That's the diagram I used. I just wired a ps2 cable into the switches of a joypad with, like you say, 2 diodes connecting the fire & direction lines.
After not touching this project for three years, I recently came across a half dozen PC compatible joypads that were on their way to recycling despite being fully functional. My heart said that electronics want to be rescued and repurposed, so I took care of them.
Some modding will be required on the joypad PCB due to how those pads wirk on the PC. Now I thought I'd be clever and snip off a PS/2 cable from a used up keyboard. but I soon realized that the standard wiring for both PS/2 keyboards and mice is to only use four of the six pins, while the Sord M5 obviously uses all six pins.
When you made your hack, did you start off with solderable 6-pin mini-DIN connectors and put your own cable onto it, or did you happen to come across some used keyboard where the manufacturer actually connected all six wires despite two of them weren't needed? Since the typical keyboard and mice connectors are moulded, it doesn't work out so well for me to hack it open and solder, I'd better get some fresh connectors in that case.
