Been a while since I've updated this. I'm using it lots though as a serial terminal and general embedded linux test bed. Makes an appearance with my Nixie Pipe  too: 

Back to this project though: through using it I realised I had the wrong gender termination for a DTE (I had a DCE), which meant using nasty adaptors/null modem stuff. I replaced it with the correct, male DB9. It works well, because the utility GPIO DB9 is female, so there is no chance of connecting RS232 levels to the wrong port. 

For the utility GPIO output, I also made a simple breakout board. The board includes headers for RX/TX, I2C, PWM and 5V/GND of the Pi, an LED status and most useful of all, a micro USB to power the WT-220. This means it can be powered like a standard RPi, rather than a DC jack. 

Since I've had some enquires, I've added the WT-220 to my shop. Very limited numbers will be made and it takes quite a bit of time so it is priced accordingly. 

https://shop.jbrengineering.co.uk/product/whitterm-220/