3

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:

PCB Schematic

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

Here's a picture:

enter image description here

What am I doing wrong?

Joel Spolsky
  • 547
  • 1
  • 5
  • 17
  • 1
    I've used the ATSAMD21E18A + a bypass cap + USB connector with the Trinket M0 bootloader from Adafruit in a bare minimum board and it worked fine after flashing. Could try that bootloader, if it doesn't work you probably have a wiring problem. Note that Adafruit won't support anything but the E18 series due to hard coded memory map, so make sure you have that and not E17 or smaller. – user1850479 Dec 06 '21 at 22:28
  • 1
    The SAMD21 datasheet (pg 28) shows PA24 for USB D- and PA25 for USB D+; this appears to be correct in the breadboard image. This also matches @Mat's point above, but just note that PA24 is _pin_ 23, and PA25 is _pin_ 24 (potential confusion point there). – JYelton Dec 06 '21 at 23:19
  • 1
    You may also want to try shortening the USB lines as much as possible. – Armandas Dec 06 '21 at 23:53
  • Breadboards are unreliable crap - always suspect the breadboard. I'd double and triple check all connections with a multimeter, or preferably throw the damn things out the window and solder everything properly. – Lundin Dec 07 '21 at 07:50
  • Thanks for the advice everyone! At this point I really do think it’s either the breadboard or even the PCB where I used pretty thin traces, so I’m going to try putting everything on a single PCB and designing that more carefully. – Joel Spolsky Dec 08 '21 at 14:14

0 Answers0