Bruny
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Re: POE support on Rpi 3

Sat Mar 21, 2015 1:00 pm

DougieLawson wrote:You now need a voltage regulator / SMPS that can handle 7V0 to 30V0 and has to drop that to 3V3. That is going to take more PCB real estate and is going to cost a lot more for something that 99.9% of ALL users do NOT want and do NOT need.

I'd prefer my Raspberry Pis complete with regular power adapter to cost £35/€35/$35 or less. I don't want to pay for fancy hardware additions that I'm never going to use.
why not focus on official Ethernet module(with and without PoE) for next A+ models with internal USB? :pinoir:
bulky?

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Re: POE support on Rpi 3

Sat Mar 21, 2015 4:27 pm

plugwash wrote:You can get POE capable magjacks with suitable transformers (the cores need to be beefier than for regular ethernet transformers to avoid saturation) and diodes inside. Not sure what the cost differential is.
I'm interested, do you have a datasheet? Ideally the DC should never flow through the transformers, it should be DC blocked.
I imagine that the pins with 75Ohm termination resistors must be brought out, so that the resistors can be added with jumpers, or removed when using POE. Probably also the resistors in the node between the center windings of the resistor, DC can be blocked there with caps that can withstand say 100V DC, but the signals must be brought out as well if you want to use them for POE.

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Re: POE support on Rpi 3

Sat Mar 21, 2015 4:40 pm

Bruny wrote:why not focus on official Ethernet module(with and without PoE) for next A+ models with internal USB?
Yabbut...the A+ doesn't have an Ethernet connection, and to add one would require adding a LAN chip...which would turn it into a form of the B series, so what would be the point?

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Re: POE support on Rpi 3

Sat Mar 21, 2015 4:48 pm

W. H. Heydt wrote:Yabbut...the A+ doesn't have an Ethernet connection, and to add one would require adding a LAN chip...which would turn it into a form of the B series, so what would be the point?
I added this to my A+ and it now has faster ethernet than either my B+ or Pi-2 :lol:

Image
http://www.amazon.co.uk/gp/product/B00KGVP71U
Last edited by mikerr on Sat Mar 21, 2015 5:07 pm, edited 1 time in total.
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Re: POE support on Rpi 3

Sat Mar 21, 2015 5:06 pm

Same add-on(network module with or without PoE) would be second eth interface when connected to new internal USB header(also used for power) on model 3.
Maybe the solution is in Pasadena which would be placed in isolated lower deck of special case :?:

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Re: POE support on Rpi 3

Sat Mar 21, 2015 10:50 pm

DougieLawson wrote: You now need a voltage regulator / SMPS that can handle 7V0 to 30V0 and has to drop that to 3V3. That is going to take more PCB real estate and is going to cost a lot more for something that 99.9% of ALL users do NOT want and do NOT need.

I'd prefer my Raspberry Pis complete with regular power adapter to cost £35/€35/$35 or less. I don't want to pay for fancy hardware additions that I'm never going to use.
For the last time: we will feed the voltage required into the ******* pins! Be it 5v or 3.3v...
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Re: POE support on Rpi 3

Sat Mar 21, 2015 10:58 pm

its impossible to feed 5V over long cables without getting an unacceptable drop, any drop over 0.25V is unacceptable.
So in any case you need something to get a stable 5V +- 5%, feeding 6V and using an 6V to 5V 1A LDO (in a TO 220 package) may be the easiest solution.

also, please keep a civil tongue!

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Re: POE support on Rpi 3

Sat Mar 21, 2015 11:03 pm

yes but its the third time i say low voltage over short cable!
mahjongg wrote: As the schematic of the magnetics ports shows they have 75 Ohm termination resistors inside that make it impossible to put any kind of DC voltage on the pins you want to use for POE, and all the connectors with magnetics I have ever seen have them, also the signal are not wired out of the port, so even if you could connect 5V to them, that 5V isn't wired out.

so whatever way I see it you need to split these wires from coming into the PI's port.
And this is irrelevant, the point is if we get two leads on the ethernet port that can power the pi we can build something that powers 50-1000-100000 pis cheaper.
Last edited by bullen on Sat Mar 21, 2015 11:05 pm, edited 1 time in total.
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Re: POE support on Rpi 3

Sat Mar 21, 2015 11:04 pm

bullen wrote:
DougieLawson wrote: You now need a voltage regulator / SMPS that can handle 7V0 to 30V0 and has to drop that to 3V3. That is going to take more PCB real estate and is going to cost a lot more for something that 99.9% of ALL users do NOT want and do NOT need.

I'd prefer my Raspberry Pis complete with regular power adapter to cost £35/€35/$35 or less. I don't want to pay for fancy hardware additions that I'm never going to use.
For the last time: we will feed the voltage required into the ******* pins! Be it 5v or 3.3v...
But that DOES NOT WORK when Joe Random or Jane Random buys his/her device (with your flavour of PoE) and plugs it into a regular STANDARDS BASED PoE injector. BANG! ONE MORE VERY DEAD DEVICE. You can't avoid that happening because the Randoms aren't going to know that you've re-written the standards, they don't care.

You may hate standards, but they're there for a purpose. Software standards are breakable because software isn't usually mision critical (except in specialist applications like air flight), hardware standards aren't breakable - because they're usually there to prevent something from getting damaged beyond repair.
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Re: POE support on Rpi 3

Sat Mar 21, 2015 11:06 pm

I don't care about standards and people that buy regular PoE for non PoE devices.

I care about being able to build a switch that powers and connects 50 pis with ethernet cables only.

To end this particular debate my flavour of PoE is not called PoE, lets call it "two pins on the ethernet plug can take the required voltage" standard.

I'm just trying to reach an informed "out-of-the-box" decision whether it's possible, not because of standards or rules or conventions, but if it's physically possible to squeeze this feature in without damaging the regular users (=not the people buying PoE for non PoE devices)
Last edited by bullen on Sat Mar 21, 2015 11:21 pm, edited 2 times in total.
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Re: POE support on Rpi 3

Sat Mar 21, 2015 11:12 pm

bullen wrote:yes but its the third time i say low voltage over short cable!
mahjongg wrote: As the schematic of the magnetics ports shows they have 75 Ohm termination resistors inside that make it impossible to put any kind of DC voltage on the pins you want to use for POE, and all the connectors with magnetics I have ever seen have them, also the signal are not wired out of the port, so even if you could connect 5V to them, that 5V isn't wired out.

so whatever way I see it you need to split these wires from coming into the PI's port.
And this is irrelevant, the point is if we get two leads on the ethernet port that can power the pi we can build something that powers 50-1000-100000 pis cheaper.
If you try to power 50 PI's from a single source, chances are that the cables will become too long already, let alone 100000 PI's, but I get your drift, however you ignore cable losses at your own peril.
so whatever way I see it you need to split these wires from coming into the PI's port
Yes, you need to split the pin 4,5 and 7,8 wires out before they go into the PI's magjack!

this typical magjack schematic might make it clear why this is needed.
Image

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Re: POE support on Rpi 3

Sat Mar 21, 2015 11:16 pm

I use 50 cm ethernet cables, no problem.

So I guess that splitting would have to be custom, there are no ethernet jacks that provide the 4, 5, 7, 8 leads bare to the pcb?

Also, to put a nail in the OP coffin, RPi 3 will certainly have USB type-C for power and ethernet? Is it bidirectional, so you can both feed and draw power, data, etc over the same plug at the same time?! Must be right since the Apple laptop only has on port...
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Re: POE support on Rpi 3

Sun Mar 22, 2015 10:49 am

The Foundation will never produce a non-standard setup for PoE. That would be insane, even if it were possible. I doubt they will even produce a standard PoE device - simply too expensive for a limited market when you can buy adapters to do the job for you.
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Re: POE support on Rpi 3

Sun Mar 22, 2015 11:47 am

DougieLawson wrote:But that DOES NOT WORK when Joe Random or Jane Random buys his/her device (with your flavour of PoE) and plugs it into a regular STANDARDS BASED PoE injector. BANG! ONE MORE VERY DEAD DEVICE. You can't avoid that happening because the Randoms aren't going to know that you've re-written the standards, they don't care.
PSE should apply voltage after signature?
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PoE: 8-30V DC on Ether1 (Non 802.3af)

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Re: POE support on Rpi 3

Tue Mar 24, 2015 4:59 pm

jamesh wrote:The Foundation will never produce a non-standard setup for PoE. That would be insane, even if it were possible. I doubt they will even produce a standard PoE device - simply too expensive for a limited market when you can buy adapters to do the job for you.
Yeah, I have given up. This is my new path:

Image

And GPIO leads... what would the best solution for many many many GPIO leads be?
Last edited by bullen on Thu Mar 26, 2015 1:14 am, edited 1 time in total.
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Re: POE support on Rpi 3

Tue Mar 24, 2015 5:40 pm

at leasy they should provide 2.5MM PIN HEADER to easily connect DC jack board(without bypassing polyfuse - MOLEX to Micro USB: Does it exist)?
4.5-40V To 5V 2A USB Charger DC Step-down


It is wrong assumption that Pi will always be near quality usb power supply. It is more likely that many have some 12V supply...

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Re: POE support on Rpi 3

Tue Mar 24, 2015 5:47 pm

Bruny wrote:at leasy they should provide 2.5MM PIN HEADER to easily connect DC jack board(without bypassing polyfuse - MOLEX to Micro USB: Does it exist)?

It is wrong assumption that Pi will always be near quality usb power supply. It is more likely that many have some 12V supply...
Except you are completely the wrong way round. I know hundreds of people with uUSB power supplies that are good enough, and about 5 with 12v (or 5, or 8) power supplies with appropriate barrel jacks.
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Re: POE support on Rpi 3

Tue Mar 24, 2015 8:50 pm

current way is not flexible even if Pi is only 4-10m away :?
The Arduino Micro can be powered via the micro USB connection or with an external power supply. The power source is selected automatically.
The board can operate on an external supply of 6 to 20 volts.
  • An optional Power over Ethernet module can be added to the board as well. 8-)

https://www.adafruit.com/images/1200x900/435-07.jpg

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Re: POE support on Rpi 3

Wed Mar 25, 2015 5:43 am

Here, a simple lifehack for POE Image
Image

just don't mix the wires, it will work flawlessly, except you will need to have a 5v power supply on the other end, or just USB from your router if it has it.

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Re: POE support on Rpi 3

Wed Mar 25, 2015 6:18 am

depawlur wrote:just don't mix the wires, it will work flawlessly, except you will need to have a 5v power supply on the other end, or just USB from your router if it has it.
And make sure the wires aren't too long. There is a reason that real PoE runs at around 30-40V and has a regulator at the equipment end...

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Re: POE support on Rpi 3

Wed Mar 25, 2015 10:00 am

Bruny wrote:current way is not flexible even if Pi is only 4-10m away :?
The Arduino Micro can be powered via the micro USB connection or with an external power supply. The power source is selected automatically.
The board can operate on an external supply of 6 to 20 volts.
  • An optional Power over Ethernet module can be added to the board as well. 8-)

https://www.adafruit.com/images/1200x900/435-07.jpg
Let me reiterate.

Not going to happen.

No point in continuing to argue for it, or compare to other products.

There are alternatives mechanisms, use one of those.
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Re: POE support on Rpi 3

Wed Mar 25, 2015 1:42 pm

Having both fixed one company's PoE interface and then subsequently designed my own (both commercial projects - anyone used Zigbee development kit from a certain vendor may have used my designs) I can with some experience say that designing-in PoE looks simple but is full of subtleties that are there to catch the unwary.

And I wholeheartedly support James when he says there's no way the foundation should half-assedly implement something badly.

Oh, and just for fun, can anyone say why that 1000pF commoning capacitor should be rated at 2kV?

Neil

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Re: POE support on Rpi 3

Wed Mar 25, 2015 2:43 pm

Neil wrote:Oh, and just for fun, can anyone say why that 1000pF commoning capacitor should be rated at 2kV?
In case you touch the cable after petting the cat?
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Re: POE support on Rpi 3

Wed Mar 25, 2015 2:58 pm

Jednorozec wrote:
Neil wrote:Oh, and just for fun, can anyone say why that 1000pF commoning capacitor should be rated at 2kV?
In case you touch the cable after petting the cat?
Funny! But no... for that you'd use a spark gap to cope with the 5kV or so you'd generate from stroking fur. Bonus points if you use an ebonite rod. Although by the time it's travelled down the cable it would have lost some of it's fast rise time (not so much a zap, more of a thump).

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Re: POE support on Rpi 3

Wed Mar 25, 2015 5:35 pm

bullen wrote:Also, to put a nail in the OP coffin, RPi 3 will certainly have USB type-C for power and ethernet?
Wouldn't count on that. That would require 1 of 2 things.

1. Manufacture RPi with usb 3.x and deal with the associated costs, does Broadcom make a Pi'esque chip with USB 3? Say the BCM 7445 for example, does support it on chip for example(I dont know if this could even be used to build a Pi compatible device)? Are there extra license costs with usb 3.x?

2. Figure out how to use a USB 3.x connector with a USB 2.0 controller.

For the next 4-10 years the micro usb connector will stay dirt cheap, something the Foundation might find to nice a deal to pass up. The problem is everyone wants to Pi to be perfect for their wants and its not about that, its about a cheap educational product. One of my friends was torqued because web browsing on Pi2 is still sluggish and I explained that to him again.

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