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How does USB power work?

AnanasPaj
By AnanasPaj
in Hobby Electronics
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The IKEA lamp Riggad has a "dumb" USB 2.0 port in the front, and I wanna try to put data lines in it with a USB cord out the back, sorta like a USB hub/extender. Would it be fine to just attach the extra data wires to the port and run them out or do the USB devices need to communicate with the bus to negotiate power delivery?

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8 minutes ago, BlueScope819 said:

USB 2.0 the center two pins are power

nope nope nope nope, center pins are data. MBS (magic blue smoke) gets released if you connect those pins to power.

 

image.thumb.png.b6acb65f194f570e828defbcf54f78be.png

 

37 minutes ago, AnanasPaj said:

Would it be fine to just attach the extra data wires to the port and run them out or do the USB devices need to communicate with the bus to negotiate power delivery?

"Fast" chargers use the data lines to (passively) sense the current capabilities of the receiving devices (sensing the resistance across those pins, infinite resistance indicates normal 5V 500mA device).

 

I would recommend connecting all four pins to any given device in order that everything works properly and all MBS remains in its respective devices.

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Nah if the lamp provices the 5V USB power all you need are the two data lines.

You will probably need to replace the whole connector on the lamp though because usually those "ower only" USB ports don't have any data wires coming out at all.

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On 7/1/2020 at 3:08 AM, AbydosOne said:

nope nope nope nope, center pins are data. MBS (magic blue smoke) gets released if you connect those pins to power.

 

image.thumb.png.b6acb65f194f570e828defbcf54f78be.png

 

"Fast" chargers use the data lines to (passively) sense the current capabilities of the receiving devices (sensing the resistance across those pins, infinite resistance indicates normal 5V 500mA device).

 

I would recommend connecting all four pins to any given device in order that everything works properly and all MBS remains in its respective devices.

Wait, USB 2 Type A is always limited to 500mA by spec and USB 3 Type A to 900mA. Qualcom's Quick Charge is pushing this beyond USB spec and it takes specific power bricks for this. USB Power Delivery (PD) is specified in USB 3.1 spec and is to my knowledge tied to Type C sockets since it uses CC pin for sensing/negotiation. Power over USB is a mess once you go beyond the USB 3 spec with many manufacturers doing something beyond spec which then becomes proprietary.

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