@manuelbl that is great. I wish I could whip up a nice board like that. I will probably just solder the SWDCLK and SWDIO connections and use the boards GND and RESET and plugin the board for 3V3. That should be enough for what I am trying to do.
Really glad you shared what you do. Great to know that PlatformIO can do some serious debugging. I am not at that point yet, but really good to know it is an option.
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Yes I should be able to fix my broken Nano 33 BLE Sense by restoring the bootloader, (I flashed working Nordic software to it but missed the step in the .ld file to put the bootloader at the correct address 
)
MEMORY
{
FLASH (rx) : ORIGIN = 0x10000, LENGTH = 0xf0000
RAM (rwx) : ORIGIN = 0x20000000, LENGTH = 0x40000
}
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I am just trying to simplify the workflow for anyone wanting to use various nrf52840 boards.
The Nordic board is cheap and connects well to Openthread. The Arduino Nano 33 BLE Sense board has all those sensors. The Particle boards simply because I have a class set of them. (The Particle Xenon is just another cheap BLE board, but the Argon has an ESP32 with the nRF52840 SOC giving a few more interesting options.)
Ideally when PlatformIO has all of these working that solves the problem, however in the mean time I am going to look into trying different bootloaders and seeing what I can get working. The final result might be as boring as: use Arduino for Arduino, Nordic for Nordic, Particle for Particle Mesh.
Or things might get more interesting such as the Arduino bootloader works on all three with a few pin reassignments and go from there.
Anyway thanks @manuelbl for posting, what you have made with all it’s connectors would make a nice little build for a class or small group assignment. Got any extra boards?