usb keyboard hack?

Discussion in 'The Projects Forum' started by kutalinelucas, Nov 20, 2007.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    hi guys. I have a little project in my head but im not sure how to go about a part of it.

    i need to figure a way of making a 32 button usb (or bluetooth) keyboard. I cant hack an existing keyboard because of the size of the matrix involved, and 32 inputs into a processor seems quite excessive. The other problem is the keypresses arn't mechanic so i couldn't just design a smaller matrix.
    i'm not an electronic genius, but I'm more than willing to read up on everything if i could just get a nudge in the right direction.

    thanks
     
  2. GS3

    Senior Member

    Sep 21, 2007
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    35
    I don't quite understand what you are trying to do. Can you explain?

    The key presses aren't mechanic? huh?
     
  3. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    0
    basically there is no closing of contacts like a conventional keyboard.

    the idea is just a one handed usb keyboard. i really haven't got far with it tho.

    theres a mechanical switch on the end of each finger, going into a 5-32 line decoder which could maybe go into a 6x6 matrix(?). then on to a microprocessor.

    26 of the combinations would be for the alphebet and the other 6 for other functions such as space etc.
    so, say the thumb and forefinger was pressed simultainiously, the character 'A' would be displayed on screen. when one of the switches is released, the buffer is cleared and all is reset ready for the next combination.

    i know i have alot of issues to deal with like bounce, enable timings resets etc.., but i'd like to know if i could get away with hacking an existing keyboard and building a matrix to be compatible with its microprocessor, or would i have to go down the long asm road?
     
  4. GS3

    Senior Member

    Sep 21, 2007
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    35
    I must be missing something but those two statements seem contradictory to me.
    I don't get it. Why not send the five bits directly to the processor? You want to decode to 32 lines? why? this just makes it more complicated.
     
  5. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    0
    please remember, this is still coming out of my head, and im not an electronic genius. thats why im asking for help.

    I was hoping to use an existing keyboard processor, so i could bypass learning asm and hexi coding, custom drivers etc.. i'm not doing this to get any marks! A bluetooth processor would be fantastic and impossible for me to design at my level.

    when i said no mechanical movement i meant no buttons to close a contact on a conventional keyboard matrix, but just signals from the line decoder. The switching happens before this.
     
  6. GS3

    Senior Member

    Sep 21, 2007
    408
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    I think I begin to understand what you are trying to do. Decode 5 bits to 32 lines and connect each of those to a key on a keyboard and so use the standard keyboard driver etc.

    You need to decide when a code is valid because the five switches will close and open at different times. Unless you go very slowly, how do you know when a code is good or whether you need to wait in case another switch closes?
     
  7. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
    98
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    i'll have to think about that one.
     
  8. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    It would be interesting to see if a person with some practice could use such a system usefully but I cannot see how it could be better than a standard or modified keyboard except in very special circumstances.

    The 5 bit to 32 line decoding could easily be done with a couple of 4514 chips (4 bit to 16 line decoder). Then terminate each line with a relay or other switch (FET?) for each keyboard key.
     
  9. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
    98
    0
    just thought it would be nice if i could rip a usb-on the go keyboard and use it on my PDA. it cant be much more difficult to learn than the sign alphebet.

    Each switch will be de-bounced so i'll have a good feel for the timings, but i'm not sure of the best way of resetting the switches.
    If i manage to get around that, do you think i could just create a matrix map and use an existing processor and usb port/ bt transimtter?
     
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