Just spent 3 hours converting a V3 board to work with the new feather (nRF52840)[https://www.adafruit.com/product/4062]. The conversion worked but it was utterly pointless.
TL;DR - Stick with V4 board + nrf52832. 840 offers no extra benefit while consuming a ton more power.
- Physical pin location change - A6 to AREF
- Lost a second 3.3V OUTPUT - Only get one on the 840
- Can't seem to use designated pins for GPIO - TX/RX, SCL/SDA etc.
The differences was enough to require changes in the firmware as well as cutting 4-5 traces and re-wiring the board. Unfortunately after all that, we still don't get extra pins when compared to the 832 because the 840 doesn't let you use all the pins as GPIO.
At this stage, I invested a good 2 hours of my Sunday, so I may as well finish it and see if there might be any benefits in performance / power consumption.
nRF52840 Eats A Lot More Current
The 832 only used about ~2.4mA when powered (ready to type). Whereas the 840 used a mind-boggling ~4.1mA. Over 70% increase in power consumption. Looking at the forums (adafruit, nordic, nrf52 github), it appears that I'm not the only one puzzled (and annoyed) by this surprise.
In other words...
I wasted a Sunday morning so you didn't have to. Get your hands on the (old feather)[https://www.adafruit.com/product/3406] if you're trying to build this.