So, I finally got around to test the PS2 interface prototype. I made a simple test program that only checks for the interrupt and then prints the key pressed value and connected the board up to a Arduino Mega and turned on the power. I gave me some spurious interrupts but I was not surprised, after all, it is a prototype hooked up with test wires. So I decided to connect a keyboard.
That is when the smell and pop came… Nooo….
I unplugged everything, but the Arduino was beyond saving.
So back to the schematics and looking at footprints. And low and behold, the footprint for the PS2 connector was mirrored. Which means that when I plugged in the keyboard I actually short circuited VCC and GND. And that is not something an Arduino likes.
This is why we make the small prototype boards to test things. To build a new µLind prototype board would have been more expensive than an Arduino.