This may not be what you are looking for, but as an early electronics project I made a pressure pad attached to the Pi. It wasn't very difficult at all electronics wise, I just had a plastic box lid which pushed down a DVD case when stepped on
. The DVD just rested on a push button. It used just three pins, ground, 3.3v constant and a GPIO pin. More recently, I updated it to post to a web server and send email alerts, without much difficulty. All the electronics you need are available on Amazon here http://www.amazon.co.uk/Electronic-Star ... B0082LD2B8
(I used a Raspberry Pi Electornic Starter Kit A from SK Pang), and if you need any assistance I can give you some advice. I used the Raspberry Pi Guy's tutorials and the Raspberry Pi Low-Level peripherals page to get me started.