After breaking the z-axis connection on my first device I ordered a new KXPS5 accelerometer from crodnet on ebay. I really recommend this seller, he’s very cheap and sends things rapidly.
I quickly knocked together a circuit on veroboard and hooked up the base of a transistor to the freefall / motion interrupt pin to check it was working. It is remarkably sensitive, the LED flicks on if i drop my pen at one end of my desk when the device is at the other! I was quite pleased that everything was working well so i hooked it up to the I2C bus using the cable kit kindly supplied by www.andahammer.com. Using I2C tools i was able to set registers and read acceleration vectors without any trouble so i’m pretty sure everything is working well. I was a bit worried about exceeding the bus capacitance at first.
It turns out that i can still use the old device if i rely on the internal low pass filter. I was thinking of doing this anyway and using a Kalman filter to process the output. First i need to write a device driver so i’ve rapidly being trying to learn C. So far i’ve got a very basic kernel module up and running on the mini2440 🙂