feelslikeautumn
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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 11:57 am

Imperf3kt wrote:
Tue Jun 12, 2018 10:47 pm
Perhaps the next Pi should include pads we can solder to so as to completely avoid the micro USB port, while still retaining the polyfuse protection.
+1

Or some sort of header. The micro USB port is problematic even with an official power supply (for example I've had undervoltage warnings with no peripherals connected). It's crazy talk to deny there are issues with the choice of micro USB.

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mahjongg
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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 12:17 pm

hippy wrote:
Tue Jun 12, 2018 3:56 pm

I disagree about barrel connectors not being appropriate for use because there is an awful lot of consumer and professional equipment out there which continues to use those in high current applications which one would expect they would not do if they were not suitable, were as appalling as some suggest. Every monitor I have with an external power brick uses 12V, 2A or 3A, with a barrel connector and I have never had any problems.
That is because barrel connectors are used in applications where it doesn't matter that they have (relatively) high contact resistance, as it doesn't matter that a fraction of a volt is lost in that contact resistance, for example the 12V 3A input may be used to feed an internal DC/DC regulator that can accept input voltages as low as say 10V. This is true for ALL applications where barrel connectors are used.
The energy dissipated in the connectors, can be dissipated in them, as they have relatively large mass.

Also, barrel connectors demand a high capacitance and large voltage bulk capacitor after them, as a reservoir for current peaks (for example 10.000uF 16V) and these are physically much too large to fit on the relatively tiny PI.


For the application that a PI uses the power connector for, a DC input connector with a very low contacts resistance is of paramount importance, as a drop of say 0.1Volt can cause the received voltage (after the input connector) to drop below the acceptable range of minimal 4.75 Volt.
And the PI also must do with a physically much smaller bulk capacitor of say 470uF 10Volt, so it cannot locally provide for large current pulses, but must draw these from the external supply, through the cable and connector.

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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 12:36 pm

feelslikeautumn wrote:
Wed Jun 13, 2018 11:57 am
Imperf3kt wrote:
Tue Jun 12, 2018 10:47 pm
Perhaps the next Pi should include pads we can solder to so as to completely avoid the micro USB port, while still retaining the polyfuse protection.
+1

Or some sort of header. The micro USB port is problematic even with an official power supply (for example I've had undervoltage warnings with no peripherals connected). It's crazy talk to deny there are issues with the choice of micro USB.
No one is denying there can be issues with microUSB, what people are saying is that there are no clearly better alternatives.

(Actually USB C would probably be better, IMO, but it's still expensive.)
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hippy
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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 3:24 pm

mahjongg wrote:
Wed Jun 13, 2018 12:17 pm
For the application that a PI uses the power connector for, a DC input connector with a very low contacts resistance is of paramount importance, as a drop of say 0.1Volt can cause the received voltage (after the input connector) to drop below the acceptable range of minimal 4.75 Volt.
So 5V input going in could afford a 0.25V drop before it even became potentially problematic but there's no need to be so defensive about the choice made for the Pi. I accept that the micro-USB is the de facto standard for 5V as stated earlier, that barrel connectors would not be appropriate for the Pi.

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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 3:30 pm

Imperf3kt wrote:
Tue Jun 12, 2018 10:47 pm
Perhaps the next Pi should include pads we can solder to so as to completely avoid the micro USB port, while still retaining the polyfuse protection.
Actually these solder pads do already exists, in the form of the test pads PP2 and PP3, see this schematic part of the published (abbreviated) schematic.
PP2 can be used to input +5V before the polyfuse, and PP3 to PP6 for GND.
microUSB and testpads PI3B+.PNG
microUSB and testpads PI3B+.PNG (10.65 KiB) Viewed 757 times

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mooblie
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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 5:25 pm

PLEASE PLEASE (as requested previously) could not the existing (and little used?) RUN and PEN pads be, if not replaced, but accompanied by a similar pair of DCIN and GND unpopulated pads? There is clearly board space, and the cost would be essentially zero.

Image

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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 7:00 pm

mooblie wrote:
Wed Jun 13, 2018 5:25 pm
could not the existing (and little used?) RUN and PEN pads be, if not replaced, but accompanied by a similar pair of DCIN and GND unpopulated pads?
RUN and PEN do have their place but it would be handy if it were a RUN+0V pair as it used to be on earlier Pi and, if adding 0V, one might as well add a 5V via poly fuse as well. Make it a 2x2 block, as on the Zeroes.

That would also be useful for connecting external circuitry which controls RUN/PEN and would need 5V/0V.

The test point pads are there but they are a pain to use and solder to, and aren't intended for wired powering.

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Re: Voltage normalised (0x00000000)

Wed Jun 13, 2018 8:05 pm

Just as an aside; the Pi Slice plus the resin.io Fin and other Compute Module carrier boards do use barrel jacks for their power input. For resin.io boards that allows 6V to 30V operation and therefore requires regulation to get 5V. Supporting a wide range of voltages reminded me that was the primary argument for preferring barrel connectors.

But that was some 7 years ago, before micro-USB for 5V had really established itself as the standard, before higher current, well regulated USB power supplies were widely available.

That emerging micro-USB standard and not needing regulation on board made it the right call to make, even if it does require manufacturing an official supply because many of the rest and cables aren't up to the job.

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Imperf3kt
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Re: Voltage normalised (0x00000000)

Thu Jun 14, 2018 12:10 am

If its insulting, then its an insult needing to be said. The truth hurts sometimes and nobody is perfect (not even the folk at the Raspberry Pi foundation)
You know what I find insulting? I find it insulting that people consider anything suggested has been suggested without thought and consideration.

None the less, it was not intended to be insulting and shouldn't be taken as such.

Regarding the polyfuse, there's very little chance people will buy one at $15+P&H to stick on something that already has one...
User experiencing technical difficulties.

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Re: Voltage normalised (0x00000000)

Thu Jun 14, 2018 10:38 am

Imperf3kt wrote:
Thu Jun 14, 2018 12:10 am
Regarding the polyfuse, there's very little chance people will buy one at $15+P&H to stick on something that already has one...
They seem to be £0.60 in one-off quantities at mouser ...

https://www.mouser.co.uk/ProductDetail/ ... 7pGyDhCQ==

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Re: Voltage normalised (0x00000000)

Thu Jun 14, 2018 10:56 am

Imperf3kt wrote:
Thu Jun 14, 2018 12:10 am
If its insulting, then its an insult needing to be said. The truth hurts sometimes and nobody is perfect (not even the folk at the Raspberry Pi foundation)
You know what I find insulting? I find it insulting that people consider anything suggested has been suggested without thought and consideration.

None the less, it was not intended to be insulting and shouldn't be taken as such.
Cannot find what you are referring to. If there is an issue with a post, even a mods, please report it.
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hippy
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Re: Voltage normalised (0x00000000)

Thu Jun 14, 2018 4:02 pm

jamesh wrote:
Thu Jun 14, 2018 10:56 am
If there is an issue with a post, even a mods, please report it.
Has the main forum rule, "the moderators are always right", been rescinded ?

viewtopic.php?t=131922#p880042

Milliways
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Re: Voltage normalised (0x00000000)

Fri Jun 15, 2018 2:03 am

hippy wrote:
Wed Jun 13, 2018 7:00 pm
RUN and PEN do have their place
What is the PEN supposed to be used for? I had assumed the RUN was as before, there seems to be no mention of PEN that I can find.

PEN seems to have 3V - which seems pointless.

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Re: Voltage normalised (0x00000000)

Fri Jun 15, 2018 3:47 am

Milliways wrote:
Fri Jun 15, 2018 2:03 am
hippy wrote:
Wed Jun 13, 2018 7:00 pm
RUN and PEN do have their place
What is the PEN supposed to be used for? I had assumed the RUN was as before, there seems to be no mention of PEN that I can find.

PEN seems to have 3V - which seems pointless.
PEN explained here: viewtopic.php?t=207961
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

Milliways
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Re: Voltage normalised (0x00000000)

Fri Jun 15, 2018 5:54 am

klricks wrote:
Fri Jun 15, 2018 3:47 am
Milliways wrote:
Fri Jun 15, 2018 2:03 am
hippy wrote:
Wed Jun 13, 2018 7:00 pm
RUN and PEN do have their place
What is the PEN supposed to be used for? I had assumed the RUN was as before, there seems to be no mention of PEN that I can find.

PEN seems to have 3V - which seems pointless.
PEN explained here: viewtopic.php?t=207961
The link contains a lot of speculation, but further study of the Pi3B+ schematic shows PEN connected to the GLOBAL EN pin of MxL7704.

The MxL7704 data sheet shows:-

GLOBAL EN Chip enable. When pulled low, shuts down entire chip after power down sequencing complete.

I also note the Power Good output 2 connects to the RUN pin.

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Re: Voltage normalised (0x00000000)

Fri Jun 15, 2018 6:17 am

hippy wrote:
Mon Jun 11, 2018 11:03 am
Milliways wrote:
Mon Jun 11, 2018 12:01 am


That is WHY most computers use the kind of voltage detector chip used in the Pi3 to hold the processor in reset until the voltage is OK - and we are talking mS not seconds.
Unfortunately it seems there is no timed hold-in-reset for the Pi, or, if there is, it's not long enough for my PSU.
I note the Power Good output 2 of the MxL7704 on the Pi3B+ connects to the RUN pin.

The events which cause this to be asserted are programmable, so its function is unclear, but it seems possible if not certain that the Pi would not start until the Voltage is OK.

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