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PC KEYBOARD WIRING SCHEMATIC

Discussion in 'Electronic Basics' started by [email protected], Dec 17, 2003.

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  1. Guest

    I am trying to wire and old 1920's typewriter to a modern PS/2
    connection, AT computer keyboard. I plan to basically remove the
    control IC from an old keyboard, and wire each keyswitch connection to
    a momentary button, which is hooked to mechanical levers in the
    typewriter. Does anyone have a wiring diagram of the internal
    keyswitches in a standard PC keyboard. I havent been able to fiond one
    online, all i keep getting is PS/2 pinouts, or the pinouts for the IC.
    thanks in advance,
    -Rich
     
  2. CFoley1064

    CFoley1064 Guest

    I am trying to wire and old 1920's typewriter to a modern PS/2
    Good morning, Rich. That's a cool idea, which should be quite a bit of work.
    $2.50 will get you free advice and a cup of coffee at Starbucks, so for what
    it's worth, a few observations....

    The one time I wanted a keyboard schematic (arc-percussive welder/high noise
    environment, wanted to do additional filtering of signals without
    optocoupling), I had to call the keyboard manufacturer's US office and ask.
    They sent one over with no problem. You might have to use the usual subterfuge
    to get them to cooperate.

    Communication between the PC and the keyboard is accomplished through a
    proprietary serial communication protocol. The original IBM PC had a dedicated
    Intel peripheral chip to accomplish this, and the AT and later keyboards use a
    dedicated microcontroller IC in the keyboard which reads the key matrix and
    then communicates the results to the PC. Since there aren't individual outputs
    for each of the keys, you can't get there directly from the keyboard. Even if
    you were to disable/remove the microcontroller and just run directly off the
    individual keyswitches, the 102 keys are read by the microcontroller in a
    matrix, so you will need to manufacture a scanner circuit to read the keyboard
    matrix and translate the signals to individual outputs. For a hobbyist
    project, this doesn't look too hopeful.

    But, there are ways to get the cool effect you're looking for. First, I would
    look at the IBM Selectrics (II and newer). They have a data port in the back,
    where you can control the typewriter with outside logic level signals. A
    friend did a PC/Selectric typewriter interface about 20 years ago, and was
    happy with the results. A standard digital I/O board such as the Measurement
    Computing CIO-DIO-48 ($119.99 USD) would be just about all you'd have to buy.
    You could put that card in an old PC, sweat out the comm I/O and timing issues
    in the programming flavor of choice, and you're good to go.

    If you _really_ want to use individual solenoids to flip the levers, you might
    want to try getting a couple of CIO-DO48-DD boards from Measurement Computing
    ($199.00 USD ea.). Each output can drive up to 500mA at 50VDC, which should be
    enough for small solenoids (you're going to need a lot of those, too, but
    that's another story). Slap those in an old PC, wire 'em up, program, and
    you're done.

    There are a lot of very difficult mechanical issues involved in getting enough
    electrical solenoids into such a small space as the underside of an old
    Underwood. The earliest electric typewriters were bulky, balky, and quickly
    junked as better ones became available. Pretty steep learning curve there.

    Summary:
    1) Very difficult to do this without some kind of computer between the keyboard
    and the typewriter.
    2) Cool effect possible with IBM Selectric II or III.

    Good luck.
    Chris
     
  3. JW

    JW Guest

    Unfortunately, what you ask for is near impossible. The keyboard x-y matrix
    will vary from one manufacturer to the next. You'll have to pick your
    keyboard, open it up and remove the PCB/controller, then ohm out your
    specific matrix.
     
  4. Eric R Snow

    Eric R Snow Guest

    Greetings Rich,
    I had a similar question and the answer was a device called the IPAC.
    This device is a keyboard emulator. What you do is wire switches to
    the device and then program each switch. This is done by plugging the
    IPAC into your computer and the keyboard into the IPAC. Then, press
    the switch you want to program and the IPAC will tell you to press
    the key you want to emulate. So it only requires you to press the key
    on the old typewriter and then press the corresponding key on your
    computer keyboard. After the IPAC is programmed the computer keyboard
    can be removed. This is the simplest solution and it is working well
    for me. I have no connection to the IPAC other than being happy with
    the device and customer service. The IPAC 4 has 56 inputs and if you
    need more they can be daisy-chained.The web address is:
    www.ultimarc.com
    I hope this helps.
    Cheers,
    Eric R Snow
     
  5. Rich,

    The keyboard interface to the PC has been defined. The inner workings of the
    keyboard is up to the manufacturer. Most of the old keyboards I opened
    contained an Intel 8048 micro with a 6MHz Xtal and some small amount of
    other electronics. Keyswitches are usually placed in some matrix. Best thing
    you can do is find an old AT-keyboard and wire the switches on your
    typewriter according to the matrix. Then take over the keyboard electronics
    as a whole.

    petrus
     
  6. In typed:
    In addition to the other caveats, the keys in some keyboards are
    capacitive, which means they are not really switches at all. They would
    be pieces of foil that just press down on top of PCB pads, but with an
    insulator in between.
     
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