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'[EE] Power over Ethernet hubs'
2006\08\16@104819 by Alan B. Pearce

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Does anyone know of any small hubs, roughly equivalent to the small 5 & 8
port ones you can buy for home use, that have the ability to supply PoE
power to peripheral units? I have a potential application that could use
cheap items that could supply such power, without going to a full rack mount
switch at considerable expense.

TIA

2006\08\16@111935 by Steven Howes

picon face
> Does anyone know of any small hubs, roughly equivalent to the small 5
& 8
> port ones you can buy for home use, that have the ability to supply
PoE
> power to peripheral units? I have a potential application that could
use
> cheap items that could supply such power, without going to a full rack
> mount
> switch at considerable expense.
>


If its only a handful of items you could try one of those power bricks
with 2 rj45 sockets on it. One goes to the switch the other goes to the
patch panel etc and it adds PoE to the cable. Saves forking out for a
new switch just for a phone or two

Steve

2006\08\16@152144 by Gerhard Fiedler

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Steven Howes wrote:

>> Does anyone know of any small hubs, roughly equivalent to the small 5 &
>> 8 port ones you can buy for home use, that have the ability to supply
>> PoE power to peripheral units? I have a potential application that
>> could use cheap items that could supply such power, without going to a
>> full rack mount switch at considerable expense.
>
> If its only a handful of items you could try one of those power bricks
> with 2 rj45 sockets on it. One goes to the switch the other goes to the
> patch panel etc and it adds PoE to the cable. Saves forking out for a
> new switch just for a phone or two

Here http://en.wikipedia.org/wiki/Power_over_Ethernet they show such a
"brick": a D-Link "PoE injector".

Gerhard

2006\08\17@075301 by Alan B. Pearce

face picon face
>If its only a handful of items you could try one of those
>power bricks with 2 rj45 sockets on it. One goes to the
>switch the other goes to the patch panel etc and it adds
>PoE to the cable. Saves forking out for a new switch just
>for a phone or two

Haven't come across those, but essentially I would expect to be powering up
to 8 devices.

My thoughts run along the following lines, to power a PIC-ENC26J80 from PoE
as a sensor, and report back to a central PC. Using PoE is an initial
thought on how to power it, but on second thoughts I am wondering if a
better way would be to use a CAN bus, and draw power from that at each
sensor.

The whole project is still vapourware thoughts at present, on how to deal
with RFID sensors, which may be the non-programmable type to get the chip
real cheap, but be able to rapidly associate the chip number with an item ID
by a database match in a PC. Hence I was considering the Ethernet to get a
fast transfer to the PC to do the lookup. The PC would then forward the
"human readable" ID with sensor ID to an appropriate place.

2006\08\17@075716 by Alan B. Pearce

face picon face
>Here en.wikipedia.org/wiki/Power_over_Ethernet
>they show such a "brick": a D-Link "PoE injector".

OK, but as I would be running several devices off a hub, I wouldn't really
want to put one of those on each line. I could see the cost escalating
rapidly.

2006\08\17@111444 by Howard Winter

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flavicon
picon face
Alan,

On Thu, 17 Aug 2006 12:57:09 +0100, Alan B. Pearce wrote:

> >Here en.wikipedia.org/wiki/Power_over_Ethernet
> >they show such a "brick": a D-Link "PoE injector".
>
> OK, but as I would be running several devices off a hub, I wouldn't really
> want to put one of those on each line. I could see the cost escalating
> rapidly.

PoE Injectors come in a number of flavours, and I saw one that had 6 sockets on it a while ago - I can't remember where, but I think it was on a Home
Automation web site.  I think you're unlikely to find a small hub/switch with PoE - it's a niche market that hasn't been addressed.

Of course, you can always do your own thing as long as you don't ride a coach and horses through the standards, or you keep it all in-house.

If you want to go the CAN route, there are PC-adaptors that will handle getting things to and from the PC without involving Ethernet.

Cheers,


Howard Winter
St.Albans, England


2006\08\17@113154 by Alan B. Pearce

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>If you want to go the CAN route, there are PC-adaptors
>that will handle getting things to and from the PC
>without involving Ethernet.

My thinking is rapidly going towards the CAN route, rather than attempting
to deal with the intricacies of IP, and I suspect it would work out quicker
and cheaper as well. The PC end would then become a CAN-PIC to USB or
serial, and then use my own CAN protocol.

2006\08\17@120649 by Howard Winter

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flavicon
picon face
Alan,

On Thu, 17 Aug 2006 16:31:41 +0100, Alan B. Pearce wrote:

>...
> My thinking is rapidly going towards the CAN route, rather than attempting
> to deal with the intricacies of IP, and I suspect it would work out quicker
> and cheaper as well.

And probably easier to debug, I would think.

> The PC end would then become a CAN-PIC to USB or
> serial, and then use my own CAN protocol.

Indeed - have you seen these people for the PC-CAN stuff:  http://www.easysync.co.uk  ?  Not cheap (£61+ for Serial-CAN) but it may get you off the
ground quicker than otherwise.

Cheers,



Howard Winter
St.Albans, England


2006\08\17@135749 by Gerhard Fiedler

picon face
Alan B. Pearce wrote:

> My thoughts run along the following lines, to power a PIC-ENC26J80 from
> PoE as a sensor, and report back to a central PC. Using PoE is an
> initial thought on how to power it, but on second thoughts I am
> wondering if a better way would be to use a CAN bus, and draw power from
> that at each sensor.

Sounds like you wouldn't need PoE per se; just using the two vacant wire
pairs of 10Base-T(X) might work (as long as you don't hook it up to a
gigabit hub).

OTOH, the usual CAN interface needs only one pair (plus ground, but that
would be implicit in the power pair), and you can add another pair for
power -- and have still only half the number of wires you'd need for PoE.
And CAN is a multidrop bus, which 10Base-T(X) isn't.

Gerhard

2006\08\17@161650 by William Chops Westfield

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On Aug 17, 2006, at 4:52 AM, Alan B. Pearce wrote:

> I would expect to be powering up to 8 devices.
>
that'd be about a 160W power supply for your switch. :-(
(about the size of a small desktop computer supply.)

(I'm using the wikipedia article that says 48V at 400mA, for
19.2W delivered, 12.95W available after calculated losses.)

BillW

2006\08\18@041843 by Alan B. Pearce

face picon face
>Indeed - have you seen these people for the PC-CAN
>stuff:  http://www.easysync.co.uk  ?  Not cheap
>(£61+ for Serial-CAN) but it may get you off the
>ground quicker than otherwise.

Hmm, interesting people. Stateside presence for the rest of the list as
well.

But using one of these would remove the fun of dealing with another PIC ;)

I see their USB-CAN unit uses an FTDI and AT-Mega chips.

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