Interesting. I don't have a microphone, but it did detect my Rocksmith guitar cable as a mike. It almost worked, but didn't quite get the right tone - I'm assuming the custom cable isn't just a straight-out mike.

The needle was very stuttery, as opposed to other tuners which have a much higher frequency update. Is it always like this, or am I seeing perhaps an interaction effect with this non-standard mike?

Nice work, though.