Some years ago I posted article describing Universal CAT and programming USB to RS232 TTL interface for ham radio that I made.
Here is small update, adapter for YAESU FT-8900, FT-8800 and alike radios.
FT-8900 and FT-8800 and some other Yaesu radios use two wire interface. One wire is ground and other is both RX and TX. This is also known as CIV-I interface used in Icom radios.
CIV-I interface is quite simple. There is a diode (universal like 1N14148) connecting RX and TX, oriented cathode toward TX, with one 10K pull up resistor to 5V on RX. Here is schematics:
However, I found out that YAESU FT-8900 already provides pull up voltage on PKS line, so, there is no need for 10K pull up resistor. Single diode connecting RX and TX is enough. That allowed me to make simple adapter that connects to my universal interface that provides only RX, TX and GND. Diode fits within 3.5 mm connector.
If you do not have mini din 6 pin connector, you may use cable salvaged from old PS/2 mouse (one with green PS/2 connector). Use non isolated wire as ground (it is connected to metallic shield of the connector not actual GND pin but it does not matter as on radio GND pin is connected to the shield) and red wire for PKS signal.
Finally, I am able to program my Yaesu FT-8900 using Chirp. Previously, I tried two factory made cables that did not work. I actually thought my radio was damaged but recently fellow ham Milan YU1ZZ managed to program other radio using his factory made CIV-I interface, which attracted my attention. We tried his interface with my radio and it worked so it was A-HA! moment. Radio works, cables I tried were problematic.