i am trying to add an USB port to my Archer C6 v3 which is powered by MediaTek7621DAT CPU, it's datasheet shows that is supports both UB3.0 and 2.0 protocol. When I opened the Router I found it has a unpopulated USB connector space in the PCB. Infect a large part of the board is unpopulated. Ref: https://openwrt.org/toh/tp-link/archer_c6_v3
I know R989 and R990 designators are space for resistors
D1 probably means Data Line
But i could not figure out what those T9 and T10 means but hey connects to ground.
There is another problem the VCC of the USB pin has no power.
Some article says the VCC must be connected to the board even if we give it external power so i have to stop.
Then i found out the Archer c6U has same processor and a USB 2.0 port at the exact same area.
so i desperately searched for a picture of its motherboard. but i could not find any. So i am stuck again.
I am sorry if i have broken any rules i am unaware of by posting this please guide me though.
EDIT: I found out T9, T10 are TVS diodes for ESD protection. i think ESD401 from Mouser is a suitable TVS diode for those pads.
On USB-host, there should be 15k pull-down resistors on D+ and D-, check if those traces have such somewhere and if not, then they're most likely supposed to be on those pads there.
Thanks for replying,
I was thinking the same, however, when I checked i found no pull-down resistor on D+, D- line.
I am sure about T9, T10 pads are for TVS diodes for ESD protection.
The R990, R989 cant be pull-down resistors since they are in series on the D+, D- line.
so i was confused. then i found another board that uses the same Processor MediaTek7621DA and has a USB port. whish does not have any component on the data line whatsoever. here I traced the d+ and made an animation for easier understanding
In my opinion, this CPU might have an Internal pull-down(IPD) Resistor.
Thank you so much!
Although the small components are blurred out because of the image size but at least now I have an idea.
Even if you can identify the components, you need to purchase and assemble them to the board (I wouldn't dare to solder SMD that of size), and possibly compile your own image.
Of course, if you are up for tinkering, instead of that SMD SMPS stuff, you could just bodge together a 5V supply with a linear LDO 5V regulator with minimum effort.
However, I wonder if all that trouble is worth the effort, when you can simply get a device with USB in the first place. For me, USB is so universal (that's what the U stands for:) that it is a MUST when selecting a device for OpenWrt.
Yes, you are right, I should just get a 12V-5v step-down module or an LDO 5V regulator. However, as the Archer C6U also uses a 12V 1A power supply with the same hardware I think I can connect it directly without an external power supply.
The Archer C6U and Archer C6 seem to have identical hardware to me, shouldn't its images be interchangeable with C6? as we already have an OpenWrt image for that router maybe I don't have to go through the compilation process?
I agree I should have bought a device with a USB in it in the first place. But in this process, I am learning new stuff which is fun.
Yeah, some SoCs do. All the better for you, of course, because you don't strictly need the TVS-diodes, either, to test the USB! Can always chuck them on later on, if you feel like it.
Compare the two devices' DTS-files and see, if the partition layout and everything else is the same? If the only differences come from the USB, then you should, indeed, be good to go.
On the other hand, it's not that difficult to compile an image from scratch, either. The hardest part is having to wait patiently for the compilation to finish
I don't particularly enjoy working with that small ones, but they're still entirely doable; just gotta be careful not to accidentally flick them away. The hardest part of it is being able to see jack sh*t -- I'm blind as a bat without glasses and even with them, I still have bad eyesight
In my own projects, I prefer to use 0603 or larger components, just for the lesser amount of aggravation. Can't read the markings, but eh, that's what magnifying glasses are for.