When UK Prime Minister David Cameron gave a speech at CeBIT this year, what examples did he use to highlight tech innovation in Britain? Yes, ARM andImagination were on his list, but he also referred to the tiny, Linux-based computer called Raspberry Pi, which has now sold over 2.5 million units. In a timely fashion, the Pi's makers, element 14, have just announced a new $33,Wolfson-powered audio card that should give the device a broader range of functions.