Cheap DIY DRO scale, do they work?

[MachineTom]

What kind of resolution do you get from this setup. You need something in the better than .0005" even if you keep the scaling at .001" on the readout. Can you modify the readings to correct errors in the gaging.

I found nothing in the articles that addressed the accuracy, repeatability or resolution.

Those would be the first questions to answer.

 

[ycroosh]

I have been playing with EAGLE, does this seem right, I am a bit in doubt about the supply at the LM339 at pin 1 - 2 - 13 and 14, it have been a couple of years since my last play with EAGLE, so I am a bit rusty.




Holt

Holt,
This looks correct. The only little thing: you can skip R7 and R8. You can tie the two virtual grounds to the first comparator.

Thank you
Yuriy

 

[ycroosh]

What kind of resolution do you get from this setup. You need something in the better than .0005" even if you keep the scaling at .001" on the readout. Can you modify the readings to correct errors in the gaging.

I found nothing in the articles that addressed the accuracy, repeatability or resolution.

Those would be the first questions to answer.

MachineTom,
Would this work: http://www.yuriystoys.com/2013/12/selecting-scales-for-dro.html

Spoiler alert, though: Chinese capacitive scales aren't going to be better than .0005". On the other hand, I'm SO happy to have an iGaging scale on my lathe, even though I don't trust it for more than +/-0.002" or so. It still saves me a ton of time.

Thank you
Yuriy

 

[Holt]

You mean like this?




Holt

 

[ycroosh]

You mean like this?




Holt

Exactly.

Do you mind if I post your schematic on my blog?

EDIT: You probably know this already... Most 1.5V scales have the frame connected to Vcc; most of the other scales have the frames connected to the ground. Unless you isolate the cpacitive scale (and make sure chips can't short it to the lathe's body) you will probably let the "magic smoke" out of something (probably the voltage regulator on the LaunchPad)

Thank you
Yuriy

 

[Holt]

You are most welcome, but I would like to tidy it a bit up before you post it, I will mail you the result in a couple of days.


Holt

 

[ycroosh]

You are most welcome, but I would like to tidy it a bit up before you post it, I will mail you the result in a couple of days.


Holt

Sounds good. Thank you.

 

[Holt]

Well, I went for Yuriy's brilliant TouchDRO and I am using a rotary encoder for the main slide, first reason because I have it, and second reason because it is easy to use with the TouchDRO system, I was afraid it wouldn't be possible to implement into a DRO controller, but with this setup you can insert the counts (steps) per inch independently for each axis, and therefore mix whatever you might have or can get cheap. I got the encoder for main slide, a Heidenhain glass scale with interpolation box resulting in 0.5 micron steps! for the cross slide, and then I just got this old tool height measurer



One of the scales will be mounted on the compound.
Here is a video of my first test setup, the first red PCB is the MSP430 microcontroller, the next is my board (cardboard ) and then a short look at the Bluetooth sender, the interpolation box and glass scale over the rotary encoder to my 10.1" android tablet.



I will run a length of timing belt at the back of the lathe to run the rotary encoder, I think I will make a new tread in machine modifications once I get it mounted.


Holt


Oops, just forgot the link to yuriy's site with the project:
http://www.yuriystoys.com/p/android-dro.html