Convert sine wave from NRG Anemometer to square wave
Sounds like a comparator would be a good option. AC couple the signal from the anemometer into a comparator. Add a large voltage divider after the cap to get a good reference level. Make sure the voltage divider and cap will give you a show enough timestamp - you may need to use a rather large capacitor. Then use a comparator circuit that has a few 10s of mv of hysteresis. Place a couple of diodes between the comparator input and the voltage for protection.