Understanding control boards
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?
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)
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.
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
jbloggz wrote: That's good to hear.
So something like this would be fine?
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..
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.
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.