AssetBurned
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USB-C Power and data to Zero OTG

Sat Aug 04, 2018 11:10 am

Hi,

I wonder why no one developed a board such as the USB Stem that allows the pi zero to be connected to USB-C.
I saw boards where you can just make use of the USB 2.0 lines and then forward it to whatever you want to build. But how about telling the USB-C port to also provide the 2 amp or even 3?

Or could that be easily done by setting that as part of the USB gadget functionality?

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W. H. Heydt
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Re: USB-C Power and data to Zero OTG

Wed Aug 08, 2018 3:06 am

You can do both power and data over the "data" micro-USB connector on a Pi0 or Pi0W. The power lines are common to both connectors. There isn't a lot of point to providing a Pi0/Pi0W with 2+A as the board will run flat out on less than 200mA

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Imperf3kt
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Re: USB-C Power and data to Zero OTG

Wed Aug 08, 2018 3:49 am

Maybe because male Micro-B USB to female USB-C adaptors and cables already exist?
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AssetBurned
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Re: USB-C Power and data to Zero OTG

Mon Aug 20, 2018 10:07 pm

These answers show that the concept of USB-C is not fully understood

A micro USB to USB-C adapter doesn't negotiate the power provided to the USB device. Also this can not easily be done by setting up the Zero as USB Gadget and just telling the host "I need more power".

Also that the Zero needs only 200mAh is ... well up to discussion and really depends on what you want to do with it and what have you hooked up to it. At least with the USB gadget functionality you can use up to 500mAh.

After reading up more about USB-PD and USB-C the initial question for up to 3A is indeed wrong. more realistically would be 900mAh as the default max there. Everything else would require more Voltage, that on the other hand would make the circuit more complicated as you would now have a step down as well.

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Imperf3kt
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Re: USB-C Power and data to Zero OTG

Tue Aug 21, 2018 12:48 am

A Pi will not 'negotiate' how much current it gets from any source. It draws what it needs, from what is available.
If you use a USB-C cable with an appropriate Micro USB-B adaptor, you will get 5v @ whatever amperage the power source (and cables) is capable of. If your power source is a "smart" USB charger, then the Pi will only see the "slow charge" setting.
Using USB-C to get more current is silly and not going to do what you think.
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AssetBurned
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Re: USB-C Power and data to Zero OTG

Mon Aug 27, 2018 12:05 am

Slow charge as you describe would be the default value of that particular USB interface.500mA on a normal USB connector and 900mA on a type C connector.
A proper USB charger that does negotiating with the device could provide more depending on which Power Delivery standard it follows.

However it also depends on the cable. That is correct. A normal USB cable (4 lines + shield) would be considered dumb and only the default value can be used.
Cable with an additional line can carry more (assuming the actual copper has stage right proportions to handle proper currents).

Going for the nagotiating part. If the Zero runs as USB gadget you submit your power requests to the OS and (depending on the hardware you use) the Host provides you with that amount of power. However that caps out at 500mA (or 900 on type C) and then you need specific hardware that can handle the negotiation as it is done here via USB protocol directly and not via some fancy software stuff running as data packages.

For everyone who is more interested into this topic... there are some boards available on Tindie.
The USB PD breakout board from reclaimer labs does exactly what I am looking for.
If you try it out don’t forget you should not put more the 5V on that second USB port. Your hardware won’t like it.

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Imperf3kt
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Re: USB-C Power and data to Zero OTG

Mon Aug 27, 2018 12:27 am

The assumption there is that a Pi Zero has data lines on the power connector - it doesn't.
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