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Pi power

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  Pi power Tim Streater <timstreater@greenbee.net> - 2021-01-05 22:54 +0000
    Re: Pi power Andy Burns <usenet@andyburns.uk> - 2021-01-05 23:16 +0000
      Re: Pi power "Mayayana" <mayayana@invalid.nospam> - 2021-01-05 19:59 -0500
        Re: Pi power A. Dumas <alexandre@dumas.fr.invalid> - 2021-01-06 07:31 +0000
          Re: Pi power "Mayayana" <mayayana@invalid.nospam> - 2021-01-06 08:18 -0500
          Re: Pi power jornws200602@xs4all.nl (Oscar) - 2021-01-06 14:02 +0000
      Re: Pi power mjb@signal11.invalid (Mike) - 2021-01-06 09:44 +0000
        Re: Pi power Martin Gregorie <martin@mydomain.invalid> - 2021-01-06 10:31 +0000
          Re: Pi power Tim Streater <timstreater@greenbee.net> - 2021-01-06 10:44 +0000
            Re: Pi power Joe <joe@jretrading.com> - 2021-01-06 11:03 +0000
        Re: Pi power Tim Streater <timstreater@greenbee.net> - 2021-01-06 10:32 +0000
          Re: Pi power Andy Burns <usenet@andyburns.uk> - 2021-01-06 10:57 +0000
            Re: Pi power TimS <timstreater@greenbee.net> - 2021-01-06 11:44 +0000
              Re: Pi power Andy Burns <usenet@andyburns.uk> - 2021-01-06 12:10 +0000
                Re: Pi power TimS <timstreater@greenbee.net> - 2021-01-06 13:25 +0000
                  Re: Pi power Andy Burns <usenet@andyburns.uk> - 2021-01-06 14:41 +0000
                    Re: Pi power TimS <timstreater@greenbee.net> - 2021-01-06 15:17 +0000
                      Re: Pi power Martin Gregorie <martin@mydomain.invalid> - 2021-01-06 16:05 +0000
                        Re: Pi power TimS <timstreater@greenbee.net> - 2021-01-06 16:14 +0000
          Re: Pi power A. Dumas <alexandre@dumas.fr.invalid> - 2021-01-06 12:02 +0000
        Re: Pi power Andy Burns <usenet@andyburns.uk> - 2021-01-06 10:55 +0000
          Re: Pi power Chris Green <cl@isbd.net> - 2021-01-06 11:19 +0000
            Re: Pi power Axel Berger <Spam@Berger-Odenthal.De> - 2021-01-06 13:13 +0100
              Re: Pi power Ahem A Rivet's Shot <steveo@eircom.net> - 2021-01-06 12:47 +0000
                Re: Pi power Joe <joe@jretrading.com> - 2021-01-06 20:20 +0000
                  Re: Pi power druck <news@druck.org.uk> - 2021-01-06 20:43 +0000
                Re: Pi power Eli the Bearded <*@eli.users.panix.com> - 2021-01-06 23:08 +0000
                  Re: Pi power Ahem A Rivet's Shot <steveo@eircom.net> - 2021-01-07 07:40 +0000
                    Re: Pi power Axel Berger <Spam@Berger-Odenthal.De> - 2021-01-07 09:08 +0100
                      Re: Pi power John Aldridge <jpsa@cantab.net> - 2021-01-07 09:20 +0000
                    Re: Pi power The Natural Philosopher <tnp@invalid.invalid> - 2021-01-07 08:16 +0000
                    Re: Pi power druck <news@druck.org.uk> - 2021-01-07 09:53 +0000
                      Re: Pi power Martin Gregorie <martin@mydomain.invalid> - 2021-01-07 12:40 +0000
                    Re: Pi power Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2021-01-07 19:29 +0000
                    Re: Pi power David Higton <dave@davehigton.me.uk> - 2021-01-07 21:05 +0000
            Re: Pi power Ahem A Rivet's Shot <steveo@eircom.net> - 2021-01-06 12:39 +0000
              Re: Pi power Chris Green <cl@isbd.net> - 2021-01-06 17:04 +0000
                Re: Pi power Theo <theom+news@chiark.greenend.org.uk> - 2021-01-06 18:02 +0000
            Re: Pi power Theo <theom+news@chiark.greenend.org.uk> - 2021-01-06 16:41 +0000
              Re: Pi power Martin Gregorie <martin@mydomain.invalid> - 2021-01-06 17:04 +0000
                Re: Pi power druck <news@druck.org.uk> - 2021-01-06 18:50 +0000
                  Re: Pi power Martin Gregorie <martin@mydomain.invalid> - 2021-01-06 20:39 +0000
              Re: Pi power TimS <timstreater@greenbee.net> - 2021-01-06 18:58 +0000
    Re: Pi power Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2021-01-08 22:33 -0500
      Re: Pi power Anssi Saari <as@sci.fi> - 2021-01-09 12:03 +0200

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#25511 — Pi power

Having received a Pi 4B today with all the bits to make a system, I let it
install and update the OS. A bit later I shut it down, and then turned off the
Pi power supply.

The Pi carried on being powered. After dismissing the possibility of sentient
self-powered computers taking over, I discovered that the volts were coming
via the HDMI port.

Why is this? Is it normal? Is it safe? Anything special I need to do on
shutting down?

Plugging the HDMI cable back in and restoring normal power and all appears
fine But I'd like to be sure to avoid damage.

The HDMI cable is connected to one of these:

<https://www.amazon.co.uk/gp/product/B07SR1S2JL/>

which is quite handy to allow two screens on the Mac and then switch one to
the Pi.

-- 
Tim

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#25513

Tim Streater wrote:

> The Pi carried on being powered.

Unless a 4B is different to any other rPi, they never turn off, they 
just halt.

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#25516

"Andy Burns" <usenet@andyburns.uk> wrote

| Unless a 4B is different to any other rPi, they never turn off, they
| just halt.
|

? They have a power switch. I turn it on and it goes through
boot. I shut down through the GUI and it goes through
shutdown. I don't see it as different from a PC, except that
I have to turn off the power switch by hand. I suppose
if you made it from scratch you might not have a power
line switch, but it's standard with the kits. 

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#25519

Mayayana <mayayana@invalid.nospam> wrote:
> "Andy Burns" <usenet@andyburns.uk> wrote
> 
> | Unless a 4B is different to any other rPi, they never turn off, they
> | just halt.
> |
> 
> ? They have a power switch.

They don't. Like Andy said: if you do not physically disconnect the power
plug, the Pi will be halted, not powered off.

> if you made it from scratch you might not have a power
> line switch, but it's standard with the kits.

Not with my kits.

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#25541

"A. Dumas" <alexandre@dumas.fr.invalid> wrote

| > ? They have a power switch.
|
| They don't. Like Andy said: if you do not physically disconnect the power
| plug, the Pi will be halted, not powered off.
|
| > if you made it from scratch you might not have a power
| > line switch, but it's standard with the kits.
|
| Not with my kits.
|
   Interesting. I bought a kit at Microcenter. It seemed
cheaper and easier than buying separate pieces.
Included was a short length of cord with an inline switch.
So I treat it just like a computer. Since I only use it
to stream Internet/movies to a TV, there's no reason
to have it on normally. I turn it on when I want to use it.
When I'm through I go to shutdown, let the OS shut down,
then turn off the power. But I suppose if you're using it as
part of some kind of 24/7 device you'd never want to
turn it off or shut down the OS.

  I've never tried leaving the power on after shutdown,
but I know it doesn't self-boot because that HDMI input
to the TV no longer has input, even if I haven't yet
turned off the power switch. So presumably I'd have to
cycle the switch to get it to boot again. 

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#25543

In article <5ff5676c$0$304$e4fe514c@news.xs4all.nl>,
A. Dumas  <alexandre@dumas.fr.invalid> wrote:
>They don't. Like Andy said: if you do not physically disconnect the power
>plug, the Pi will be halted, not powered off.

I'm not sure about the 4, because I don't own one, but this is true for
at least all Pi's before the 4. My shiny new Pi400 does however have the
capability of a soft power off. It even has a special key-combo for it.

This is however completely irrelevant to this thread, because the OP had
his PI still being powered after physically powering the powersupply off.
-- 
[J|O|R] <- .signature.gz

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#25524

In article <i5kab6FrpbpU2@mid.individual.net>,
Andy Burns  <usenet@andyburns.uk> wrote:
>Tim Streater wrote:

>> The Pi carried on being powered.

>Unless a 4B is different to any other rPi, they never turn off, they 
>just halt.

But, from the original post, which you snipped :-

> A bit later I shut it down, **and then turned off the Pi power supply.**
> The Pi carried on being powered. 

Are you saying the Pi 4B is a stealth free-energy device? ;)
-- 
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk  |    http://www.signal11.org.uk

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#25525

On Wed, 06 Jan 2021 09:44:02 +0000, Mike wrote:

> In article <i5kab6FrpbpU2@mid.individual.net>,
> Andy Burns  <usenet@andyburns.uk> wrote:
>>Tim Streater wrote:
> 
>>> The Pi carried on being powered.
> 
>>Unless a 4B is different to any other rPi, they never turn off, they
>>just halt.
> 
> But, from the original post, which you snipped :-
> 
>> A bit later I shut it down, **and then turned off the Pi power
>> supply.**
>> The Pi carried on being powered.
> 
> Are you saying the Pi 4B is a stealth free-energy device? ;)

Its not. This just shows that, if there are common positive and ground 
rails on the Pi's PCB that are connected to ALL sockets capable of 
accepting a connection from an externally powered peripheral device, 
which AFAIK is the case for all Pi models, then a Pi will remain active 
as long as external device with a power source providing enough current 
to keep the RPi alive is connected to it.

It also means that you can destroy a Pi by connecting it to anything 
which requires more than 5v to operate and that has its positive and 
ground rails connected to the plug it uses to talk to the Pi.


-- 
--  
Martin    | martin at
Gregorie  | gregorie dot org

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#25528

On 06 Jan 2021 at 10:31:01 GMT, Martin Gregorie <martin@mydomain.invalid>
wrote:

> On Wed, 06 Jan 2021 09:44:02 +0000, Mike wrote:
> 
>>  In article <i5kab6FrpbpU2@mid.individual.net>,
>>  Andy Burns  <usenet@andyburns.uk> wrote:
>>> Tim Streater wrote:
>>  
>>>>  The Pi carried on being powered.
>>  
>>> Unless a 4B is different to any other rPi, they never turn off, they
>>> just halt.
>>  
>>  But, from the original post, which you snipped :-
>>  
>>>  A bit later I shut it down, **and then turned off the Pi power
>>>  supply.**
>>>  The Pi carried on being powered.
>>  
>>  Are you saying the Pi 4B is a stealth free-energy device? ;)
> 
> Its not. This just shows that, if there are common positive and ground 
> rails on the Pi's PCB that are connected to ALL sockets capable of 
> accepting a connection from an externally powered peripheral device, 
> which AFAIK is the case for all Pi models, then a Pi will remain active 
> as long as external device with a power source providing enough current 
> to keep the RPi alive is connected to it.
> 
> It also means that you can destroy a Pi by connecting it to anything 
> which requires more than 5v to operate and that has its positive and 
> ground rails connected to the plug it uses to talk to the Pi.

OK. So what device is providing the power to the HDMI cables, and why? In my
setup I have a Dell display connected via its DVI (?) socket and an adapter to
a small HDMI switcher that can route the display either to my Mac Mini or to
the Pi.

I did notice that, after disconnecting the HDMI from the Pi, and reconnecting
it (all this with the Pi's power adapter unplugged from the mains), the Pi did
not power up again. So whatever is on  teh HDMI is not a strong power source.

-- 
Tim

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#25531

On 6 Jan 2021 10:44:48 GMT
Tim Streater <timstreater@greenbee.net> wrote:


> 
> OK. So what device is providing the power to the HDMI cables, and
> why? In my setup I have a Dell display connected via its DVI (?)
> socket and an adapter to a small HDMI switcher that can route the
> display either to my Mac Mini or to the Pi.
> 
> I did notice that, after disconnecting the HDMI from the Pi, and
> reconnecting it (all this with the Pi's power adapter unplugged from
> the mains), the Pi did not power up again. So whatever is on  teh
> HDMI is not a strong power source.
> 

HDMI is Smart, God help us. You cannot generally power up an HDMI
source, then connect it to an HDMI sink, because the source will not
generally supply signals to an open cable. It wants to see something
alive on the other end before it will power up its output drivers. It's
all about energy saving.

Sadly, some HDMI sinks do the same. I found that my laptop could not
supply an HDMI signal to a particular Grundig monitor, because neither
end was willing to accept that the other existed. I tried many attempts
at powering them both up with varying delays between them, but could
not find a window in which both could see the other at the same time.
Both devices worked correctly with other HDMI devices.

The same will be true of HDMI 5 Volts. Not all devices do it at all,
and those which do will generally want to see something already
connected to the cable before they turn it on. Some cables do not have
the 5V line. There are several HDMI standards, and many cheap cables.
Only the most recent, for example, have an Ethernet connection.

-- 
Joe

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#25526

On 06 Jan 2021 at 09:44:02 GMT, Mike <Mike> wrote:

> In article <i5kab6FrpbpU2@mid.individual.net>,
> Andy Burns  <usenet@andyburns.uk> wrote:
>> Tim Streater wrote:
> 
>>>  The Pi carried on being powered.
> 
>> Unless a 4B is different to any other rPi, they never turn off, they 
>> just halt.
> 
> But, from the original post, which you snipped :-
> 
>>  A bit later I shut it down, **and then turned off the Pi power supply.**
>>  The Pi carried on being powered. 
> 
> Are you saying the Pi 4B is a stealth free-energy device? ;)

Ah, someone referring to my OP, instead of rabbiting on about irrelevancies.

-- 
Tim

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#25530

Tim Streater wrote:

> Mike wrote:
> 
>> Are you saying the Pi 4B is a stealth free-energy device? ;)
> 
> Ah, someone referring to my OP, instead of rabbiting on about irrelevancies.

What's relevant is that your monitor shouldn't be reverse feeding 5V to 
the Pi

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#25533

On 06 Jan 2021 at 10:57:47 GMT, Andy Burns <usenet@andyburns.uk> wrote:

> Tim Streater wrote:
> 
>>  Mike wrote:
>>  
>>>  Are you saying the Pi 4B is a stealth free-energy device? ;)
>>  
>>  Ah, someone referring to my OP, instead of rabbiting on about irrelevancies.
> 
> What's relevant is that your monitor shouldn't be reverse feeding 5V to 
> the Pi

Agreed, if that's what its doing. Could be the other Mini, I suppose. I'll
have to do some more testing.

-- 
Tim

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#25535

TimS wrote:

> Andy Burns wrote:
> 
>> What's relevant is that your monitor shouldn't be reverse feeding 5V to
>> the Pi
> 
> Agreed, if that's what its doing. Could be the other Mini, I suppose. I'll
> have to do some more testing.

Wouldn't be the biggest surprise in the world if the a cheap switch box 
just commoned all the 5V pins together (since it can act as either a 2>1 
or 1>2 device, it'll be dumb).

But a source HDMI device is expected to protect itself from an 
unexpected 5V arriving into its output, so no harm "should" occur.

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#25542

On 06 Jan 2021 at 12:10:01 GMT, Andy Burns <usenet@andyburns.uk> wrote:

> TimS wrote:
> 
>>  Andy Burns wrote:
>>  
>>>  What's relevant is that your monitor shouldn't be reverse feeding 5V to
>>>  the Pi
>>  
>>  Agreed, if that's what its doing. Could be the other Mini, I suppose. I'll
>>  have to do some more testing.
> 
> Wouldn't be the biggest surprise in the world if the a cheap switch box 
> just commoned all the 5V pins together (since it can act as either a 2>1 
> or 1>2 device, it'll be dumb).

Are these 5V signal or power? From what Joe said upthread, both ends need to
see the other. A 5V signal should suffice for that, I would have thought. No
need for the source to be offering to power the remote end.

> But a source HDMI device is expected to protect itself from an 
> unexpected 5V arriving into its output, so no harm "should" occur.

A diode would suffice.

-- 
Tim

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#25544

TimS wrote:

> Andy Burns wrote:
> 
>> Wouldn't be the biggest surprise in the world if the a cheap switch box
>> just commoned all the 5V pins together 
> 
> Are these 5V signal or power? 

Power, but only 55mA

> From what Joe said upthread, both ends need to
> see the other. A 5V signal should suffice for that, I would have thought. No
> need for the source to be offering to power the remote end.

The "seeing" is over the DDC pin

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#25547

On 06 Jan 2021 at 14:41:25 GMT, Andy Burns <usenet@andyburns.uk> wrote:

> TimS wrote:
> 
>>  Andy Burns wrote:
>>  
>>>  Wouldn't be the biggest surprise in the world if the a cheap switch box
>>>  just commoned all the 5V pins together 
>>  
>>  Are these 5V signal or power? 
> 
> Power, but only 55mA

Not enough to run a Pi, then, I imagine, but enuough to flutter the Pi's
red/green LEDs.

-- 
Tim

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#25548

On Wed, 06 Jan 2021 15:17:59 +0000, TimS wrote:

> On 06 Jan 2021 at 14:41:25 GMT, Andy Burns <usenet@andyburns.uk> wrote:
> 
>> TimS wrote:
>> 
>>>  Andy Burns wrote:
>>>  
>>>>  Wouldn't be the biggest surprise in the world if the a cheap switch
>>>>  box just commoned all the 5V pins together
>>>  
>>>  Are these 5V signal or power?
>> 
>> Power, but only 55mA
> 
> Not enough to run a Pi, then, I imagine, but enough to flutter the Pi's
> red/green LEDs.

The red LED just shows that power is on - nothing more. 

The yellow and green ones show whether the Pi is active: stop a running 
Pi with the 'sudo stop' command and all the LEDs go out apart from the 
red one, which stays on until you switch off or unplug the wall rat.

That you don't know that shows that you usually stop your Pis by powering 
them off. Not a good idea because it can corrupt the SD card - and Murphy 
says that you WILL soon or later power it off while the SD card is in the 
middle of wear balancing - this will cause unrecoverable errors.
   

-- 
--  
Martin    | martin at
Gregorie  | gregorie dot org

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#25550

On 06 Jan 2021 at 16:05:39 GMT, Martin Gregorie <martin@mydomain.invalid>
wrote:

> On Wed, 06 Jan 2021 15:17:59 +0000, TimS wrote:
> 
>>  On 06 Jan 2021 at 14:41:25 GMT, Andy Burns <usenet@andyburns.uk> wrote:
>>  
>>>  TimS wrote:
>>>  
>>>>   Andy Burns wrote:
>>>>   
>>>>>   Wouldn't be the biggest surprise in the world if the a cheap switch
>>>>>   box just commoned all the 5V pins together
>>>>   
>>>>   Are these 5V signal or power?
>>>  
>>>  Power, but only 55mA
>>  
>>  Not enough to run a Pi, then, I imagine, but enough to flutter the Pi's
>>  red/green LEDs.
> 
> The red LED just shows that power is on - nothing more. 
> 
> The yellow and green ones show whether the Pi is active: stop a running 
> Pi with the 'sudo stop' command and all the LEDs go out apart from the 
> red one, which stays on until you switch off or unplug the wall rat.

Thanks - that's useful to know.

> That you don't know that shows that you usually stop your Pis by powering 
> them off.

No "usually" about it. This is my first Pi and it was unboxed approx 24 hrs
ago.

> Not a good idea because it can corrupt the SD card - and Murphy 
> says that you WILL soon or later power it off while the SD card is in the 
> middle of wear balancing - this will cause unrecoverable errors.

Roger that, Houston.

-- 
Tim

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#25534

Tim Streater <timstreater@greenbee.net> wrote:
> Ah, someone referring to my OP, instead of rabbiting on about irrelevancies.

Wow, you sound delightful.

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