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Help hook up a Vectrex controller to a PC

Discussion in 'General Electronics' started by [email protected], Dec 11, 2005.

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  1. Guest

    Okay, so I'm writing an article about how to play classic vector arcade
    games on your Vectrex. I've got it all working nice, but I'd like to
    create an interface to use the original Vectrex contoller. Here's what I

    The original controller varies the voltage on the X/Y output pins from -
    5v to +5 volts as you move the stick. The interface I'm using to the PC
    is an A-Pac from Ultimarc.

    It measures the resistance across 5k, 10k, 50k or 100k pots for its XY

    I'm pretty clueless as to how to go about translating the output from
    the Vectrex controller to a varying resistance in the range required.
    The other problem is that I won't have a -5v source, only the +5v
    present on the a-pac.

  2. Jasen Betts

    Jasen Betts Guest

    what's inside the vectrex controller, is there's nothing but a pair of
    potentiometers you can probably connect it directly to a PCs joystick

  3. Guest

    I'd like to accomplish the objective without opening the controller. You
    have to ruin the stickers to open them.

    If I use a volt meter to test the resistance on the X pin to ground, it
    goes like this as I move the stick from far left to far right: 20k ->
    10k -> 20k. Far left has the exact same resistance as far right. That
    won't work. I need to know if there is a way to convert voltage to
    resistance; whether that's against the laws of physics or just economics. ;)

  4. Tim,

    Economics I guess. You can control a servo system (motor + controller) with
    a voltage and you can drive a pot with a servomotor. Servos for hobby use
    are available. They're used in model aircraft for instance. So technically
    the problem can be solved but I bet it's not cheap.

    Can't you find out how a-pac reads out the pots? Maybe you can fake the
    a-pac once you know.

    petrus bitbyter
  5. Jasen Betts

    Jasen Betts Guest

    what about measuring from the +5 and -5 terminal?

  6. Guest

    Ah ha! Yes, that makes it more clear. What happens is this:

    When you move the stick left, resistance between -5v and X is 0k. Resistance between X and +5v is 10k.

    When you center the stick, resistance between -5v and X is 20k. Resistance between X and +5v is 20k.

    When you move the stick right, resistance between -5v and x is 10k. Resistance between X and +5v is 0k.

    This makes complete sense if it's going to vary the voltage between -5 and +5, with 0v being center.

    Now... is there a relatively simple way to convert that to instead provide a range from 0k to 20k as I move the stick from left to right, with 10k being in the center... without opening the case?

    Overview of desired conversion

    Current Behavior / Desired behavior

    Left / Left
    -5 to X = 0k A to B = 0k
    +5 to X = 10k

    Center Center
    -5 to X = 20k A to B = 10k
    +5 to X = 20k

    Right Right
    -5 to X = 10k A to B = 20k
    +5 to X = 0k

    I think it's above my skill level to figure out a simple cheap way to do it.

  7. Jasen Betts

    Jasen Betts Guest

    hmm X - +5 X - 0V x - -5

    Left 0 20K 10K
    centre 20K 0 20K
    right 10K 20K 0

    that's a puzzle in itself hmmm...

    +---------------------- X
    | |

    that would produce what you measured... hmmm no. there's a Y also

    -------+---------------------- X
    | |
    | |
    ----------------+------------- Y

    I wonder why they did ty like that...

    anyway the best way to use it looks to be as a voltage divider

    it's taxing me too.

    joystick inputs don't need to be driven by variable resistors to +5V
    anything that can cause the internal 555 chip (equivalent) to change state
    at the right time will do, you could use a variable current source. but
    to get a linear response you'd need to vary the current as the reciprocal
    of the input voltage.

    iK typ
    ? ---> >---/\/\--+-DIS
    | 10n typ

    hmm is there a way to do 1/X using op-amps?

  8. Guest

    I found the actual schematic of what's inside there.

    The pots are 10k.

    I still haven't figured out how to do it. :(

  9. Jasen Betts

    Jasen Betts Guest

    get a busted one and replace the pots.

    I made a joystick once, got two pots tied the spindles together
    at 90 degrees, attached one pot to a bracket on the base
    and the other to he stick.

    It did the job, (got me through galactix)

    there's a way - I think you'll need either exponential and log amplifiers
    stages or a pwm stage, I don't think the correct transformation can be done
    using only linear combinations.

    I think It's beyond me.

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