Raspberry Pi PoE (Power Over Ethernet) Hat

We checked additionnal pins , with rj45 input, Strange, only 2 connect

What is the ETA on the release date of the PoE hat?

Hello

If you like you can monitor the temperature of the CPU and do on off action on some fan by the GPIO

In our production we just added a fan continuousely running, it tund out to be quite important because it will go up to 80 ° or more and we had some destruction

Thomas

Hi.

Is there any information on how he fan is controlled? Is it controlled by temperature? Or maybe by a GPIO?

Thanks

Bernhard

Thomas,

For your learning enjoyment:

100 MBPS ethernet has a TX pair and an RX pair. 100 megabits, so every 10ns a new bit on each of the lines.

1 GBPS ethernet uses al four pairs. Bidirectional (i.e. for communications in both directions at the same time!), two bits per bitperiod (4 signal levels), and at 8ns per bit. All this combines to get a 10x higher datarate. (4x from 4x more line pairs, 2x from 2 bits/period and 1.25x from the higher signalling rate). Because the signalling rate is almost the same, most "officially for 100Mbps" cables can also handle 1Gbps without trouble.

I did not know on what pairs of wires the power was transmitted, but a quick readup learns me that you get to chose. Either the (100Mbps) data pairs, or the others. You'd want the first if you have a "one cat5 can transmit two ethernet signals"  construct somewhere. The other might be slightly easier electrically. For 1Gbps both choices result in power and data sharing conductor pairs.

Hi Thomas

It's definitely sure it's this connector. But you cannot use a voltmeter directly on it without the PoE HAT : A PoE802.3af injector (a simple module, or a port from a PoE switch, whatever) doesn't deliver 48V "just like this", because you can also plug a no compliant PoE device on it, and if you have 48V on the line.... bzzzzz, ciao your device ! On a PoE compliant device, you have a PD chip which establish a kind of connection with the injector, with a very low voltage, and if the communication is approved by the injector, 48V will be injected.

So :

no HAT plugged -> no PD chip on the Raspberry side -> no voltage from the injector -> you can keep your voltmeter on your shelf

HAT plugged -> PD chip present -> 48V will be delivered -> the Pi will boot -> as it will be visible, your voltmeter can still stay on your shelf

For information, the power is delivered on secondary pairs on the ethernet cable : primary pairs 1-2, 3-6 are commonly used for data transmission up to 100Mb/s (maybe can do gigabit, but not sure). When the 2 others are used (4-5, 7-8), so 1Gb/s is available.

If you want more explanation, don't forget google is your friend There's a lot of documentation online on this subject

I think the 4 pins poe hat connector has Rx+ - Tx+ - 

should be asey to check with voltmeter

and that output power 5 V goes to GPIO connector .

Can any one comment ?

I expect it will also support the stacking headers, I have seen a few add on's where you can install a low profile socket strip or a stacking strip as needed, really until someone has this kit in their hands it will be tough to be sure

Hi Daniel,

That's good to hear. In this case, it means it could be very easy to even install the PoE module alongside the Pi, with jumper cables.

And possibly the fan can be unplugged and replaced with a bigger fan, or positioned elsewhere on an enclosure if desired.

Thanks for the info!

Eben and Roger discuss it here on our interview with them.

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Eben Upton and Roger Thornton Interview: Raspberry Pi 3 Model B+ Professional and Industrial Users of Raspberry Pi Professional and Industrial Users of Raspberry Pi Comment on Raspberry Pi PoE (Power Over Ethernet) Hat

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