Suggestion for grblShield

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  • March 29, 2011 at 10:08 am #1553
    dkirtley
    Member

    Hi, I am entertaining myself until my board arrives. This is just an idea for that that has been bouncing around in my head while I am waiting.

    I find myself wishing for provision for limit switches.

    I could see this implemented as an Arduino Mega shield to include pins for jogging controller and maybe an LCD interface.

    Something that fits in somewhere between the plain grblShield and the TinyG.

    March 30, 2011 at 7:08 am #1554
    alden
    Member

    Limit switches are supported in the edge branch of grbl (and in the patched version we’ve forked) on port B, pins 1-3 which correspond to the Arduino digital outs D9, D10, and D11. Best to read the code in the grbl config.h file for details. Note that these are just minimum limits for homing purposes. To my knowledge max limits are not supported and would need to be hacked in to the code base. I think there are only 2 free digital bits on a standard arduino (unless you want to clobber the RX or TX lines), so a Mega might be required to get all 6 bits working.

    Alden

    March 31, 2011 at 12:29 am #1555
    dkirtley
    Member

    The mega will be my target platform. Once I get my board, I am anxious to see if I can fit anything else into memory to support a few extra bells and whistles. It leaves a lot of pins available to play with. My deepest secret goal is to add SD card support for spooling and hopefully some other storage ideas I have been thinking about. That might be something that would be better suited to something with a bit more CPU power like TinyG. Will have to see. I do have a parallel port board to play with if I can’t do what I want with this platform for the next build. (Yeah, the next build when I don’t even have the materials yet for this one — sigh )

    May 5, 2011 at 5:33 pm #1556
    dkirtley
    Member

    I went with the patched version and installed on a Duemilanove. Everything works great so far. I was looking at the original source and I don’t really see yet where the code that handles any limit. Does the patch include any code for the limits or is it just a pin assignment for making them available on D9, D10, and D11?

    The homing functions seem to be just stubs anyway so it might not really be that much of an issue.

    May 7, 2011 at 4:20 pm #1557
    alden
    Member

    I’ve seen some discussion that limits have been tried in the grbl edge branch. I’m not sure. You could check that out at the grbl github.

    May 8, 2011 at 10:01 am #1558
    dkirtley
    Member

    I have been reading the code from over there but I don’t have any idea what pins are assigned to anything or what code has been added other than vague knowledge that there is some difference from the config.h and code in the original tree or it wouldn’t have needed a patch. 🙂

    The homing function listed there seems a bit bare:

    void st_go_home()
    {
    // Todo: Perform the homing cycle
    }

    May 10, 2011 at 11:47 am #1559
    alden
    Member

    Since you posted your message the source for the grblshield patched code has been put up on the grblshield github at https://github.com/synthetos/grblShield
    The lines added/changed from the grbl edge branch have been labeled as /@grblshield@/ so you can find them easily.
    The pinouts used by grblshield are the 0.6 pinouts in config.h
    As for limit switches, I have not used these, so I’m afraid you are on your own to see how grbl uses them.
    Please let me know if this gets you where you need to. — Alden

    May 10, 2011 at 6:00 pm #1560
    cameron
    Member

    Thanks alden for the info!

    May 16, 2011 at 10:17 pm #1561
    dkirtley
    Member

    Just having the three pins for limit switches should be fine for handling both ends of the movement for all three axes. Just having both ends of travel with switches that are in series, there is enough information because you know the current step direction.

    Just something to bring up with the grbl development people when back from their hiatus.

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