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Thread: Anyone good with logic gates and BJT Transistors??

  1. #1

    Default Anyone good with logic gates and BJT Transistors??

    Long story short, my wife and I own vending machines as a side income. One machine in particular would be a lot more profitable if it had a card reader. In order to add a reader, the logic board needs to be upgraded to one used in the newer model of this machine. Problem is, the keypads are not interchangeable and the new keypad has different button matrix from the old one. Therefor I've got to transpose the old keypads output to be used in place of the new one. I have figured out each ones matrix which I can post if someone thinks they can help. I'm thinking maybe use some logic gates, bjt transistors, or maybe a PLA IC may be a solution. However I am terrible at designing circuits. It is required to be robust and able to withstand years of repeated use. I can post keypad configuration if requested. Thanks for any help.

  2. #2
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    Why make it more complicated than it needs to, use an Arduino and program it to interpose the signals the way you think they should work.

    If the outputs drive something that requires moderate current, just use a bank of relays that the Arduino controls, or solid state relays if high current is required to avoid contacts welding.

  3. #3
    Join Date
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    Post what you have. It'll be a little diversion from vintage computing !

    Dave

  4. #4

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    Hello Guy, yes, I was thinking arduino but I am unsure of the reliability. It will have to go weeks at a time without requiring a reset.... If you think the arduino is capable, that's what I'll do. I've just never used one so I am a bit overwhelmed.... maybe the reason why I keep defaulting back to using semiconductors. If you could help me set up the circuit and programming, that would be great.

    Here is the matrix.... (3189 machine has to keep its original keypad which has to be integrated to work on the 3500 machine. So somehow I need to make the outputs from the 3189 translate to the outputs of the 3500 keypad so it can run its control board)

    3189 machine
    Button - pins closed (when button pressed)
    ------------------------------------------------
    1 - 11&1
    2 - 10&2
    3 - 11&2
    4 - 10&3
    5 - 11&3
    6 - 10&4
    7 - 11&4
    8 - 10&5
    9 - 11&5
    0 - 10&1
    * - 9&1
    # - 9&1


    3500 Machine
    Button - pins closed (when button pressed)
    ------------------------------------------------
    1 - 1&2
    2 - 1&4
    3 - 1&6
    4 - 3&2
    5 - 3&4
    6 - 3&6
    7 - 5&2
    8 - 5&4
    9 - 5&6
    0 - 7&4
    * - 7&2
    # - 7&6

  5. #5
    Join Date
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    Assuming that you're dealing with TTL levels and the matrix is scanned the usual way you should be able to do this with a small EPROM.

  6. #6

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    I think an Arduino is *WAY* over-complicating the problem and introduces other potential issues with reliability, power failures / resets etc.

    The basic problem is to convert various permutations of 8 inputs to 7 outputs using a sequence of simple:
    OUTa = (INa & INb) # (INc & INd) ...
    ...

    That is exactly what a PLD such as a PAL or GAL do. A simple, cheap and reliable one-chip solution.

    P.S. Is the listing for the "*" and "#" on the 3189 wrong? If not, you won't be able to produce both of them on the 3500 during translation.

  7. #7

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    I'd use BASIC Stamp.

  8. #8
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    Before I propose a solution, I'd like to know how the keyboard is scanned. After all, this could be a capacitive keyboard.

  9. #9
    Join Date
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    Quote Originally Posted by WSM View Post
    ...The basic problem is to convert various permutations of 8 inputs to 7 outputs using a sequence of simple:
    OUTa = (INa & INb) # (INc & INd) ...
    ...
    As Chuck says, we need to know how the keys are scanned; I doubt that it's as straightforward as 8 inputs to 7 outputs, more like converting 4 outputs and 3 inputs to 3 outputs and 5 inputs or vice versa (although one of the 9&1s does look like a typo).

    Nevertheless as I said, assuming TTL, switch closures and 'normal' scanning, a PAL/GAL/E(E)PROM should do the job.

  10. #10

    Default

    Quote Originally Posted by WSM View Post
    I think an Arduino is *WAY* over-complicating the problem and introduces other potential issues with reliability, power failures / resets etc.

    The basic problem is to convert various permutations of 8 inputs to 7 outputs using a sequence of simple:
    OUTa = (INa & INb) # (INc & INd) ...
    ...

    That is exactly what a PLD such as a PAL or GAL do. A simple, cheap and reliable one-chip solution.

    P.S. Is the listing for the "*" and "#" on the 3189 wrong? If not, you won't be able to produce both of them on the 3500 during translation.
    Yes, I like one chip solutions if someone could point me to one that works plus help me program/build a simple circuit......

    and yes typo, sorry, I've got the documentation at home and I'll follow up when I correct my post. Thanks

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