obarthelemy
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Re: What size power plug ?

Wed Aug 17, 2011 5:34 am

Do we already what size coax jack the power plug will use, so that I can start scrounging around ?

Michael
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Re: What size power plug ?

Wed Aug 17, 2011 8:00 am

I don't believe the R.Pi team have made a final decision about the power input yet. There were a couple of comments on the forum about the relative merits of fixed input voltage vs flexible input voltage with a few people asking for the ability to power the board via USB.

If they go for fixed 5v and not a mini-USB jack, it would almost certainly be 2.5mm inner dimension, 5.5mm outer dimension. If they go for 6-16v, it would almost certainly be the de-facto standard 12v jack: 2.1mm inner dimension, 5.5mm outer dimension. Centre positive.

obarthelemy
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Re: What size power plug ?

Wed Aug 17, 2011 9:02 am

Thanks. USB would be great indeed.

gerits
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Re: What size power plug ?

Wed Aug 17, 2011 9:48 am

Why USB? Isn't it supposed to be a stand alone computer...

troll science: connect usb out to usb power => infinite power

obarthelemy
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Re: What size power plug ?

Wed Aug 17, 2011 11:20 am

USB because
1- there's plenty of these PSUs laying about, making it easier to scavenge one for free if you don't use a USB hub.
2- I expect many Pis will be connected to a USB hub: the Model A won't even let you use a mouse and keyboard at the same time, plus wifi, hard disk... so we could power the hub (which we will have to do in quite a few cases anyway), and have the Pi leech power off the hub, instead of having a power brick for the hub PLUS one for the Pi.
3- Having power to the hub is better, or even required as soon as you connect thirsty stuff to it. So worst case scenario: 1 power brick, but to the hub instead of to the Pi, so we gain good power to the hub. Best case scenario: 1 power brick to the hub, instead of two (Hub and Pi).

ShiftPlusOne
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Re: What size power plug ?

Wed Aug 17, 2011 11:48 am

Is it even possible for a host USB port to sink current from a USB hub and use the power?

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Lob0426
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Re: What size power plug ?

Wed Aug 17, 2011 12:19 pm

Yes you can supply the RasPi through the USB port. There four lines in USB 2.0 port, 5v-,5v+,data- and data+. There is a limit in the specs at 500ma but there are non spec devices that use more than that. You also can use a "Y" connector it has one plug with four lines for full USB and one plug with only the power, this allows a draw up to 1amp off of two USB ports. the RasPi is reported at 1watt draw, a single port can supply 2.5 watts. If you power the RasPi through a hub you will not be drawing power through the RasPi. Of course in the B model you have two ports, if you use USB to power it you would not be able to draw power for a device from the second USB. Drawing current for the device might overdraw and leave none for the RasPi. This would be an unstable arrangement at best.

I am hoping for the 12v but can work with it either way. Anyone have a diagram or a link to a board that is a nice, safe 12v to 5v drop? Probably something in spark fun I would guess.
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Bloodred
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Re: What size power plug ?

Wed Aug 17, 2011 1:10 pm

Considering the low power draw of the RasPi itself, I believe a LM7805 regulator and a few capacitors to smooth out any dips should do fine to provide 5V from 12V.

jamesh
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Re: What size power plug ?

Wed Aug 17, 2011 3:00 pm

Quote from ShiftPlusOne on August 17, 2011, 12:48
Is it even possible for a host USB port to sink current from a USB hub and use the power?

Good point - the Raspi is a HOST, which would normally be the end supplying the power. Powered USB hubs won't put out power on the input side, because that would conflict with any power the host was supplying.

But I don't know much about USB tbh.
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Lob0426
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Re: What size power plug ?

Thu Aug 18, 2011 5:31 am

Not sure either. There may be diodes, when it is a host, that prevent power coming in. If a USB port is dedicated as a power input only it works. Example they decide to go with a mini USB instead of the 6 to 20 volt barrel connector. In other posts it has been brought up that the power input may be changed.

Maybe when Eben has a moment, he can answer this for us.
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Re: What size power plug ?

Thu Aug 18, 2011 5:48 am

I don't know what this means, if anything, but when I turn off my computer and keep the USB hub plugged in and powered, one of the fans spins. =/

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Lob0426
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Re: What size power plug ?

Thu Aug 18, 2011 10:50 pm

Found this question to and statement from Eben:

Question: How many USB does the BCMxxxx support directly? Is it capable of both host and device modes?
Answer: One USB 2.0 port. We do support both device and host mode, though only host mode will be supported in software at launch.

So the RasPi is capable of operating in host or device mode. May have to modify the software to enable device mode. Powering the RasPi from USB is indeed possible.
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Gert van Loo
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Re: What size power plug ?

Fri Aug 19, 2011 11:42 am

I will have to talk to Eben about that!
On model B both USBs comes from the LN9512 and that as far as I know only supports host mode. I have to read the data sheet again. T

sparkly1982
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Re: What size power plug ?

Fri Aug 26, 2011 3:35 pm

Could the board be powered with a microUSB connector? As already mentioned there are loads of mains adaptors already about for this. Alternatively, a port from a powered USB hub could be sacrificed to power the RasPi.

berni
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Re: What size power plug ?

Sun Aug 28, 2011 8:39 am

Even if the R-Pi supports both device and host mode, I don't think it can do both at the same time.

In my opinion a second psu port is no problem but a second brick is. So it would be nice to implement a micro USB port or something like that just for powering beside the normal USB port for connecting to other devices.

obarthelemy
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Re: What size power plug ?

Sun Aug 28, 2011 9:43 am

Quote from ShiftPlusOne on August 18, 2011, 06:48
I don't know what this means, if anything, but when I turn off my computer and keep the USB hub plugged in and powered, one of the fans spins. =/

Some more recent motherboards have firmware that detects when a device is been charged via USB, and keep the charge going even with the PC off (or even, in Gigabyte's case, can provide much more power than usual, even enough for charging an iPad, 10w I think;maybe others do that too now). Maybe the fan spinning is a side effect of that.

obarthelemy
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Re: What size power plug ?

Sun Aug 28, 2011 9:44 am

Also, Yep, I was not thinking of a full-featured 'device' USB port on the Pi, just of a USB-format connector to suck in USB-level power from. No data transfers, just power.

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