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Building my own PCB based on QtPy schematic - USB not found
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Building my own PCB based on QtPy schematic - USB not found

by spolsky on Mon Dec 06, 2021 6:05 pm

I'm trying to build my own custom PCB based on an ATSAMD21E chip. I made a PCB breakout for the ATSAMD21E that just supports the reset button, a 3.3V voltage regulator, and a couple of capacitors.

After building the PCB with a fresh ATSAMD21E from Digikey, I connected it over a Segger JLink, and then flashed a bootloader onto the chip successfully using Microchip Studio. The bootloader I am using was Adafruit's QtPy bootloader, which uses the same chip as I am, also without an external crystal, so I thought that would work.

Unfortunately at this point I just get an error message "USB Device Not Recognized" instead of seeing a new USB device show up as expected.

Here is the schematic for my PCB:

schematic.png
schematic.png (52.72 KiB) Viewed 193 times


I mostly just copied this from Adafruit's schematic for the QtPy. I followed these instructions:

https://learn.adafruit.com/how-to-program-samd-bootloaders

for flashing the bootloader (which worked, I just can't see the USB port).

I have tried this with two different boards built from scratch with all separate components just in case it was a soldering problem, which did not solve the problem -- the second time the flashing of the bootloader worked fine again, and once again the USB device did not show up.

What am I doing wrong?

spolsky
 
Posts: 2
Joined: Thu Oct 11, 2018 6:47 pm

Re: Building my own PCB based on QtPy schematic - USB not fo

by danhalbert on Tue Dec 07, 2021 1:34 pm

You could try dumping the flash and verifying it looks like the flash on the QTPy. Also, make sure there are reasonable values for the fuses: if the fuses are set to all 1's, the board will trigger a watchdog reset every few seconds. There's a lot of discussion of fuse settings in the uf2 repo, e.g.: https://github.com/adafruit/uf2-samdx1/ ... -611128451

Other than that it's hard to say without debugging the board, making sure the design is OK, etc.

danhalbert
 
Posts: 2957
Joined: Tue Aug 08, 2017 12:37 pm

Re: Building my own PCB based on QtPy schematic - USB not fo

by spolsky on Wed Dec 08, 2021 10:14 am

Thanks for that advice! At this point I think there’s something wrong with my PCB design… but I can’t be sure. I definitely noticed that Lady Ada’s PCBs use much wider traces than I did, and I think the fact that some of my prototyping is on breadboards is causing problems too. I’m going to try designing a new PCB more carefully and see if that helps!

spolsky
 
Posts: 2
Joined: Thu Oct 11, 2018 6:47 pm

Please be positive and constructive with your questions and comments.