<r>If you are interested in radio applications then you might wish to have a look at this: <URL url="http://sdr.osmocom.org/trac/wiki/rtl-sdr">http://sdr.osmocom.org/trac/wiki/rtl-sdr</URL><br/> <br/> I very cheap USB dvb-t receiver that can be used as a software defined radio with GNU radio.<br/> <...

<r>I know it isnt very DIY buy you might want to take a look at the quake catcher network at stanford <URL url="http://qcn.stanford.edu/">http://qcn.stanford.edu/</URL> their sensor costs $49 *However!* from what i have seen it isnt currently supported under linux, a quick search suggests it appears...