Understanding control boards

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12 May 2020 02:31 #167447 by jbloggz
I come from a 3d printing background, and have an MPCNC that runs off GRBL, so believe I understand arduino based systems well enough.
I am currently building a LEAD CNC, and was wanting to try LinuxCNC, but am having a hard time understanding the different control/breakout board options.
On one hand, it seems like the obvious choice would be a cheap parallel breakout board from eBay.
On the other hand, there seems to be a lot of talk about Mesa (and other similar) boards, which look like they connect via ethernet, and are so much more expensive.

I'm having trouble understanding why it would be better to choose one of those options over the other. What would be the reason for going for the expensive boards? Is there things that they can do that the cheap parallel breakout cant?

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12 May 2020 03:43 #167456 by Todd Zuercher
Yes a typical Mesa card can do alot more than a simple parallel port.

A parallel port is just simple bit banged io, and is accessed in software, and does software stepping and is limited to the speed of base-thread where it's software driver runs. It is also a rather limited number of io points (only 17 in one of 3 different arrangements 12out/5in, 4out/13in, or 8out/9in)

The Mesa cards offer the benefits of hardware step generation and encoder counting (at MHz speeds), optional digital to analog conversion, analog to digital conversion, and potentially huge quantities of digital IO.

For example a Mesa 7i92 that connects to an Ethernet port, can directly replace two parallel ports, with the advantages of hardware step generation and encoder counting.
But with some optional daughter cards from Mesa it can offer hundreds of digital io points as well, and many other things to. Plus most of those io points can be isolated and use higher voltages than noise prone TTL signal the parallel port uses. (such as the 24v commonly used for automation)

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12 May 2020 04:55 #167462 by jbloggz
Thanks for that explanation.
I don't think IO would be an issue for me. I'll only be needing the standard pins for stepper drivers etc. nothing fancy, just a standard CNC router.
Is the hardware step generation (and other speed benefits) something that a casual user would even notice? Also is the signal noise really a problem in practice?

I'd like to avoid spending more on the control board if I can help it, but if its really a noticeable difference, then I'll fork out for something better.

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12 May 2020 06:37 #167467 by bbsr_5a
for a standard CNC
you will be fine with a cheep setup kit
even 80% of the machines still run on this

and you can come easy to a 5m/min Wood cnc router

so get you the Mach3 5Axis cheep and a older PC

Download the MINT DVD or the standard as preferd on linuxcnc.org
and burn a DVD then simply start up on this DVD and see what numbers your pc got
everything below 50000 / 50K latency is fine for a good running CNC

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12 May 2020 06:50 #167471 by jbloggz
That's good to hear.
So something like this would be fine?
www.ebay.com.au/itm/5-Axis-CNC-Breakout-...REEN-AU/283809218477

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12 May 2020 13:06 #167514 by Todd Zuercher
How noticeable it may be will depend alot on your machine's configuration. High resolutions and hi speeds will obviously benefit more from the hardware step gen. But for most simple 3 axis step motor machines, yes a parallel port or two are more than good enough. I am running several wood routers with them at work. But if your IO needs are more than one port can handle, the cost advantage quickly starts to diminish. If you don't have a PC with a parallel port or need two a PCIe dual parallel port card that may or may not work with Linux costs about 2/3 the price of a dual DB-25 port from Mesa, (Finding a PCIe parallel port card that works is an adventure in it's self, most PCI ones are ok though.)

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12 May 2020 13:14 - 12 May 2020 13:14 #167515 by Todd Zuercher

jbloggz wrote: That's good to hear.
So something like this would be fine?
www.ebay.com.au/itm/5-Axis-CNC-Breakout-...REEN-AU/283809218477


I've used a few of those boards, and they seem to work OK most of the time, but I've had a little less than reliable results from the inputs pins on one of mine, and I had to add some pull ups to another one to work with an obstinate parallel port card..
Last edit: 12 May 2020 13:14 by Todd Zuercher.

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12 May 2020 14:17 #167527 by jbloggz

Todd Zuercher wrote: If you don't have a PC with a parallel port or need two a PCIe dual parallel port card that may or may not work with Linux costs about 2/3 the price of a dual DB-25 port from Mesa


I Just had a look and it turns out the old PC I was planning to use doesn't have a parallel port (I just assumed that it would have one). So perhaps the parallel route is not the best option.
Any recommendations for a (hopefully cheapish) Mesa board (or equivalent) that would work with a standard LEAD CNC? I dont need any fancy features. The only thing I'd like to be able to do is use a joypad (I have a spare PS3 controller if that works).
I'm in Australia, so I dont know if that changes/limits my options.

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12 May 2020 15:28 - 12 May 2020 15:30 #167532 by Todd Zuercher
The DB25 Mesa Cards can be used in the same places as an ordinary parallel port card. Only the configuration in Linuxcnc is a little different. There is the 5i25 (PCI) for $89(US) the 7i92 (Ethernet) for $89 or the $6i25 (PCIe) for $109. All 3 of these are pretty much the same except for how they plug into the PC. You can connect them using an ordinary parallel port breakout board or buy a nicer BOB with more features from Mesa if you need them. Then there are boards like the 7i96 ($119) which is like a 7i92 with the break out board already built in,with 5 step/dir outputs, 11 3-36v isolated inputs, 6 isolated 36v 2a outputs, a DB25 header (with 17 additional ttl io points) and a Smart Serial expansion port.

However I know shipping to Oz can be costly.

I've never tried myself, but I know I've seen post here about people using such game pads for contol pendants, I think it works.
Last edit: 12 May 2020 15:30 by Todd Zuercher.
The following user(s) said Thank You: tommylight

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12 May 2020 20:06 #167543 by jbloggz
Thanks, of those options, it seems like the 7i96 is probably the best value. I might look into getting one of those. Any recommended places to buy them?

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