Re: Re: Displays round the house

["brougham Baker" <me@xxxxxxx>]

Stuart Poulton <swp@xxxxxxx> wrote:
>> I advocate the use of CAT 5 becasue so many of us have these
>> networks in place. But how will we get power to drive these units
to
>> the right spot?
>>
>> Is it fanciful to think we can power these displays over cat 5
as
>> well as control them?
>
> I'd need someone with more experience to clarify this, but
ethernet
> uses only 2 pairs, making the remaining 2 pairs available. 
I'm
> gussing required power would be under 1amp.
>
> Does anyone know what pairs Power over ethernet uses, what
voltage,
> AC/DC, and what max current is ?

I'll start with the easy one as this whole project has me so excited :)

10Mbps (10Base-T) uses 2 pairs, 100Mbps (100Base-T) uses all 4 pairs but
i
doubt we will ever need 100Mbps for these control level coms. For the
sake
of the pedants out there there was a 100mbps (100Base-TX) protocol that
used
2 pairs but that died a death.

Power over Ethernet info can be found at
http://www.hyperlinktech.com/web/what_is_poe.html
and a whole walk through
to make you own at http://www.nycwireless.net/poe/
Basically 1,2,3,6 are
used for data and 4,5,7,8 for power, 2 conductors each for positive and
negative if single ended power is needed.

Cat5e is 24AWG copper with a resistance of <95ohms per km for some and
<25
for others (no idea why, anyone?). The reason i give the resistance's
is
because i can't find any current ratings, although 0.2amp seems to stick
in
my head but that is for single conductors. Perhaps a physicist or EE
can
tell us what current it will take for the two conductors. It seems it
is
used at up to 48v DC, I don't ever want to try AC over them thanks,
well
other than the data.

Bro

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