How to link existing glass scale DRO readout to LinuxCNC for cheap

I finally finished a little project I had in my mind for a long time. I have some pretty common TOAUTO glass scale DROs with readout which I always wanted to connect to my LinuxCNC machine(s) to get DRO output on my touch screen and maybe also experiment with closed loop operation.

It can be done cheaply, total cost is maybe $30 in parts total, no custom parts. In essence it's based on a RP2040-Zero and a TXS0108E level shifter. The RP2040 acts as a regular USB device which can be accessed from a custom HAL component. This is not using some serial or ethernet connection but it's a full speed USB device implementation which means I can get about 1000 readouts per second. Is it as reliable as ethernet? I would not think so, but for $30 you can't ask for much more and my ethernet ports are limited

The way the electronics work is that you splice into the existing signals on the DB9 connectors on the DRO readout. So you get to keep your existing DRO panel fully working. My current hardware setup for that is rather janky, but modifying the existing DB9 connectors will probably be easier and nicer looking. The most tricky part here is that the cable lengths need to be as short as possible and ideally shielded if you want to avoid noise affecting the signal.

More information, full code and images for this project here:

github.com/tinic/rp2040-encoder

Someone should be able to solder this up in an afternoon after ordering the parts from Amazon the day before...
 

This is very interesting, Thanks. Do you have working setup? how it behaves ?  Is that link of DRO scales actually closes the loop and creates feedback) or it is providing only readout on LinuxCNC ? 

Yes, I am actively using it. I just finished hooking it up in a closed loop system so it can do canned cycles on my lathe. So far the results look good, it works great!

I have my own ELS system for which I use it for: github.com/tinic/el-linuxcnc-electron

My hal file is here, though I doubt this will be meaningful to you since my system is rather complicated: github.com/tinic/el-linuxcnc-electron/bl...p/elle-hal/lathe.hal

I was checking your GITHUB repos - great content. I am actually working on ELS myself right now. Fitting mechanical parts first to the Atlas lathe - need to add spindle encoder and stepper tot the lead-screw.

What ELS do you use ? your own design? LinuxCNC based ?

The ELS project I listed above is my design, yes. I've talked about it before here on this forum but interest seems low. Most people go for Clough42's much simpler+cheaper approach: github.com/clough42/electronic-leadscrew

My ELS system is LinuxCNC based with a web interface frontend. I use a 7i96 board which has only one encoder, hence this rp2040 based project.

My system also has X-axis steppers, not just a Z-axis stepper. One my goals is to be able to do NPT taper threads easily since I do this often and using dies is a PITA on stainless.