Author Topic: Anyone built an SPC interface for a caliper or dial gauge?  (Read 2177 times)

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5974
  • Country: gb
  • East Sussex, UK
Anyone built an SPC interface for a caliper or dial gauge?
« on: February 21, 2015, 02:54:06 PM »
Cricking my neck reading DTI's upside down whilst adjusting my Traub tool turret it occurred to me that I have a perfectly good Mitutoyo  543-682 electronic DTI with a socket for remote reading.

Anyone built a remote interface / display for the Mitutoyo SPC interface ?
Andrew Mawson
East Sussex

Offline micktoon

  • Hero Member
  • *****
  • Posts: 797
  • Country: gb
Re: Anyone built an SPC interface for a caliper or dial gauge?
« Reply #1 on: February 21, 2015, 05:11:57 PM »
Sorry Andrew not me but only the other day I would have liked to be abled to have flipped the display the other way up, so I expect we will not be the only two. so I would make a few  :thumbup: :drool:

  Cheers Mick

Online chipenter

  • Hero Member
  • *****
  • Posts: 763
  • Country: gb
Re: Anyone built an SPC interface for a caliper or dial gauge?
« Reply #2 on: February 22, 2015, 04:35:11 AM »
I wonder iff it's a standard data port then one of these may work http://www.arceurotrade.co.uk/Catalogue/Measurement/Standard-Digital-Readouts .
Jeff

Offline DMIOM

  • Hero Member
  • *****
  • Posts: 682
  • Country: gb
  • Isle of Man
Re: Anyone built an SPC interface for a caliper or dial gauge?
« Reply #3 on: February 22, 2015, 05:38:24 AM »
I wonder iff it's a standard data port then one of these may work http://www.arceurotrade.co.uk/Catalogue/Measurement/Standard-Digital-Readouts .

Unfortunately I don't think so - I think those work with what the Schumatech & others refer to as the "Chinese Protocol".

I did a basic PIC-based interface many years ago, so following is from memory:

Four wires (Ready, Request, Clock & Data) + ground. Ready is just an output, the other three active lines are, IIRC, open-collector so can be used bi-directionally.

Ready is usually asserted on an ordinary measuring device, so you may not need to check it.

The simplest mode is where you just briefly pull REQ low and the device then blasts back the SPC bit string of thirteen BCD nibbles/digits. The data line values were read on the (falling?) edge of the clock line from the device.

The 13 nibbles/digits consisted of a three-digit start header 0xFFF, then the digits displayed on the device, then one digit containing the position in the string of the decimal point and then a final digit where 0/1 was used to indicate mm/inch (other values for metres etc.).

There is a 0/1 digit somewhere in there to indicate +/- but I can't immediately recall where that came in the sequence. Also there's a digit to indicate the type of reading - it is 0xFH for a normal reading, but there are other possibilities with devices that implement the statistical part of SPC (min, max, average, SD etc.).

As I understood it then, any devices which had a physical 'output' button (or a button built in to the lead, or even a footswitch) all just pulled that REQ line low.

The protocol is bi-directional - there are options to send limits, calibration factors etc. back to the device but I've never used them.

One issue I seem to recall is that if the operator set a "user zero" it made no change to the output - the output was always absolute.

If you want, I'll have a hunt around my old dev machine and see if I can find a detailed datasheet or my C code.

Dave

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5974
  • Country: gb
  • East Sussex, UK
Re: Anyone built an SPC interface for a caliper or dial gauge?
« Reply #4 on: February 22, 2015, 06:35:19 AM »
I thought that this is probably a good use for an Arduino with a 'display shield', and with arduinos someone has usually trodden the path before you!

Sure enough I came across a fellow who after a struggle had got a working system.

It was about this time I remembered I had a Mahr Feinpruf transducer based measuring gizmo, so in this instance my immediate need vanished  :clap:

(Details in my CNC lathe thread)

Still think given time it would be a useful exercise
Andrew Mawson
East Sussex