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Dying Parallel port pins — Parallax Forums

Dying Parallel port pins

T ChapT Chap Posts: 4,223
edited 2007-01-26 02:09 in General Discussion
Over a few days, two pins have now died on my PC parallel port. The cable runs to a board that goes into a Propeller via 1k resistors. There are 8 pins that goes into the Prropeller and also get sent to some motor driver inputs. Furtunately I had a few extra pins to swap out and keep running, but now I have no more spares. One more blown pin means I have to find another PC or parallel port PCI card if such exists. I have been hotswapping the cable. I meter between the GND on the cable and GND of the Prop boards and depending on how you go, it is either 12 or -12 from ground to ground (obviously this is with the cable unplugged). The PC and Prop PS are on the same AC strip.

The pins simply stay high when they die. Any suggestions on how hot swapping could do this to an output? Since they are exclusive outputs pins and never inputs, would an opto be the trick to solve the problem?

Post Edited (originator) : 1/25/2007 9:07:38 PM GMT

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-01-25 22:23
    Originator,

    Do you mean Serial Port? Parallel Port pins are 5V TTL level…+12V or -12V into them could damage them. Perhaps I am misunderstanding…Also; LPT ports are not friendly for hot swapping. On older computers this could result in the computer resetting on some systems. Optical isolation almost always helps in these cases. Take care.

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    Chris Savage
    Parallax Tech Support
  • David BDavid B Posts: 592
    edited 2007-01-25 22:41
    Once I stupidly made up a project that used the exact same 25-pin D style connector as the PC parallel port accepts, and my project used one of the pins to supply 12V to something. Then one day I grabbed it by mistake, plugged it into the PC and poof - I blew a parallel port pin. So from experience, I also can say that 12v can certainly destroy the parallel outputs.

    If you really want to hot-swap, maybe you should make up a separate ground lead and use it to connect the two system grounds first, to try to get rid of that 12V difference, wherever it is coming from. That's what a lot of hot-swappeable cards do - their ground lead is extended physically so it is the first to make contact when you insert the card. Even if you were to use just a simple clip-lead jumper cable, I'll bet you'd do a lot towards preventing those pins from blowing.

    If you do jump the two system grounds together, then what voltage difference shows between the pins? You don't still see any 12v, do you?

    David
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-01-26 00:08
    Parallel port hot-swapping· skull.gif· is a no-no.
  • T ChapT Chap Posts: 4,223
    edited 2007-01-26 02:09
    Thanks for the info. If the cable is plugged in, the oututs are 0 and 5v. Maybe I'll try to tie the grounds together prior to swapping.
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