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Intermittent booting into DFU mode -- Bluefruit SPI friend
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Intermittent booting into DFU mode -- Bluefruit SPI friend

by hristo.staykov on Sun Jun 20, 2021 12:39 pm

In my keyboard, I am using a mdbt40-256rv3 bluetooth module desoldered from a Bluefruit SPI friend flashed with BLESPIFRIEND 0.6.7. I am certain that my PCB is correct, as I have been using this design for the past two years with no problems. I just had to solder a new module onto a different PCB (after the old one broke) and I run into the following weird behaviours:

- The module boots into DFU mode at random. Otherwise, the red LED flashes to indicate it's in DFU mode, and holding the DFU pin low to perform a factory reset does not seem to do anything.
- DFU mode works as expected -- I can connect with the Bluefruit Connect App and flash firmware.
- As of minutes ago (after I reflashed the firmware with DFU), when not in DFU mode, the connection LED is blinking irregularly (even when connected) , and I had trouble pairing to some devices. DFU mode still works alright (even when I don't want to be in DFU mode) and connection LED works properly there.
- I also tried flashing to the latest version (0.8.1) but still observe the same behaviours.

I verified that there are no shorts, that the DFU pin (P0.07 / Pin 7) is not connected to GND, and even soldered a 10k pull-up to 3.3v. I also checked that all other pins are connected where they should be. I wonder if anyone at Adafruit has experienced this when working with the Bluefruit SPI Friends / BLE Feathers. I did not do my part to test the module before transferring it to my own board, but I highly doubt that it was broken in the first place. Could it be that the heat damaged it in a certain way?
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Re: Intermittent booting into DFU mode -- Bluefruit SPI frie

by franklin97355 on Sun Jun 20, 2021 3:18 pm

Can you post pictures of the module and your PCB? If you include a schematic of you board it would also be helpful.

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Re: Intermittent booting into DFU mode -- Bluefruit SPI frie

by hristo.staykov on Mon Jun 21, 2021 12:48 pm

@franklin97355 sure, here are some photos of my PCB (splitting this in multiple posts because there's an upload limit):

DSC07268 copy.JPG
DSC07268 copy.JPG (195.69 KiB) Viewed 84 times

DSC07265 copy.JPG
DSC07265 copy.JPG (238.39 KiB) Viewed 84 times

DSC07269 copy.JPG
DSC07269 copy.JPG (222.77 KiB) Viewed 84 times
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Posts: 6
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Re: Intermittent booting into DFU mode -- Bluefruit SPI frie

by hristo.staykov on Mon Jun 21, 2021 1:06 pm

Photos of PCB, contd:
DSC07270 copy.JPG
DSC07270 copy.JPG (198.77 KiB) Viewed 83 times

DSC07274 copy.JPG
DSC07274 copy.JPG (172.91 KiB) Viewed 83 times


The PCB itself is based on the schematic for the 32u4 Feather BLE:
Screenshot 2021-06-21 at 19.37.14.png
Screenshot 2021-06-21 at 19.37.14.png (627.77 KiB) Viewed 83 times

The full schematic is available / pcb at https://github.com/hristost/merp-pcb.

I believe that the connection LED blinking is an indication of the board attempting to do a factory reset due to it thinking the DFU pin is low. Once connected to a computer, it's lit all the time.
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Re: Intermittent booting into DFU mode -- Bluefruit SPI frie

by hristo.staykov on Tue Jun 22, 2021 5:14 pm

I also measured the voltage at the DFU pin -- it's around 1.5V, which is a HIGH? If I recall correctly, the module runs on 1.8V internally.
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