Think current source/sink with a good voltage compliance range,
then line length is a non-issue.

Josh Koffman wrote:

>Hi all. I have a bit of a design challenge I'm grappling with. Here's
>the deal. I have a friend who wants to make some remote indicator
>lights. In the beginning they will be controlled by switches, but I
>will be building a PIC based system in the future.
>
>We've talked about how to deal with long cable runs in the past, but
>this application is slightly unique in that the indicators are
>bi-colour LEDs. These are the ones where they are two diodes wired
>back to back. At the moment I'd like to avoid having to put in a
>remote PIC mainly due to the tight delivery schedule he needs. So how
>best to provide protection when the polarity of the line will be
>changing? Let's guess that the line length will be between 50 and 400
>feet of cat5 cable.
>
>Also, I haven't done the calculations yet for voltage drop. If anyone
>has done this in the past, tips on good voltage to use (to deal with
>line drop) would be appreciated. In the future I will be moving to a
>more solid state design and I'm thinking about using an open collector
>or similar driver with a slightly higher voltage to drive the long
>line.
>
>Thanks!
>
>Josh
>  
>

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  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.net
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