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Another Old Man Newbie Question — Parallax Forums

Another Old Man Newbie Question

JossJoss Posts: 32
edited 2007-03-27 21:47 in Propeller 1
When I turn on led 16 or 17 (individually) on my demo board, the led looks fine.

When I turn on (individually) leds 18-23, either the led before or after is partially lighting up.

Can anyone explain this to me?

Regards

Comments

  • cgraceycgracey Posts: 14,223
    edited 2007-03-27 21:20
    If you look at the Demo Board schematic:

    http://www.parallax.com/dl/docs/prod/prop/PropDemoDschem.pdf

    You will see that those lines not only drive LEDs, but also the VGA signals. The VGA signals are made from combining pins via resistors. Hence, pull up on one, and you inadvertently pull up on a neighbor, which winds up driving another LED. If you make all those pins outputs (23..16), this will not happen anymore, because they will all be driven either high or low.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


    Chip Gracey
    Parallax, Inc.
  • JossJoss Posts: 32
    edited 2007-03-27 21:47
    Thanks, Chip.

    I really enjoy learning these things!

    Regards
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