I've been making enable differential input (and also gain enable) on Arduino ADC by add wiring_differential.c into arduino library. I try to recording sinewave with 2 V amplitude (generate from signal generator) without DC offset. It looks like this while i graph it on spreadshet,
Download library and sample from here: http://sekarlangit.com/wp-content/uploads/2013/02/AnalogDiff.tar.gz
. Else, download from attachment.
I wrote complete post about this differential input but may it goes wrong for the table (please correct me). Here: http://sekarlangit.com/arduino-differential-gain.php