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'[EE]:Can you get +5V out of a 10baseT connection?'
2001\01\25@163921 by Richard Sloan

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Well?
Lets say you connect a small box to your small ethernet 10baseT network, can I get power off any of the signals without upsetting the data?

Richard.

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2001\01\25@181257 by Chris Carr

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Well Richard the short answer is No, unless you are intend consuming
picoamps of current. A perusal of the IEEE802 will  reveal that the receiver
connected to the physical media is essentially a device with a high
impedance input.

Regards
Chris

Lets say you connect a small box to your small ethernet 10baseT network, can
I get power off any of the signals without upsetting the data?

Richard.

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2001\01\25@183136 by Olin Lathrop

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> Lets say you connect a small box to your small ethernet 10baseT network,
> can I get power off any of the signals without upsetting the data?

Short answer: NO.  Long answer has to do with transformer coupling, etc,
blah, blah, but still "no".


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Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinKILLspamspam.....embedinc.com, http://www.embedinc.com

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2001\01\25@183815 by Bill Westfield

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   Lets say you connect a small box to your small ethernet 10baseT network,
   can I get power off any of the signals without upsetting the data?

No.  However, 10baseT only uses 4 of the available 8 wires in an RJ45;
I understand that some switches and/or installations are starting to
provide power (for small internet appliances like IP phones) on some
of the otherwise unused wires.  I don't know offhand whether this is
standardized or not, though...

BillW

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2001\01\25@185707 by Matt Bennett

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Chris Carr wrote:
>
> Well Richard the short answer is No, unless you are intend consuming
> picoamps of current. A perusal of the IEEE802 will  reveal that the receiver
> connected to the physical media is essentially a device with a high
> impedance input.
>
>>Lets say you connect a small box to your small ethernet 10baseT network, can
>>I get power off any of the signals without upsetting the data?
>>
>>Richard.

Actually it is relatively low impedance- the IEEE 802.3 spec states that
the ethernet transciever must be able to drive a 100 ohm load.  When I
test ethernet, I use a 100 ohm resistor.  If the interface is IEEE
compliant, a reciever should be able to communicate over a 10 dB loss
cable- this is because there is no consistent dB/m rating for unshielded
twisted pair- this works roughly to 100m (my tests actually show that a
10dB cable (at 16MHz) is about 130 m of modern CAT5 cable).  Nominally
at the transmitter the signal should be about +/- 2.5 V.

If you are willing to tolerate a decreased distance you can communicate
over, you have some margin.  On the other hand, the interface is
transformer coupled, so you would only be able to draw power when
something is actually talking on the interface.  On a 10BASE-T signal
there should always be link test pulses on an idle line, but they are
very short and only come around at a relatively low rate.

10BASE-T does only use 4 of the 8 wires that are in the standard
ethernet cable, you *could* try to use some of the other wires in the
cable to send power, but be *very* careful, often the unused wires are
terminated at the connector (usually with a 75 ohm resistor, but
sometimes with a dead short).  Any sort of noise on the other wires can
get into the ethernet signal, so the power must be *very* clean.  People
have tried to put telephone/voice over the unused pairs, but they tend
to have very poor results.

Matt Bennett

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2001\01\26@133252 by Chris Carr

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> Chris Carr wrote:
> >
> > Well Richard the short answer is No, unless you are intend consuming
> > picoamps of current. A perusal of the IEEE802 will  reveal that the
receiver
> > connected to the physical media is essentially a device with a high
> > impedance input.
> >
> >>Lets say you connect a small box to your small ethernet 10baseT network,
can
> >>I get power off any of the signals without upsetting the data?
> >>
> >>Richard.
>
Matt Bennet Replied
> Actually it is relatively low impedance- the IEEE 802.3 spec states that
> the ethernet transciever must be able to drive a 100 ohm load.  When I
Snip

I Concur - I am incorrect, well it was late at night and for some reason I
was thinking Coax Cable not twisted pair

Chris

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