MarkT:
IC1, the one on the right has no feedback network and there is no DC bias to pin 3 (non-inverting input). Both of those are
show-stoppers.
That's actually part of the design. I was looking up op amps on wikipedia when I stumbled across the zero level detector. When everything is cooperating, this circuit can generate periodic pulses with the same frequenncy as the input signal's fundamental frequency. I don't actually know how it works, only that that's what it is doing. I'm building a guitar tuner.
retrolefty:
Well there won't be a difference if you run a wire from an arduino ground pin to your circuit's ground, as you should. But as you didn't show your wiring to the arduino I won't assume you did. 741s are very old (for decades now) that are not known for their quite behaviour and should never be used these days of much better opamps at same or cheaper prices.
The arduino is not connected. I'm not quite sure how or where I should plug it in. Originally, I was trying to build a single-supply op amp powered by the arduino, but that wasn't going anywhere fast.
I'm using the 741 because that's what I happen to have lying around. I have a 071's, if you think those would work better.