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max. length of interface cable using guibot software (for stamp 2 ) — Parallax Forums

max. length of interface cable using guibot software (for stamp 2 )

ArchiverArchiver Posts: 46,084
edited 2004-07-11 16:28 in General Discussion
Hi,

I would like to build an interface cable.
I have some interface cables (about 7 feet
each one) , is it possible to add or join
these interface cables and use one
long interface cable ( for example 79 feet) ?

Thanks, Joe



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Comments

  • ArchiverArchiver Posts: 46,084
    edited 2004-07-11 06:55
    79 feet is rather long, but I have personally run RS 232 signals that far. I believe the IEEE spec is 25 feet.

    joe terk <joeterk1@y...> wrote:Hi,

    I would like to build an interface cable.
    I have some interface cables (about 7 feet
    each one) , is it possible to add or join
    these interface cables and use one
    long interface cable ( for example 79 feet) ?

    Thanks, Joe



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  • ArchiverArchiver Posts: 46,084
    edited 2004-07-11 16:28
    I've run 9600 baud RS-232 about 250 feet by using low-capacitance cable and
    good RS-232 driver chips. I also used twisted-pair cable and terminated each
    "low" wire to the common ground, even though RS-232 is unbalanced. But your
    wire insulation needs to be pretty thick so as to increase the distance
    between the wires limit the capacitance effect which can round-off the
    square waves. Also, this much capacitance in a long cable can store extra
    electrons which needs to go somewhere and can cause ringing of the square
    waves on the cable. If you have a scope you can actually see a long cable
    ring like a bell with each signal transition. That's why we also added
    snubber resistors to terminate the far end of the signal. I think we used
    4.7k resistors, but perhaps it was a bit lower in value like 2.7k. We use
    680 ohm for balanced audio, but I don't think the RS-232 chips will drive a
    600 ohm load, but if they do then 600 would be better. Sorry, but my brain
    deletes any information more than 20 years old unless I do refresh, and this
    was in the early 80's for computer terminals mounted throughout big offices.
    Think of termination resistors as shock absorbers for your car to keep it
    from bouncing after you go over a bump.

    I don't think the Stamp makes "real spec" RS-232 which implies plus and
    minus 12 volts or so. But adding a couple of inexpensive driver chips will
    get you some serious current drive ability to help overcome the capacitance
    mentioned above. That along with the proper shielded cable to keep RFI and
    inductively coupled garbage out of the cable should allow you to get some
    real length.

    Finally, remember if you're stringing cable through a ceiling, to keep it
    away from fluorescent light ballasts which make a lots of noise and flux,
    and if it's a plenum ceiling to use fire-code rated cable with Teflon or
    non-PVC insulation. Regular PVC (Poly Vinyl Chloride) insulation breaks down
    into chlorine gas in the event of a fire, and if the ceiling is also your
    return air-duct (plenum... get it???), you could kill everyone in the
    building, or at least the firefighters.... definitely a bad thing (and a
    liability issue, per another post).

    Mike Sokol
    mike@f...


    Fits & Starts Productions, LLC
    The Leader in Recording & Sound Seminars
    "Furthering Technology & EducationT"
    www.fitsandstarts.com
    Original Message
    From: "Philip Gamlbin" <gremlin9367@y...>
    To: <basicstamps@yahoogroups.com>
    Sent: Sunday, July 11, 2004 1:55 AM
    Subject: Re: [noparse][[/noparse]basicstamps] max. length of interface cable using guibot
    software (for stamp 2 )


    > 79 feet is rather long, but I have personally run RS 232 signals that far.
    I believe the IEEE spec is 25 feet.
    >
    > joe terk <joeterk1@y...> wrote:Hi,
    >
    > I would like to build an interface cable.
    > I have some interface cables (about 7 feet
    > each one) , is it possible to add or join
    > these interface cables and use one
    > long interface cable ( for example 79 feet) ?
    >
    > Thanks, Joe
    >
    >
    >
    > __________________________________
    > Do you Yahoo!?
    > Yahoo! Mail - 50x more storage than other providers!
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    >
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    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
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    >
    >
    >
    >
    >
    >
    >
    >
    >
    > Do you Yahoo!?
    > New and Improved Yahoo! Mail - 100MB free storage!
    >
    > [noparse][[/noparse]Non-text portions of this message have been removed]
    >
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
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    >
    >
    >
    >
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