I have succesfully connected an MCP23017 to my Arduino Mega and got it to blink a LED using a 330 Ohm resistor. Now I am trying to drive the relay's on a Velleman K6714-16
I connected the output pin through a 330 ohm resistor to an input pin on the Velleman K6714-16 and connected the ground pin of the Velleman card to the common ground. For some reason this works for about 5 blinks and then the MCP23017 is blown up. If I use an Arduino digital output pin instead of an MCP23017 pin everything works fine.
After some further testing it seems the problem is of a different nature, the test with the blinking led seems to work for a few seconds and then stops blinking. After resetting the microcontroller it most of the time continues blinking until it stops again after a while.