Next lot of PCBs are in. These ones fixed the wiring of the level shifter IC so that I can actually use the header pins! I also made the SWIO test point a little larger.

Unfortunately, I hastily sent the order before making any other changes. 

After looking at the board again, I subsequently made additional changes to the layout to improve the board. I moved the I2C pullup resistors close to the QWIIC connector, which gives me a bit more room for the level shifter and other resistors near the header. I also added a little more space between the components in the RF path, to reduce the chance of solder bridging. 

I'm sure there will be further changes before another respin, so I'll try and keep track of what I've changed. 

Evolved project ideas.

Considering the CH32V003's main feature is it's affordability, it doesn't quite make sense to match it to a $12AUD RF Transceiver ( in single unit qty). True, it goes down to $9AUD in units of 100, but that is still way more than the microcontroller cost. There are other Silabs transceiver ICs with lower output power that are slightly cheaper, but we're only talking a few dollars. 

One option may be to link the CH32v003 with the CMT2300A Transceiver from CMOSTEK (Wuxi Zetai Microelectronics Co., Ltd.) CMOSTEK appears to be a fabless semiconductor company. The chip is available from LCSC for under $2AUD, but it appears to come from HOPE RF, who also manufacture Transceiver ICs that are almost identical to the Silabs Si4463 ( i.e. the RF26W on the RFM26W module). The datasheet for the HopeRF module is almost identical to the Silabs one. The CMT2300AW chip from HopeRF seems to be identical to the CMT2300A from HopeRF.

The specifications for the CMT2300A seem similar enough to the Si4463., but unfortunately the registers are completely different, so there's no overlap in code. 

Another option using Silabs chips is to use the Si4460, which only has 13dBm output power. Rather than using discrete components in the matching circuit, Johansen Technology make a single component that contains all the required attributes for the Si4460 - the 0433BM41A0019001E . This would make the PCB much more compact, but have lower performance. 

The software side is not my strongest suit, so that remains the biggest hurdle. Anyone out there that's familiar with this MCU is welcome to assist!!