Let's mention the stupid mistakes first:

1. In the schematic, CN2 & CN3 are labeled as Yaesu interface, which is correct.  On the PCB layout however, these connectors are incorrectly labeled as Baofeng interface.
2. The distance between CN2 & CN3 should be 7.62mm, not 12mm as it is now.

With that out of the way, we can continue with what has been tested:

1. Sound output from handheld to Baofeng compatible headset
2. PTT : didn't work out-of-the-box.  Some patching needed.
3. Mic-input: patching needed here as well.
4. TNC-connection
   1. Recording audio output from HT with Audacity on Linux laptop.
   2. Sending audio from laptop to HT (patch needed).
   3. Next revision will have PTT-connected to RTS of the UART-interface as an option.
5. Programming cable functionality of the Yaesu interface works correctly using:
   1. Yaesu FT65-E radio
   2. CHIRP daily-20200622 software
   3. FTDI TTL-232R-3V3-WE UART-cable
   4. Tensility 10-02130 2.5mm audio jack cable

Inter distance Baofeng connectors

After receiving the Baofeng earbud, I noticed that the center distance of the Baofeng connectors is not 12mm as stated on the internet.  My earbud cable only had 10.8mm, while the clone cable only had 11.3mm.  So I guess 11mm will be closer to the truth.

Orientation Baofeng / Yaesu connectors

To be able to convert from one radio to the other, it must be possible to connect the Baofeng and the Yaesu connectors simultaneously.