Custom PCB Print + Assembly ?

D

demon_slayer

Level D
Hi folks, I run a small pikvm setup for my NAS since I don't live where my NAS lives and therefore need to be able to control/fix the NAS remotely in case I run into any issues.
For the pikvm, I need a custom usb cable which has power and data lines split, not going to go into any details but this is required for a diy pikvm setup.
Now the problem is that I designed the said cable and I'm guessing because of my lack of soldering skills / selection of wires, I always keep running into issues like low voltage on the pi or something else.

I then ordered the following splitter board from ebay splitter board and after waiting for more than a month and a half, it got lost in transit and I got refunded. I don't want to go this route again and hence reaching out wondering if someone can make such a board here in India and ship it to me.
Or better, create a usb data-power split cable.

Happy to discuss / provide more details on what I need.

Thanks !
 
Heisen said:
what ports do you need? All USB-C ? What is power requirement? Is 5V 3A enough?
Click to expand...
yes, all usb-c with 5V/3A DC since it will ultimately power a Raspberry Pi 4
GeeBee007 said:
Not sure if this works practically but theoritically maybe 3 USBC breaker boards and some soldering might help with this.
Click to expand...
This is something which will be at a remote location, and might need to be on 24x7, so trying to get something reliable which it won't be with my soldering skills.
 
You have to solder at some point, if you want to DIY it.

This is my Idea. You have to buy these USB-C breakout boards. 3 of them. Each costs Rupee 35.
7Semi USB-C Female Breakout

You can buy any breakout module of your choice, which ever seems easier to use. You have to connect them in following way.

You have to replace those tiny negotiation resistors on one board (specifically the data+power board) to the value of 10k each and connect them to VCC instead of GND. I got this info from here.

1729465860383.png


Now it's up to you how you want to make these connections either on a breadboard or directly, for breadboarding you have to solder the pin headers that come with each board into those holes, so each board can fit into the breadboard. Tip - mount the pin headers on opposite side for one of the board, either the power in board or the power + data board, so that when you mount them on breadboard their pins match exactly, see below what I mean.

You can use the mini breadboard it has enough slots to do all this and will make it very compact, also use smaller length cable USB-C if possible.

1729466649107.jpeg


I assume the external device to which you are connecting the RP4 is powered externally, the above only exposes the data lines on the USB-C port.

For power supply use something which can output 5V @ 3A, I recommend the official raspberry pi USB C power brick.

This is just my idea, if I were to do it, I would do it this way first, to see if it works. I can't confidently say that my circuit would work because it's on the breadboard.

But the parts are cheap, so maybe it's worth a try. Total cost should be around 300 including 3 boards, mini breadboard and it's jumper wires.
 
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Is powering the Pi through the GPIO pins an option?

If it is, you can use a USB-PD 5V trigger board and wire that to the GPIO pins with some readymade dupont wires that are easy to solder and use the type-c port as usual for USB Host.

Alternatively, you can use a micro-usb OTG splitter cable with a couple of inexpensive type-C to micro-usb port adapters. You might need to carefully cut out the power line from the otg side though, but that's not very difficult.
 
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rsaeon said:
Is powering the Pi through the GPIO pins an option?
Click to expand...
Yes it seems it can be powered through the GPIO pins, specially the power pins #2 for 5V and #6 for GND.

1729466833680.png


But there is no regulation or fuse protection to protect from over voltage and short circuit.

To the readers why the OP needs this weird solution to the problem.

On a Raspberry Pi 4 only the USB-C port that receives power is capable of acting as a USB Device. The other USB ports are capable only of acting as USB Hosts. Therefore a special cable must be used on the USB power port that it can simultaneously act as USB Device for the target host and receive external power from an power supply.
Click to expand...
 
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Heisen said:
You have to solder at some point, if you want to DIY it.

This is my Idea. You have to buy these USB-C breakout boards. 3 of them. Each costs Rupee 35.
7Semi USB-C Female Breakout

You can buy any breakout module of your choice, which ever seems easier to use. You have to connect them in following way.

You have to replace those tiny negotiation resistors on one board (specifically the data+power board) to the value of 10k each and connect them to VCC instead of GND. I got this info from here.

View attachment 211771

Now it's up to you how you want to make these connections either on a breadboard or directly, for breadboarding you have to solder the pin headers that come with each board into those holes, so each board can fit into the breadboard. Tip - mount the pin headers on opposite side for one of the board, either the power in board or the power + data board, so that when you mount them on breadboard their pins match exactly, see below what I mean.

You can use the mini breadboard it has enough slots to do all this and will make it very compact, also use smaller length cable USB-C if possible.

View attachment 211772

I assume the external device to which you are connecting the RP4 is powered externally, the above only exposes the data lines on the USB-C port.

For power supply use something which can output 5V @ 3A, I recommend the official raspberry pi USB C power brick.

This is just my idea, if I were to do it, I would do it this way first, to see if it works. I can't confidently say that my circuit would work because it's on the breadboard.

But the parts are cheap, so maybe it's worth a try. Total cost should be around 300 including 3 boards, mini breadboard and it's jumper wires.
Click to expand...
I would attempt this but replacing those tiny resistors is not something I think I can do.
 
demon_slayer said:
replacing those tiny resistors is not something I think I can do.
Click to expand...
You can just remove them, to add those 10k registers you can add through hole ones between the following on the breadboard itself.

CC1 <-> VBUS
CC2 <-> VBUS

So you only need soldering to just remove those tiny ones.
 
Heisen said:
You can just remove them, to add those 10k registers you can add through hole ones between the following on the breadboard itself.

CC1 <-> VBUS
CC2 <-> VBUS

So you only need soldering to just remove those tiny ones.
Click to expand...
Wouldn't I then need to short the resistor terminals for the ckt to be complete.
Also, what are these resistors and what role do they play in the ckt ?
 
demon_slayer said:
Wouldn't I then need to short the resistor terminals for the ckt to be complete.
Click to expand...
No you don't, because you yourself are adding new ones and those ones complete the circuit. So this it how it will look like.

1729507886186.png


demon_slayer said:
Also, what are these resistors and what role do they play in the ckt ?
Click to expand...
They are there for current negotiation between the source and the device, they play major role in the USB - C protocol.


If you look at the board that you ordered, that too have 7 resistors

1729508303832.png


If you decode those codes written on those resistor, you'll find out that :-

4 of them are 5.1k ohms
2 of them are 10k ohms
1 is just extra for the LED, we don't need this one.

So that configuration exactly matches the one we have on our bread board.
 
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