Hello Nordic Community,
I am currently working on a project that involves a Garmin-style devices to display acceleration and velocity data, connected in ANT. I have some background in both software and hardware development and have purchased the Nordic nRF52840 Evaluation Board. I spent the past two weeks making the sensors work with the DK: so far so good 
I am sensing an SPI and I2C sensors, which will be placed in a separate PCB, connected through a Molex cable. I would love to have your opinion on this schematic before I start populating my PCB.
Things to note:
- for this first preproduction run of prototype PCBs, I'll be using a QFN-48 package, sinc I don't have a lot of GPIOs and I will hand solder the entire board. The QFN seems a bit more forgiving than the weird aQFN package :)
- I'll be using a 2 layers PCB to save costs
- this preproduction run serves to validate everything in my lab before moving to a compact, optimised solution. Hence the PCB will mostly use relatively large 0805 SMD packages and a lot of test point here and there for debug/testing purposes
I am left with some questions:
- I want the USB connector to charge the battery. I have based my design on the Thingy:52 schematic. Can you confirm this is the right way to do it? Are there any specific components or configurations I should be aware of to enable this safely?
- One of the difference with the Thingy layout wrt the battery is that the QFN package does not include VDHH, hence I have tied the battery voltage to VDD, is this correct?
- Programming wise, everything can be done via the debug connector, can you confirm? I assume I can use the nRF52840 DK board to program my custom PCB? Do I need to power down my board while the debug cable is connected to the DK? Don't want to fry it :)
- JLink: is this needed or again the nRF52840 DK is enough to perform simple flashing?
- Antenna wise, I have implemented the Thingy 52 strategy, with the usage of the 2450AT18B100E antenna. Is that a good approach? Do I need to fiddle around with traces length/impedances? I have to say I know very very very little about RF design
- Should I use external pull-up resistors on the I2C lines, or are they already integrated in the chip? My schematic currently has them (4.7k)
- I noticed TDS protection at the USB connector in the aQFN layout. However, if the QFN does not have enough pins with USB data lines, is TVS ESD protection still recommended? Note I've added it anyways in my schematic in the form of a DT2041 chip connected to the USB D+/D-
- Considering the QFN-48 Package: from looking at docs and forum posts, it seems less supported, and I’m concerned about compatibility. All my code so far has been developed on the DK board, which has the QIAA package. Can you confirm the main difference is just HW (diff number of GPIO, package, etc.), and that my QIAA software should work with the QFN?
General question:
- Let's say the board gets manufactured and populated correctly and it's ready to go. What would be the recommended starting or powering-up procedure to ensure everything initializes correctly? I assume I'll be using my nRF52840 DK to program/flash my custom PCB via the debug cable
Thanks so much for any guidance you can provide. I’m still in my first steps of RF design and there’s a lot to take in, so any tips or shared experiences would be really helpful. This project is a big learning opportunity for me, and I want to make sure I’m setting everything up correctly from the start.
Appreciate any insights from the community!
Thanks again!
