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

  1. #11

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    Quote Originally Posted by Chuck(G) View Post
    Before I propose a solution, I'd like to know how the keyboard is scanned. After all, this could be a capacitive keyboard.
    The 3500 machine keypad uses microswitches which are open at rest. The 3189 uses a non-tactile type membrane switches also open at rest. I've verified each machine (as I have a 3500 in another location) and I can emulate button presses by jumpering pins together at the keypad connector leading to the circuit board with the keypad unplugged on both machines.

  2. #12

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    Again, BASIC Stamp. Just buy one of the starter kits and follow the curriculum. It comes on a prototyping board, but you can build your final circuit with just the chip.

    It's like Arduino without all the bloat. It predates Arduino.

  3. #13

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    Quote Originally Posted by KC9UDX View Post
    Again, BASIC Stamp. Just buy one of the starter kits and follow the curriculum. It comes on a prototyping board, but you can build your final circuit with just the chip.

    It's like Arduino without all the bloat. It predates Arduino.
    Yes! I'm sort of Embarrassed I hadn't head of this before. Looks perfect. Now I've just got to get familiar with coding it.

  4. #14

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    Quote Originally Posted by tblake05 View Post
    Yes! I'm sort of Embarrassed I hadn't head of this before. Looks perfect. Now I've just got to get familiar with coding it.
    It'll be super easy with their starter kits, you should have no trouble with it. It was designed for high school students (as far as I know) but has plenty of power for most hobbyist projects. It's been a few years since I had to use one, but I used them for industrial automation where simple PLCs were considered overkill. They have a version of the chip that is hardened with such uses in mind and will certainly suffice for your purpose.

  5. #15

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    Quote Originally Posted by KC9UDX View Post
    It'll be super easy with their starter kits, you should have no trouble with it. It was designed for high school students (as far as I know) but has plenty of power for most hobbyist projects. It's been a few years since I had to use one, but I used them for industrial automation where simple PLCs were considered overkill. They have a version of the chip that is hardened with such uses in mind and will certainly suffice for your purpose.
    Great! Ok, thanks! I think I'll order a starter kit and see what I can figure out on my own otherwise I'll be back with questions. Do you recommend using any sort of specific relays for the output side? I don't know the spec on the control board as far as how much current passes through the buttons... And believe it or not, (Kind of like everything now days), vending machine manufacturers don't provide much tech support beyond replacing the entire failed component. So getting a detailed schematic from the control board I'll be using will be next to impossible.

  6. #16

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    Quote Originally Posted by tblake05 View Post
    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&2


    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
    3189 machine, button "#" should read 9 & 2. It has been corrected. Thanks!
    Last edited by tblake05; October 9th, 2019 at 04:26 PM.

  7. #17

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    Quote Originally Posted by KC9UDX View Post
    .......They have a version of the chip that is hardened with such uses in mind and will certainly suffice for your purpose.
    Are you thinking of the 2px? I'm going between that or just the BASIC stamp 2

    https://www.parallax.com/sites/defau...Chart-0114.pdf

  8. #18

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    Quote Originally Posted by tblake05 View Post
    Are you thinking of the 2px? I'm going between that or just the BASIC stamp 2

    https://www.parallax.com/sites/defau...Chart-0114.pdf
    I don't think you'll need the px. The straight 2 should work just fine. Just make sure that gives you enough I/O. If not, go for the 2p40. I think the only ones I've used are the 1 and 2e.

    As far as relays, any small 5V relay should work. Measure the current draw and double that, get a relay big enough for that. Don't forget some small diodes for the coil side. But here's the thing:. You might not need any relays. If the existing system is 5V, and the switches operate on 5V, you may be able to drive the systems inputs directly from your outputs. If so, do use resistors.

  9. #19

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    If you operate an array of relays, the job is straight forward. If you wanted to do it cheaper, one would need to know which was the source and which was the observe. This isn't important for the keyboard input but can be important for the output side of the device. Also one needs to know what the levels of the signals are.
    In other words, one side is scanning while the other side is monitoring.
    Dwight

  10. #20

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    Similar to Dwight's reply:
    Before proposing and designing any kind of solution it's imperative to first understand the basic parameters such as whether you're planning on using a "naked" 3189 input keypad or just tapping into it's existing circuit.

    If you're using a "naked" keypad then you'll need to generate and detect the multiplex signals. If tapping into the existing circuit, you'll need to identify the multiplex drive lines, voltages and polarities you're dealing with.

    Unless you use twelve output relays (physical, solid-state or bilateral IC), you'll need to check or scope the 3500 circuit to determine which are the multiplex drive lines and which are the detect lines (1, 3, 5 & 7 versus 2, 4 & 6). Likewise you'll also need to check voltages and polarities.

    Until these basics are identified, it's not possible to design a simple and reliable translator to go from a 3x5 matrix to a unique 3x4 matrix with multiple clock domains.

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