USB type C cable for power source

Thread Starter

Jammy27

Joined Feb 4, 2020
2
Hi, I started a home project of converting a Xbox into a retro game console. It's the first time I've done anything like this so learning as I go, the power supply to the raspberry pi 4 I have has a USB type C connection. I want to be able to strip a type C apart and wire it into a board which controls voltage and current. The reason I'm doing like this is I want to keep everything else the same in terms of power supply, then have everything housed inside the Xbox casing. Presumably all I need to do is trace the supply and ground wires to the cable and this should work? Or is there more to it than this? I don't seem to be able to find anything online that helps so just wondering if anyone on here may know.

Thanks in advance
 

Thread Starter

Jammy27

Joined Feb 4, 2020
2
Hi two hats,

Those listed in the link are different usb. I need the type C end I've managed to find a diagram of the pins, similar to what your link shows but there is more connections. My understanding is that all I'd need is the supply and ground from the wiring to supply power to the raspberry pi unit. If this is the connection for the main supply surely it won't use any of the other wires?

To me this would suggest I'd just need to link A1,B12,A12,B1 for the ground and A4,B9,A9,B4 for the supply and everything else would be no longer required?Screenshot_20200204-183331.png
 

Hartebeest

Joined Feb 17, 2020
5
I think there's almost certainly more to it than just the power and ground connections.
I'm trying to do something similar regarding powering an RPi4 from a non-standard power source.

According to sources such as this article (elsewhere on this forum), the USB-C standard includes a handshaking standard which relies on sensing of voltages on the CC1 and CC2 pins, onto which either 'end' of the connection applies a combination of pull-up or pull-down resistors. In plain vanilla applications (i.e. not exploiting the 'USB Power Delivery' extended voltage capabilities) this provides the powered device the means to 'tell' the power supply what level of charging current it is capable of consuming (at a fixed 5V nominal), so the power supply can set its current limit appropriately. If you don't provide the CC connection then the handshaking fails and the supply should either default to USB 2.0/3.0 current delivery (500mA or 900mA - neither of which will power a RPi4) or not provide power at all (as it is not detecting the connection). At the powered device end (your RPi4) an absence of sensed CC voltage might result in the device not even trying to power up.

By wiring a DIY cable to a fixed power supply without the defined pull-ups at the supply end you are circumventing this handshaking and while you may still be able to drive 5V into the RPi4 at up to 3A, I've yet to convince myself that the RPi4 would be happy. That said, there's been some controversy in how the RPi4 has implemented its pull-down(s) so maybe it's not so fussy with a non-smart supply source. Either way it's a risky approach.

I've just taken delivery of some USB-C connectors so my experiments have yet to begin. I'll let you know what I find out.
 

Hartebeest

Joined Feb 17, 2020
5
In addition to that in-forum article, I also found this other article (on a different forum) which provides some pull-up resistor values expected at the power source end. For the full 3A the standard value would be 10kΩ (to the 5V supply rail), and if they do turn out to be necessary there ought to be one of these 10kΩ pull-ups on each of the CC pins at the power source end.

I've yet to determine if that value is still correct, given the way the RPi4 pull-downs were implemented.
 

Hartebeest

Joined Feb 17, 2020
5
Correction to my comments in #4 above:
In plain vanilla applications (i.e. not exploiting the 'USB Power Delivery' extended voltage capabilities) this provides the powered device power supply the means to 'tell' the power supply powered device what level of charging current it is capable of consuming delivering (at a fixed 5V nominal), so the power supply can set its current limit appropriately.

Apologies for having confused which end had the pull-up resistors (I'm new to this stuff too...)
 

Marcus2012

Joined Feb 22, 2015
383
Afaik USB C cables contain an emarker IC moulded into the connector housing of the cable, this included Pi 4 power supplies iirc. When the Pi 4 was launched many USB C cables simply did not work with it, I never did find out if this was addressed eventually. The problem was board side however and frankly, it was silly for RPiF to use USB C configured with such limited connectivity. It is this emarker that coordinates the initial handshake and sets max current draw. Without it it is limited and probably won't supply enough.
 

Hartebeest

Joined Feb 17, 2020
5
Afaik USB C cables contain an emarker IC moulded into the connector housing of the cable, this included Pi 4 power supplies iirc. When the Pi 4 was launched many USB C cables simply did not work with it, I never did find out if this was addressed eventually. The problem was board side however and frankly, it was silly for RPiF to use USB C configured with such limited connectivity. It is this emarker that coordinates the initial handshake and sets max current draw. Without it it is limited and probably won't supply enough.
I don't think the situation is quite that bad (although still an embarrassment to Raspberry Pi Trading).
Only some USB-C cables (not including the RPi4 standard PSU) have this man-in-the-middle 'eMark' circuitry. It's only those eMark cables which don't work properly with RPi4, due to the incorrect configuration of pull-down resistors at the RPi4 board's power input which defeats an eMark circuit's handshaking. Other simpler USB-C cables without that eMark feature are still able to deliver the 1A-or-more needed by the RPi4, provided the power supply block at the source end is capable of delivering sufficient current and aren't as fussy about the handshake logic*. The higher current does not actually require the eMark circuit in the cable. The challenge is finding a cable that doesn't have an eMark circuit, as many of them are apparently not actually "marked" as such.

I found yet another link (in yet another forum) that examines the issue fairly deeply. The many comments below it make for interesting reading if you have an hour or two to spare to indulge in your in-depth research pleasure.

* - It's the uncertainty around this level of how fussy either end of the supply-sink pairing needs to be which will determine whether OP (Jammy27) can power his RPi4 from his XBox supply with no extra wiring.
 

Hartebeest

Joined Feb 17, 2020
5
Hi, I started a home project of converting a Xbox into a retro game console. ...
Is it a supply from an original-model XBox, an XBox One or something in between?
Not sure about original XBox, but AFAIK the XBox One has a 12V supply and a 5V supply. Obviously you'll need the 5V supply but it's only rated at 1A, I think. That might not be enough to reliably run your RPi4.
 
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