linear sensor w a '877 ? How do they work ?

I have a 80mm long movement which takes min 0.10 sec which I'd like
to measure with 0.3 mm resolution. I know there are expensive versions
avail w RS232, I dont think they can handle that fast movement though

/PJ

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2001\07\29@125102 by goflo

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Patrick J wrote:
>
> Is it possible to take a 'cheap' digital sliding caliper apart and use it as a
> digital linear sensor w a '877 ? How do they work?
> I have a 80mm long movement which takes min 0.10 sec which I'd like
> to measure with 0.3 mm resolution. I know there are expensive versions
> avail w RS232, I dont think they can handle that fast movement though

Machine tool supply firms sell milling machine quill DRO retrofits
which are functionally identical to digital calipers and have con-
venient form factors for many apps. These have a range of 150 mm.
Larger versions available.

Note that most cheap digital calipers DO NOT have outputs. All such
devices are quite slow - Reading a Mitutoyo "SPC" type device takes
about 34 ms. Resolution is .01 mm for the cheap stuff. Max speed is
1 meter/sec.

Mitutoyo SPC protocol is 3-wire, CLK, DATA, REQ.
CLK and DATA are open-collector outputs.
Pulling REQ low produces 52 clocks, DATA valid on
CLK low, each group of 4 bits represents a hex #,
lsb to msb:

d0-d3     0Fh

d4        sign digit, 0 is positive, 1 negative

d5-d10    measurement value, BCD, MSD to LSD,

d11       decimal point position in the 6-digit
         measurement value, counting right to left

d12       units, 0=mm, 1=inches

Its easy to use these things if you can live with the speed.
Faster devices are optical, referred to as "linear encoders",
"linear scales", or sometimes "glass scales". AFAIK all these
devices have quadrature outputs.

regards, Jack

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2001\07\29@152043 by Robert Rolf

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Longfellow makes a series of linear pots for servo systems.
(sorry, don't have a URL but any good 'source book' will list them).
With a suitable A/D you can have whatever resolution and sample
rate your require. They have units up to 6" in length and use a
glass base with evaporated metal coating so you get very long life.
(We used them on a muscle puller used in characterizing MD).

Also look at some of the linear optical sensors made by Koyocera
and the like. 10=100mm range, analog or digital outputs.

And the cheap no-name digital calipers I have do have an 'unoffical'
serial output. Clk & data, 38 bits, may tens of msec to clock
out the data (after all, it's battery powered so the processor
runs slowly to conserve power).

Robert

John Gardner wrote:
{Quote hidden}

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2001\07\30@071155 by Alexandre Domingos F. Souza

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>Is it possible to take a 'cheap' digital sliding caliper apart and use it as a
>digital linear sensor w a '877 ? How do they work ?
>I have a 80mm long movement which takes min 0.10 sec which I'd like
>to measure with 0.3 mm resolution. I know there are expensive versions
>avail w RS232, I dont think they can handle that fast movement though

       It's CheapeR to get an old mouse, and use one of it's axis to read the linear movement.


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Alexandre Souza
EraseMEtaitospam_OUTspamTakeThisOuTterra.com.br
http://planeta.terra.com.br/lazer/pinball/

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2001\07\30@180732 by Peter L. Peres
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Some cheap digital calipers have two pins where they output serial data.
Sometimes the pins are there but not visible (they are used in the 'more
expensive' model).

Peter

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