Power Over Ethernet (PoE)

Getting power to a device is always a big consideration. USB has helped out enormously for devices that hook up to your PC, but it isn't always the best solution.

Power Over Ethernet has been emerging for a while, and the early implementations I found a bit ugly, and not particularly easy to work with. I'm not interested in all the dirty detail that you were forced to learn, I just wanted to plug it in, pull power out, and go.

So the search resumed last week, and here are the results:

Getting some hardware

I found a company called Silvertel in Newport who do PoE modules. A quick look at their line up made me think they were at least worth having a play with. Trying to buy PoE modules singularly to play with was really difficult. None of the module vendors I found sold directly, and didn't really make it obvious how to buy them, unless you want to phone a disti. This was true of Silvertel too. I spoke to one of their distis who are based in Cambridge, and it seems like Silvertel have been trying to get their modules in all the usual electronics catalogues. They are having a hard time, and it was suggested that all the early modules were not particularly nice to work with, so they didn't sell well, so the catalogues are very wary.

The disti kindly agreed to send me a couple of samples.

The hardware

I got the following modules as samples:

• AG9405-S - 5v out, 10 watts, requires an external bridge rectifier
• AG9412-2BR - 12v out, 12 watts, has bridge rectifiers built in

As an experiment, I also ordered a fancypants RJ45 connector designed for PoE that already has the bridge rectifiers built in. That will work nicely with the 5v module.

When the samples arrived, I decided to start with the 12v part, but soon found that all the RJ45 connectors I have (which we have nice Sparkfun breakout boards for) only have chokes, they don't have transformers. Nuts. I'll start with the AG9405S then!

Wiring up the AG9405-S

As this is the part without the onboard bridge rectifier, I'll be using the Tyco 1-6605834-1, the RJ45 connector with the bridge rectifier built in.

I looked at the datasheets, and it all looked fairly straightforward. The plan of action was:

• Wire the AG9405 onto a piece of stripboard
• Glue the RJ45 connector upside down onto the breadboard, and use flying wire
• Put a SIL socket for an mbed board.

First off, look at the datasheets:

• AG9405-S Datasheet
• Tyco 1-6605835-1 RJ45 PoE Connector
  • RS Order code 615-4434

AG9405

AG9405 pin	Connection
1	Vin+ - Connect to RJ45 pin 9
2	Vin- - Connect to RJ45 pin 10
3	NC
4	NC
5	NC
6	NC
7	-Vdc - Connect to mbed GND
8	+Vdc - Connect to mbed Vin
9	Adjust - Not needed
10	NC

Tyco 1-6605834-1

1	RD+ - Connect to mbed RD+
2	RD- - Connect to mbed RD-
3	NC
4	NC
5	TD+ - Connect to mbed TD+
6	TD- - Connect to mbed TD-
7	Not populated
8	Not populated
9	Vout+ - Connect to AG9405-S Pin 1
10	Vout- - Connect to AG9405-S Pin 2

Ta daaa!

Click for a closer look!

Testing it out

You can import the attached projects into your compiler and build it to test. Dont forget to create "index.htm" file!

• HelloServoDemo

Click for a closer look!

Hurrah! It works!