[TriEmbed] I2C range extension

[Jim Ray]

Ethernet will give you 100m or 328 ft range. With Raspberry Pi weighing in at 0.5 W, 13 W power budget with PoE is a lot.

From: TriEmbed [mailto:triembed-bounces at triembed.org] On Behalf Of Glen Smith via TriEmbed
Sent: Friday, October 02, 2015 10:51 AM
To: Carl Nobile; Pete Soper
Cc: TriEmbed
Subject: Re: [TriEmbed] I2C range extension

If you are planning to use Official PoE, remember that while the current is limited to 300ma, this is at around 44 VDC, the spec for 'regular' PoE is around 13 Watts of available power at the field end. To operate your R-Pi or other device you need to drop that down to the right supply voltage, so a shield with a DC to DC converter would do nicely.
On the other hand, there are cheap and easy power injector cables that allow you to piggy back a DC supply of your choosing onto the Ethernet cable at the head end and then pull it back off on the field end. $6 at Adafruit for a pair: https://www.adafruit.com/products/435
and if you don't need a pretty injection molded cable, you can make your own for the cost of the barrel jacks.
Clearly, some thought needs to be put into the cable lengths, DC losses and just how much power you need, but this IS a viable option.
Glen

On Fri, Oct 2, 2015 at 9:06 AM Carl Nobile via TriEmbed <triembed at triembed.org<mailto:triembed at triembed.org>> wrote:
Pete,

I just checked, there are two specs PoE and PoE+. The first one has a maximum current of 300mA and the second one has a max of 600mA. Obviously both are too low. Too bad, this was a good idea.

~Carl


On Fri, Oct 2, 2015 at 8:36 AM, Pete Soper via TriEmbed <triembed at triembed.org<mailto:triembed at triembed.org>> wrote:
WIthout a switching converter on the other end the wrong order of magnitude of current is available:

  https://en.wikipedia.org/wiki/Power_over_Ethernet#Power_capacity_limits
On 10/02/2015 07:02 AM, Jim Ray via TriEmbed wrote:
Has anyone modified Raspberry Pi to use PoE for power? Using standard Ethernet to drive a communications sub system based on another Raspberry Pi that has the requisite i/o and processor makes a lot of sense to me.


-Pete

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