rs485 or i2c without microcontroller?

Discussion in 'The Projects Forum' started by ebeowulf17, Dec 13, 2014.

  1. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    So, in our machines we've got a main power board with microcontroller, power supplies, and various i/o which is housed in a decent electronics enclosure, and then various other circuit boards in remote parts of the machine.

    One group of those boards uses rs485 communication to work with the main board, while our user interface board (20x4 lcd and 6 buttons) runs through a ribbon cable with separate wires for each pin (power, ground, 6 or so for LCD, 6 more for buttons.)

    We'd like to get away from the bulky, fragile ribbon cable and use a 4 wire system (power, ground, 2 data) like i2c or rs485 for the interface, but I'm not sure how best to approach it.

    If we could make the right changes to the main board, we'd just replace the ribbon cable connector with something smaller and update the code accordingly... but that board is complex, far beyond our ability to redesign in house, and we're several years away from being ready to pay contractors for the next big revision. We can probably handle modifying the interface board design, just not the main control board.

    As an interim fix, I was thinking of using something like the expander chip on this board on the interface side to turn i2c (better still if I could find rs485 equivalent) into the relevant i/o. What I can't figure out is a way to adapt 16 pins at the main board. It looks like these i/o expander chips always expect to communicate with a microcontroller. I'd like a pair of chips that convert 16 pins into 4 wires on one end and back from 4 wires to 16 pins again on the other end. In a perfect world, it would use rs485 so that when we do finally redesign the main board we can stick with rs485 for all communication without redesigning the interface board yet again. I can't find anything like what I'm looking for, but I was hoping maybe I'm just using the wrong search terms or something.

    Anyone know if such a thing exists, or if there's a better way to achieve a similar effect? Or is this just really a bad idea, and we should continue dealing with ribbon cable until we can redesign all electronics at once?

    Thanks in advance for your help.
     
  2. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    79
    Wow, I always think I'm doing better, and then I write so, so much. Sorry. Gotta learn to be concise.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It sounds like you have other, bigger, fish to fry and grow your business and improve your product. Therefore, I would drop this rather complicated idea and postpone until your major redesign. The only thing you might want to look at is a better, more flexible ribbon cable or, possibly a more flexible 12-wire cable.
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    If you already have RS485 in your machine, it might be fairly simple to extend the network to communicate with the interface board. Electrically simple, that is--what would make it all work would be the software, and you'd have to get into the communications routines in the code to command data in and out, and obviously that needs to happen without disturbing the existing setup. And of course, the interface board itself would need matching hardware and software. But it's an elegant way to run the internal communication.
     
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