hvc123
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Re: Power over HDMI

Sun Jan 22, 2012 3:28 pm

Heres one for you guys,

i wonder if it is at all possible to power the RPi from the HDMI? i have read somewhere that HDMI has power going down it upto 2 watts !!!?

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Gert van Loo
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Re: Power over HDMI

Sun Jan 22, 2012 4:09 pm

This has come up again and again. The maximum current an HDMI sink can take is 50mA. An HDMI sink can not supply current.That is from the official HDMI standard.

Just for completeness sake: The Rapsberery-Pi is an HDMI source. A TV is an HDMI sink.

hvc123
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Re: Power over HDMI

Sun Jan 22, 2012 4:11 pm

OK OK just a question…. at least you didnt say use search!

ta

AlanM
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Re: Power over HDMI

Sun Jan 22, 2012 4:14 pm

There is the MHL standard which is intended to supply charging power whilst being a HDMI sink, so a TV would supply power to a device plugged into it.  Although it is associated with HDMI it isn't HDMI.

Phones like the Samsung Galaxy S2 have a MHL port on them.  At the moment if you plug it into most HDMI TVs the phone will still run on battery power, but there are a few TVs out there which have MHL compliant sockets so that the phone can run on external power.  This means playing video from the phone on the TV won't drain the battery completely.

hvc123
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Re: Power over HDMI

Sun Jan 22, 2012 4:23 pm

i gotta say that its a shame its only 50ma not 500ma as 5v @ 500ma = 2.5 watts

ViewTouch
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Re: Power over HDMI

Thu Jan 26, 2012 5:20 pm

By mid year the market is going to be seeing a wave of HDMI plug computers with MHL.  It's my hope that the Raspberry Pi will achieve a form factor of HDMI with MHL, essentially turning any TV or display into a Linux computer or an X terminal merely by being plugged into the HDMI port of any TV or display.  If Raspberry Pi doesn't do this, then I would bet real money that it will happen anyway.  I do, of course, hope that Raspberry Pi is the first HDMI MHL Linux plug computer/terminal.

When this scenario arrives then we will have reached the point in time where a PC is a tiny device you can carry in your pocket and plug into any HDMI display or TV.  FXI tech in Norway is preparing one of these, too, by the way, and I hope it's the first of many.  Linux has been quite shut out of the tablet & smartphone device market, but this is a chance for it to play in the HDMI MHL dongle market and to dominate it.  Much of whether this comes to be is, in my opinion, in the hands of the Raspberry Pi people and their 'customers'.

fordcars
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Re: Power over HDMI

Sat May 09, 2015 2:01 pm

Guys, I have managed to power RPi2 over Hdmi here; completely an accident. I use a powered (by USB) hdmi to VGA converter, but this is still nuts

W. H. Heydt
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Re: Power over HDMI

Sat May 09, 2015 7:13 pm

ViewTouch wrote:Linux has been quite shut out of the tablet & smartphone device market....
And just what do you think the OS under Android is? I'll grant you that it is hidden away pretty well... (Likewise, OS/X is unix in a clever plastic disguise.)

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rpdom
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Re: Power over HDMI

Sat May 09, 2015 7:18 pm

Why are you replying to a three year old post? The poster in question hasn't posted since then.

loadbang
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Re: Power over HDMI

Sat May 14, 2016 5:17 pm

rpdom wrote:Why are you replying to a three year old post? The poster in question hasn't posted since then.
No idea. However I'm here as I've just found the RPi will power my HDMI passthru box which also splits Toslink optical and two line level out just fine.

Didge
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Re: Power over HDMI

Sat May 21, 2016 11:26 pm

Heya guys,

Was just passing and searching online myself for the actual voltage and then the amount of watts I could extract from the HDMI port..

Anyway, today I was shopping in town, whizzed through the cables selections and seen an HDMI to micro USB cable, first though was I can hook this to my TV and my Samsung S5, after that did not work many wonders I myself even thought it would at least save me the hassle of powering my Raspberry Pi 2 B with an external PSU..

So I can first hand tell you, it does not work, sadly..

Bummer eh, would be awesome to do such a thing and save allot of hassle every now and again if you could.
But as I found out myself earlier... it's a definite... No, using the HDMI to micro USB cable I came across :(

Hope this clears matters up regardless of the voltages and wattages or anything else..

It's a sound and solid "No!" From me..

loza14
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Re: Power over HDMI

Mon Aug 21, 2017 9:28 am

guys, you know there are HDMI connectors where you can connect external 5V power.
I wonder if this thing would not fry the HDMI port of Raspberry Pi and/or of my monitor?
Did anyone try this?

jjthacker
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Re: Power over HDMI

Sun Jan 14, 2018 6:28 pm

Yes, I Have done this. I connected my Pi 3 to an HDMI to VGA connector (which needed an external 5v supply), pulled out the power supply to shut down, and the Pi continued running (which did admittedly freak me out a little).

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mahjongg
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Re: Power over HDMI

Sun Jan 14, 2018 6:45 pm

jjthacker wrote:
Sun Jan 14, 2018 6:28 pm
Yes, I Have done this. I connected my Pi 3 to an HDMI to VGA connector (which needed an external 5v supply), pulled out the power supply to shut down, and the Pi continued running (which did admittedly freak me out a little).
Thats strange as new PI's even use a specific IC (the RT9741CGV-ND) to block current going into the PI from the 50mA 5V wire used to power the EEPROM in the HDMI monitor, and to limit current flowing out. Older PI's used a simple (BAT54) Schottky diode, but that sometimes burned out, especially when using a cheap HDMI to VGA adapter that "stole" power from the EEPROM, and used much more than 50mA.
This chip allows a few hundred mA going OUT, but blocks all current flowing IN.

IBM Portable PC
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Re: Power over HDMI

Thu Jan 25, 2018 12:52 am

So what is the definitive answer?

Can a Pi 2 be powered safely from the HDMI port, the answer appears to be yes?

glenenglish
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Re: Power over HDMI

Fri Aug 31, 2018 6:23 am

everyone has been barking up the wrong tree

HDMI lends it self to powering the device common mode, just like PoE

If the data rate isn't too high, say 25fps SD, , then it probably will work with standard PoE transformers for ethernet.

do some reading on how PoE works.
you'll be good up to 50W easily done right

Glen.

Heater
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Re: Power over HDMI

Fri Aug 31, 2018 7:29 am

Do you have an example of a working PoHDMI set up? I suspect not.
Memory in C++ is a leaky abstraction .

jamesh
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Re: Power over HDMI

Fri Aug 31, 2018 8:24 am

glenenglish wrote:
Fri Aug 31, 2018 6:23 am
everyone has been barking up the wrong tree

HDMI lends it self to powering the device common mode, just like PoE

If the data rate isn't too high, say 25fps SD, , then it probably will work with standard PoE transformers for ethernet.

do some reading on how PoE works.
you'll be good up to 50W easily done right

Glen.
Talked to a HW guy who knows HDMI, this is nonsense. Please don't try this at home.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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hippy
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Re: Power over HDMI

Fri Aug 31, 2018 10:36 am

Power over HDMI is possible but it requires an injector at the TV end and a splitter at the Pi end.

This is how things normally are; the TV does not provide 5V output, it receives 5V from the Pi. 0V signals not shown -

Code: Select all

-----------.                                    .--------
          _|_                                  _|_
 Pi      |   |================================|   |   TV
         |   |================================|   |
  .--.   |   |                                |   |
--|5V|-->|___|------------------------------->|___|--> 5V
  `--'     |   Pin 18                  Pin 18   |
-----------'                                    `--------
It is entirely possible to break the cable with a splitter and injector, and reverse the provision of 5V so it comes from the TV side. This requires a PSU to inject the 5V at the TV end -

Code: Select all

                 Splitter         Injector
-----------.     .-------.        .-------.     .--------
          _|_    |_     _|        |_     _|    _|_
 Pi      |   |===| |===| |========| |===| |===|   |   TV
         |   |===| |===| |========| |===| |===|   |
  .--.   |   |   | |   | |        | |   | |   |   |
--|5V|-->|___|---|_| .-|_|<-------|_|-.-|_|-->|___|--> 5V
  `--'     |         |                |         |
-----------'         |                |  .--.   `--------
               5V <--'                `--|5V|--<
                                         `--'
There are products commercially available which allow this to be done. Those are intended to inject 5V towards the TV when a product with HDMI output does not provide the 5V signalling to the TV which a Pi does but that injector can be moved to the TV side as above. It can be proven to work by supplying 5V from the TV side and lighting a LED+R on the Pi side.

It may be possible to remove the splitter on a Pi Zero if pin 18 connects direct to 5V but we do not have full circuit diagrams so the board would have to be examined to tell. For other Pi's their pin 18 does not directly connect to 5V; a blocking diode or a regulator in later Pi's prevents the Pi being powered from pin 18.

Whether a typical HDMI cable would allow enough current to power the Pi I don't know. But the cable between injector and splitter could be replaced by some other cable which does.

It should also be possible to combine the power source with the data signalling, as is done for PoE, though whether simple PoE transformers would provide for this I don't know.

Added: It seems there are commercial products already available similar to what is described above, though in this case sourcing the supply for the HDMI TV from what would be the Pi side -

http://www.skywalker.com/Products/VANCO ... N1050.aspx
http://www.skywalker.com/Products/VANCO ... N1033.aspx

andreklein
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Re: Power over HDMI

Sun Jan 27, 2019 5:39 pm

i have it working on my pi3, it needs a quick plug and disconnect at micro usb power, but when it starts all power comes from hdmi, it runs perfectly.

DrBowls
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Re: Power over HDMI

Mon Sep 30, 2019 4:22 am

I found this forum post because i was searching powering the pi 3 over hdmi because today mine did just that. I have a raspberry pi 3 with kali on it, in my truck, attached to a 7 inch monitor because i like hacking on the go. Anyway i noticed that after i shutdown my pi and pull the power cord, my monitor shuts off to as if had pulled its power cord... Anyway, today i was driving away from a spot i had just been cracking wifis at and my pi was still shutting down. While i was driving i pulled its power cord when it was finished turning off and IT TURNED BACK ON! I was blown away! I pulled over and was looking at the power cord in my hand (detached from the pi) and looking back at the pi, on the kali login screen. I was shocked at first but then i figured that raspberry pi's could maybe just be power like that and i was just one of the last to know... Well.., thats how i got here because i was looking for instructions on how to do it again. And as ive been reading i see that it wasnt even supposed to be able to do that. Im puzzeld on how anf why it did it.

hippy
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Re: Power over HDMI

Mon Sep 30, 2019 11:37 am

DrBowls wrote:
Mon Sep 30, 2019 4:22 am
as ive been reading i see that it wasnt even supposed to be able to do that. Im puzzeld on how anf why it did it.
I was initially puzzled as well.

First the display should not be putting 5V out over HDMI and, even if it does, it would not be expected to be of sufficient current to power a Pi 3, but it is feasible some display's could

And then, if any 5V did reach the Pi 3 I was not expecting it to be able to back-feed through the RT9741CGV high-side switch and power the board's main 5V line.

However, re-reading the datasheet; "If VOUT is greater than VIN, current will flow from VOUT to VIN since the MOSFET is bidirectional when on".

If a Pi is being powered by normal means, with 5V injected on Pin 18 of its HDMI socket, it seems it can continue to draw its 5V through that even when the normal power were removed.

It seems the Pi can continue to be powered through HDMI, but not powered-up by that means.

hippy
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Re: Power over HDMI

Mon Sep 30, 2019 12:27 pm

hippy wrote:
Mon Sep 30, 2019 11:37 am
First the display should not be putting 5V out over HDMI
That appears to be as per official HDMI specification. Pin 18 on a display is 5V @ 50mA input. It is a sink only, never a source.

It is however possible that a designer of a display may abuse, subvert or add to the official specification, for example to allow a proprietary unit to connect to the display and be powered from it.

Updated : An MHL compatible HDMI sink ( TV, monitor, etc ) will act as a source for 5V on pin 18 of the HDMI connector. This allows a tablet or phone to be powered or charged while connected to the HDMI sink. It is no longer correct to say that pin 18 will be sink only on an HDMI sink device.

If they used some sort of perfect diode scheme it can operate as a sink when used with standard equipment and as a source when no power is being injected. That would avoid damaging standard equipment, and is notionally compliant with the specification when standard equipment is connected. That might even be a capability in some official specification I am not aware of.

I guess something like that is happening here.

If so, I would imagine the power is pulled on the Pi, the display sees its 5V injected disappearing and supplies 5V itself. The Pi's voltage is decaying but the MOSFET is still active, 5V is injected into it, and through it, which restores the 5V. The 'decay then recover' probably causes a reset to the SoC, which is why it starts up again.

I would hope that any sourcing in a display has over-current cut-out because devices like the RT9741 have a 'short VOUT to 0V' MOSFET fitted. Which in this mode would operate as "short external HDMI VIN to 0V".

Even if it appears to work I would advise against allowing such powering to persist as the current drawn could exceed the RT9741 and even cable ratings.
Last edited by hippy on Thu Jun 18, 2020 10:41 am, edited 1 time in total.

dann4520
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Re: Power over HDMI

Wed Oct 23, 2019 12:32 pm

hippy wrote:
Mon Sep 30, 2019 11:37 am
DrBowls wrote:
Mon Sep 30, 2019 4:22 am
as ive been reading i see that it wasnt even supposed to be able to do that. Im puzzeld on how anf why it did it.
I was initially puzzled as well.

First the display should not be putting 5V out over HDMI and, even if it does, it would not be expected to be of sufficient current to power a Pi 3, but it is feasible some display's could

And then, if any 5V did reach the Pi 3 I was not expecting it to be able to back-feed through the RT9741CGV high-side switch and power the board's main 5V line.

However, re-reading the datasheet; "If VOUT is greater than VIN, current will flow from VOUT to VIN since the MOSFET is bidirectional when on".

If a Pi is being powered by normal means, with 5V injected on Pin 18 of its HDMI socket, it seems it can continue to draw its 5V through that even when the normal power were removed.

It seems the Pi can continue to be powered through HDMI, but not powered-up by that means.
Thanks for explaining this! I use one of those powered VGA to HDMI converters and I noticed one time that upon cutting the normal power source that the Raspberry Pi did not shut off. Only after unplugging the HDMI cable did it power off. I thought "Great! I can power a Raspberry Pi using HDMI!" But, as you mentioned I could not get it to power up using HDMI power, only maintain its powered on status.

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