nrdb
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Re: USB power

Mon Sep 19, 2011 12:08 am

Would it be possible to put a jumper on the Rpi so that you can choose if the Rpi supplies power to the USB port or takes power from it?

I was thinking this could be handy if you made the Rpi act as a USB client. I can think of a number of project ideas where that would be nice to try.

MDC
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Re: USB power

Mon Sep 19, 2011 12:20 am

I think this has been discussed before and I don't think it is possible. If I remember correctly the hardware won't allow it.

MDC
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Re: USB power

Mon Sep 19, 2011 12:21 am

Some one correct me if I am wrong as I am not a hardware person.

obarthelemy
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Re: USB power

Mon Sep 19, 2011 1:33 am

Not possible indeed.

hippy
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Re: USB power

Mon Sep 19, 2011 9:19 am

It really depends on the power supply circuitry and layout on the R-Pi plus the actual current drawn but it likely won't be possible to simply connect the R-Pi to a PC / Hub / Host with a USB cable and have it power the R-Pi without hardware modification of the R-Pi.

It also seems it won't be possible to do it and conform with official USB specifications but USB fans, coffee mug heaters and so on don't conform either.

If it can be done I expect people will show how to once they have R-Pi in their hands. I also expect there will be a robust discussion on why such solutions are bad ideas and not recommended against those who say it works for them :-)

langlo94
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Re: USB power

Mon Sep 19, 2011 6:41 pm

Well I know one way that could work, but you'll require some items:
- One of these:
- A powerjack that fits into the R-Pi.
- Some form of cuttation device, possibly a knife.
- Tools to connect the powerjack to the USB power supply.

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Lob0426
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Re: USB power

Mon Sep 19, 2011 11:36 pm

The final decision is due here shortly. Maybe a week or so.

That USB "Y" will work if you graft in the proper connector, if RasPi switches to 5volt only. If they switch to 5v that might even be the right connector on the cord. My personal opinion is that they already have the right power on the RasPi. It allows a wide variation of power supplies to make it easier to power it up. I also have plans if it goes 5v. We will have to wait and see.
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Vindicator
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Re: USB power

Tue Sep 20, 2011 2:28 am

I too would like to see it stay as is, wider diversity in voltage will make it easier for those it is really aimed at to use the device such as the poor youth on the block. I have everything I need to run a Raspi right now, but the targeted audience may not be so lucky and more choice of voltage is a higher success of powering the device for the masses it is targeted for, not us people who just want one to play with. IMHO

I have wall warts in a dozen different voltages and amperage's to hook it up and soldering equipment to convert the plug. But most of my neighbors kids probably don't. (SADLY)
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hippy
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Re: USB power

Tue Sep 20, 2011 9:00 am

Quote from Lob0426 on September 20, 2011, 00:36
My personal opinion is that they already have the right power on the RasPi. It allows a wide variation of power supplies to make it easier to power it up.

Absolutely agree. 5V 2A regulated walwarts are IME neither cheap nor easy to find whereas 9V 2A or 12V 2A can be found with many old or spare routers and hubs.

I can see an argument of cost and perhaps board space for making the R-Pi 5V input only but that's really moving cost off the board and to elsewhere if one doesn't have a 5V supply or wishes to use battery power.

Not all "5V" walwarts are regulated and some can put out over 5V which risks damaging the R-Pi and anything connected to it.

IMO it's far better to allow a wide range of input voltage and let those who know what they are doing hack it about as they wish rather than impose very specific requirements on people who don't fully understand what they are doing.

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