Few questions about design

[sselbe]

Few questions about design

[olewolf]

The diodes are there to protect the input of the Arduino but they aren't really necessary as long as the op-amp is powered with the same voltage as the Arduino can tolerate on its analog inputs. So, you'll probably be safe omitting the diodes.

I assume you're referring to capacitor C11. This is a decoupling capacitor that one should always place very close to the power supply pins on any IC. It helps reduce electrical noise.

It would probably be relatively straight-forward to design a multiplexer between three geophone inputs and thus have just one amplifier on one pin, but personally I'd just build three amplifiers and connect them to three pins. (Actually, I believe the Arduino multiplexes the analog inputs onto a single ADC internally.)

[sselbe]

Great, thanks @olewolf. I actually did just build the three amps and will just connect to other analog inputs. I appreciate all the great documentation on this project.