jwatte
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Re: USB slave and power

Sat Aug 13, 2011 9:05 pm

If the power connector could be mini-USB, then there are tons of cheap, available power supplies. If it could also be used for USB slave mode, that would be icing. Does the controller support this? Could the current power input be replaced with mini USB at the same cost?

I think many USB power adapters can supply more than 500 mA. Else, the USB host ports might not get enough power...

(Note: I think hitting the $25 point is super important; more important than this request, so just food for thought)

AmyS3
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Re: USB slave and power

Sat Aug 13, 2011 9:59 pm

those usb power adapterswork on 5V while the raspi currently works with 6-20V. (if you dont need hdmi/usb you can power the board directly with 3.3V)
but the raspi dev team is considering to maybe changing it so you can power it with 5V.

for the mini usb connector, if you have enough soldering skills you will find a way to swap the parts.. :-)

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abishur
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Re: USB slave and power

Sun Aug 14, 2011 3:13 am

It's a good idea! Though I might be biased since I asked for the same thing :P I asked it on one of the threads discussing power supplies they discuss the overall issue (The specific post where they discus it is here) the basic gist is that a power supply that takes 5V and lets you also run 5V while at the same time offering a small amount of protection is much more expensive than a wide range 6-20V power supply :(
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Lob0426
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Re: USB slave and power

Sun Aug 14, 2011 5:48 am

The only problem I see with that is most of those mini USB power supplies are for things like charging phones and bluetooth. Have any of you looked to see what those put out for amps? I am guessing that for good stable power you will need about 7 watts from the power adapter.
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Re: USB slave and power

Sun Aug 14, 2011 8:31 am

500ma is the USB current specification - at 5v that's 2.5W. Some chargers throw out more, but that is non-standard.

The Videocore uses <250mW for most tasks (it amazingly low power for what it does), not sure about the Arm11 though -about 150mW I think @700. So that well inside the USB spec.
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Michael
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Re: USB slave and power

Sun Aug 14, 2011 10:08 am

As james mentions, the USB Battery Charging 1.2 suppliment to the USB 2.0 specification allows one to supply >500mA to a device (although the original intention was to charge the battery of a portable device, I guess one could use it to power a device).

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Lob0426
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Re: USB slave and power

Sun Aug 14, 2011 4:25 pm

I plan on using a wireless mouse/keyboard and a USB external HDD plus the Ethernet. The HDD alone pulls 1.5 to 4 watts in use (4 watts if you use a Y cable). I do not know what the mouse/keyboard pulls but it isn't much. This would probably be more than a mini USB charger can supply.

Could a mini USB connection be made to the board on the output side of the power controller? This would solve the problem but would have to be done by us as two connectors will be too expensive.
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Lob0426
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Re: USB slave and power

Thu Aug 18, 2011 10:27 pm

A model B will have 2 USB's each can be drawn at 500ma or 5 watts just for the USB's. I know this is a what if kind of answer. Then add the RasPi's own usage. I also try to supply power at 20% or so above actual usage to guarantee a stable working device even at max utilization. This also helps to have a longer lasting supply.
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miauto
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Re: USB slave and power

Mon Aug 22, 2011 2:19 pm

Quote from AmyS3 on August 13, 2011, 22:59
those usb power adapterswork on 5V while the raspi currently works with 6-20V. (if you dont need hdmi/usb you can power the board directly with 3.3V)
but the raspi dev team is considering to maybe changing it so you can power it with 5V.

for the mini usb connector, if you have enough soldering skills you will find a way to swap the parts.. :-)


So if we are connecting a wifi or bluetooth dongle, what kind of connection would you advice to us if we are planning to power it up with an external battery? could you design 2-pin on PCB to use with standar battery 2-pin connector? at least like this way, we will not have to deal with soldering stuff.

thank you very much in advance.

Thorbjoern
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Re: USB slave and power

Wed Oct 19, 2011 7:52 am

Quote from Lob0426 on August 14, 2011, 17:25
I plan on using a wireless mouse/keyboard and a USB external HDD plus the Ethernet. The HDD alone pulls 1.5 to 4 watts in use (4 watts if you use a Y cable). I do not know what the mouse/keyboard pulls but it isn't much. This would probably be more than a mini USB charger can supply.

Could a mini USB connection be made to the board on the output side of the power controller? This would solve the problem but would have to be done by us as two connectors will be too expensive.

You should not expect the ability to power additional units "downstream". Only use powered USB units in such a scenario or put in a sufficiently powered USB hub between your Pi and your disk/keyboard etc.

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Gert van Loo
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Re: USB slave and power

Wed Oct 19, 2011 9:47 am

There are some nice supplies out there from a big fruit company which supply 8-10W at 5V into a mini-USB plug. Strangely they seem to be affordable as well...

obarthelemy
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Re: USB slave and power

Wed Oct 19, 2011 10:22 am

Actually, not just Apple: all tablets I know are USB-powered (Nook Color, Touchpad...), with extra-strength usb PSUs. The Chinese have knock-offs, too. And some recent motherboards/laptops have those same extra-power USB ports, and they can charge while the PC is off, too.

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Re: USB slave and power

Wed Oct 19, 2011 10:54 am

Are these devices using the Battery Charging v1.2 spec?

http://www.usb.org/developers/.....class_docs

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Lob0426
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Re: USB slave and power

Wed Oct 19, 2011 10:10 pm

@Gert van Loo that would be nice if we had a final decision on the power to be supplied to the RasPi.

An iPad power supply at 10watts would power most uses of the the RasPi. If it is 5v. I think an iPhone power adapter will fall short at 5watts depending on what you connect to the RasPi. These power supplies are not very cheap at around $30 for the iPad power supply. If you have these type of supplies laying around then it is a good deal. Most phone chargers are in the same range as the one above. The cigarette lighter chargers seem to be in the 10watt range or more for those that are looking for a vehicle mounted system.
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Chris
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Re: USB slave and power

Fri Oct 21, 2011 2:12 pm

I think its safe to say this thread can be closed now lol.

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