Looking for cheap linuxcnc-2.8.2 capable PC with parport - recommendations

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13 Sep 2021 07:45 #220408 by hwe
Hi all,
I am running my home-made parallelport-controlled CNC since 2010 with an very old 32-Bit PC and very old 32-bit linuxcnc versions (Ubuntu 10.04). Its for hobby purposes only.

Now it is time to get a new cheap/small/compatible PC to control my parpport-CNC machine since the old OS versions are no more compatible to internet websites and latest tool version. I would like to do some CAD/CAM on this machine as well.

I would like to get some recommendations, for what I have to look when getting a new PC to drive my CNC.
Her some of my thougths:

1. It shall be a cheap PC, preferrably with BIOS and not UEFI - my experience with UEFI is rather NIL, and I always read about booting issues with UEFI, especially when using USB-bootimages.

2. A parallelport is required - as I have read, there are PCI parallelport cards which are working fine.

3. It could also be a small industrial PC or a RASPI solution - but I also would like to do some CAD/CAM designing on the same PC. Is this efficiently doable on a industrial PC or RASPI ? 

4. What about Parallelport + RASPI - are there any working solutions ?

I just want to avoid to by an cheap 64-bit machine on ebay, and then learning that it will not work with my parport-CNC.

Thanks for any hints.

 

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13 Sep 2021 11:25 #220425 by tommylight
1.old enterprise edittion PC from Dell or HP or Fujitsu work nicely, not home or office edition.
2 Fujitsu has parallel ports even on Core i5 or i7. Some have just the mainboard header so require a backplate with DB25 connector.
3.no industrial PC, to expensive, RPI to weak.
4. Not that i am aware of.

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13 Sep 2021 12:13 #220428 by hwe
Thanks for the crisp response.
Can you give an example for "enterprise" models from HP, Dell, Fujitsu ?

From Dell can find "Optiplex" or "Precision" models - but I am not sure if this is an enterprise device.
From Lenovo "ThinkCentre" or "Elite" ?

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13 Sep 2021 12:31 #220432 by tommylight

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13 Sep 2021 13:27 #220438 by hwe
Hmm, a lot of old PCs are out there.

What if I want to use my Lenovo Laptop - is there a device available that translates USB or serial into a parallel interface which can be used with linuxcnc ?

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13 Sep 2021 14:42 #220444 by 109jb
Not sure if it would be interesting to you, but I am sort of in the same boat as you except that I don't have any desire to do CAD/CAM at the machine. I can take my laptop to the shop if I need to do that and access files through the network, or via USB Stick. For that reason I just wanted the most streamlined solution for my paraport machine. Here are my 2 finalists.

1. Raspberry Pi with a Mesa 7i92. They hook together with an ethernet cable and the 7i92 has a DB25 that will plug directly into the paraport. From there it is configuration in LinuxCNC. This is a pretty well proven solution for machine control but would not be suitable for CAD/CAM. RPi is about $100, 7i92 is $89

2. Orange Pi another single board computer like the Raspberry Pi, except this one should be able to provide the step rates I need without needing a separate card. I ordered one of these and it should arrive later this week. Cost was about $50 shipped. I plan to make a cable to connect the input/output pins of the Orange Pi directly to the parallel port breakout board on my machine. Info for this is at these links. forum.linuxcnc.org/18-computer/39037-lin...-orange-pi-allwincnc and allwincnc.github.io/

I'm going to give the Orange Pi a go with the RPi/mesa as fall back plan. I already have a RPi that is my sons that I have been playing with in simulator mode and that works rather well.

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13 Sep 2021 17:13 #220467 by tommylight
Laptops are no good for controlling machines due to all the power saving stuff crammed in, although i have 2 older ones that do work.
USB does not work with LinuxCNC for motion control, huge latency issues there.

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13 Sep 2021 17:54 - 13 Sep 2021 18:51 #220478 by hwe
Okay, since this Mesa 7i92 is connected via Ethernet, does the PC still need the real-time kernel ? I guess so ....
If not, I could just use the latest 32-Bit Debian OS on my existing PC and connect the Mesa 7i92. But most probably I need the realtime OS kernel, right ?

Edit:
I do have a 2nd Lenovo T530 laptop - I understand that there might be issues with power-saving, but before buying a new (used) desktop PC, I would give it a try T530+Mesa 7i92.

The latency test on the T530 (via Linuxcnc 2.8.2 LiveCD) gave the following numbers after ~5 minutes with glxgears, Youtube and browsing:

Servo(1ms)  Max. Int.(ns) = 1163168  Max. jitter(ns)= 163294
Base(25us)  Max. Int.(ns) =   127393  Max. jitter(ns)= 162393

I read somewhere that any value below 50000 is good, but since my speed performance is not very high, I think it might be good enough.



 
Last edit: 13 Sep 2021 18:51 by hwe.

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13 Sep 2021 18:54 #220485 by hwe
A question to tommylight - in another forum-discussion, you mentioned you are also running a laptop with high latency, and thus you had to "bump up" the CNC setting to make it work properly - what exactly did you mean with "bump up" and what ?

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13 Sep 2021 21:47 #220514 by tommylight
Not sure when or why was that but the servo period required for Mesa 7i92 can be set to twice the normal interval to avoid droping the link when used with bad latency laptops, but i would not use that for production.
You do need real time kernel, the RT-Preempt variant, not the RTAI one.
Since you have the laptop and 7i92, install, set up, leave LinuxCNC running for several days and if it does not drop the link, oh joy ! :)
For testing latency regarding ethernet Mesa boards, use:
latency-histogram --nobase --sbinsize 1000 --show
What numbers does this bring back ?

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