Digital caliper modding

posted Mar 11th 2007 11:14pm by Will O'Brien
filed under: misc hacks

This particular hack is actually used in a kit design, but it’s still pretty sweet. This is a digital read out unit that’s a kit sold by shumatech. I’ve even mentioned it in passing before. The design takes in the pulses from inexpensive chinese made digital scales/calipers, and allows one stop calibration and ouput of three axis’s of measurement. Using the interface and a usb enabled pic, and you could make your own usb digital calipers… (Hmm, I might have to make some.)

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Comments [6]

tagged: digital calipers, DigitalCalipers, dro

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So… I’m not really experienced with this much (or at all really) but could someone rig this up to read a 3d form and then auto feed that to one of those diy cnc machines? To create a “copy machine” for 3d objects? Or possibly just to get a starting point for a CAD project (which you could modify from an existing 3d object for later CNCing? Or am I missing the point of these little things?

Posted at 1:37 am on Mar 12th, 2007 by sinerasis

The purpose of a digital read out is for general milling, usually non-CNC. Otherwise you have to do all kinds of book-keeping with the dials since the amount of travel the dial measures is fixed. Let’s say 500 thousands of an inch. So if I want to move 3.45″ I have to do 6 complete rotations and then adjust the dial to 450. It’s much easier to press the rel button and then move the axis one way until the screen reads 3.45″. It is also useful for calibrating CNCs, and as an additional feedback, thought the idea there is that the stepper and ballscrew can move a precise amount when told so you don’t have to go x then go back to get to y. You can see if this move was a cut why such an operation won’t be good, since that extra would be cut you didn’t want.

Posted at 2:39 am on Mar 12th, 2007 by tillin9

Those 3 LCD displays look likt eh time circuits from Doc Brown’s time machine.

Posted at 3:22 am on Mar 12th, 2007 by KC

Those would be LED’s in the readout not LCD’s.
The Shumatech is a great unit, much better than most commercial units out there.
Well supported in the DIY community.

Posted at 9:49 pm on Mar 12th, 2007 by Royalblu

Take a look at http://www.YADRO.org (Yet another DRO) – interface kit and software for an old laptop.

Steve

Posted at 9:01 am on Mar 13th, 2007 by Steve Taylor

I used these same instructions last spring when I built a MIDI slide whistle using the calipers as the slide. The problem is that the update rate is really slow, so you had to play slowly to get it to sound smooth.

One problem is obtaining appropriate connectors to fit on the caliper, you can get them here:

http://www.littlemachineshop.com/

Personally, if I were to try another project like this, I’d buy some linear quadrature encoders like the ones made by U.S. digital. Especially since you’ll get nice things like spec sheets so you don’t have to deal with figuring out that the calipers use -1.5 volts using a logic analyzer.

If your interested, my project is shown here, it’s got some details about the caliper-fpga interface circuits:

https://courses.ece.uiuc.edu/ece395/cgi-bin/view_project.pl?spring2006_11

Posted at 10:53 pm on Mar 14th, 2007 by Peter Klemperer