[quote]Quote from kattle87 on October 30, 2011, 16:39
Well, does this mean that my phone actually asks for more power even when turned off?
Quite possibly, but it helps to remember that most people charge their phones with special chargers that came with said phone providing for a quick charge, these devices tend to work like other standard battery chargers and ignore the fact that it\'s a USB port (that is to say they charge for a short time at high mA, then a lower steady current, and finally a very low floating top off charge to keep things fresh). When it\'s connected to a computer, however, I\'ve noticed that my phones have tended to take an extremely long amount of time to charge even when powered off. If this is because it doesn\'t auto-negotiate, or because the 100 mA gives it enough power to turn on just enough to negotiate for more power, but 500 mA is still lower than the output of the charger that came with my phone... well I\'m sure that varies by manufacturer.
And there are some cables (according to some site, perhaps even wikipedia) in which the data lines are shorted, and I\'m expecting that the power cannot be negotiated when you have no data line? So I hope there are ways to power the Raspi out from a standard hub.
That again would be cables that came with the special charger shipped explicitly for phones. It essentially ignores the fact that it\'s usb and just uses a regular charger hooked up to a usb form factor. As such one might describe the charger as forcing the current down rather than the device requesting the increased draw.
BTW: the USB+ethernet hub posted by OP made me wonder: if a standard USB hub has 4 outputs (4xUSB or 3xUSB+LAN), what happened to the last USB on the internal raspi hub? (lan + 2xUSB + one gone missing?)
I ask because a 3xUSB out could really remove the need for an external USB hub for adecent chunk of users (especially people originally intended as an audience) (and I do understand this is not happening anytime soon).[/quote]
As Obart said, there\'s no hidden USB port I fear. The chip being use (LAN9152) is a combo usb hub and usb->ethernet adapter and while it might seem odd there\'s actually several reasons it\'s being used
1. By having the ethernet and usb on the same chip it both saves money and keeps the total size of the pcb down (which saves more money) and removes the need for additional data lines and possibly even another layer (which saves even more money!)
2. By using the 2 port model rather than the 4 port model they (are you ready for this?) save money
Not only is the chip cheaper and not only do they save money on not have to place the additional two ports on the board (thereby keeping the footprint down, etc, etc), but one thing we often forget is that the PCB is incredibly small, to add the 4 extra data lines and 4 extra power lines is an incredibly difficult task. Indeed, they already had to drive the layers from 4 to 6 layers. 8 lines would probably create the need for a seventh layer.
While these costs are undoubtedly under 10 dollars per board in the long run, on a project that is coming down to the penny to meet a low price point, each additional dollar adds up in a big way! Plus I\'d wager that most the applications a hobbyist would use a board in would require 2 or less usb ports (media center for TV, web server, proxy filter, arduino substitute, security system (just thought of that one
), the list goes on). Even for a desktop replacement, the only pinch point would be the printer, and if each board cost me an extra 5 bucks a pop, I\'d be better off buying a cheap print server and making my printer a network printer than having to pay an additional price on each board I planned on buying.
Well that was rather off topic, but I hope it answered your questions