Solution to uart to usb problem
I have just read through pages 1-8 of this thread. I might have a solution to your problems.
Uart stands for Universal Asynchronous Receive and Transmit. It is TTL logic for +5v for high and 0v for low. It is a serial interface.
Did you guys know that UART and the serial interface for the pc are exactly the same? Except you need to do voltage conversion using a max32 chip. You need to convert the +5v high to +10v and the 0v low to -10v. Then just plug the data lines into your serial port and viola.
Also, there are already converters made with drivers for convertering between spi, uart, and i2c all to usb. The links are below.
Those above links can the serial-usb translation inside the housing. But this next link might be exactly what your looking for. A serial to usb cord.
Also, if you want to be ambitious, they make wireless ttl uart modules.
This way, you can add a battery pack and use the keyboard wirelessly by itself. Then use the usb dongle to decode the signal and translate that into commands. I hope this info i have shown you help you guys.