Read AC signal frequency of 2-100Hz at 80mV to 12V with Arduino
The diagram is sort of high-level concept- it does mention the use of a comparator, which will work, rather than a ST inverter, which will not. Even if you biased it to the (rather variable) center point of the inverter, the hysteresis is too large. 

Below is an appropriate circuit. R4 and the Schottky diodes D1/D2 clamp the input to about +/- a few hundred mV. C1 and R11 are the low pass filter. R10 is the pullup required by most comparators such as the LM393 shown. R1/R2 create a bit of hysteresis. R9 biases the input up by about half the hysteresis (since the hysteresis is one-sided due to the 0/5V output of the comparator rather than a symmetric output about ground. 







simulate this circuit &ndash; Schematic created using CircuitLab

Note: Not included in this circuit is any consideration of lightning protection, as it's outside the scope of the signal processing issues. You can find more information at this link, for example. It should not be neglected for a real installation.