Somehow some of our RAK4631 USB is no longer detectable from any host computer (I assume the USB is damaged) but we managed to program new firmware using JLink directly to the SWD pins.
Sometime later, the RAK4631 can no longer boot the firmware that I flashed. The JFlash app shows no signs of error, so I assume the flash is OK.
Currently, the board is constantly doing some kind of breathing animation on the green LED even after I flashed a firmware that will turn on the blue LED (it stays off the entire time).
I’m wondering if anyone has experienced a similar thing at some point and if you have, what did you do to make it work again?
A breathing green LED shows that the device is in bootloader mode. In this mode it should be detected as a USB serial device and be ready to be flashed with a firmware over USB.
The USB interface is inside the nRF52 chip, not an external chip, so it sounds strange to me that it could be damaged and the rest of the nRF52 still works.
Do you have any other modules connected on the Base Board together with the RAK4631?
If yes, did you try to unplug them and see if it changes anything?
Is this happening with one RAK4631 only?
Do you have other Base Boards that you could use to check the RAK4631?
The custom-made PCB only adds sensors that are not available in WisBlock line products. I don’t remember exactly which IOs are used, but I2C and GPIOs are definitely used. This board is powered by a LiPo battery.
Anyway, the problem is caused by the damaged nRF52840. We have more than 10 devices and all seems working well.
We exposed POGO pins that connect D+ D- GND and VCC of USB to the RAK4631 since we were unable to expose a MicroUSB port directly on our device’s enclosure and somehow I managed to short the GND and VCC for a very short time.
The rest of the electronic parts were unaffected. We replaced the RAK4631 and everything worked as expected.