how to read sine wave response from sensor

[ronsimpson]

i know that with the instruction "count" its posible , but due to kind of wave it is , i dont know how to read the sensor.

the sensor its nrg 40 anemometer :

low level AC sine wave, frequency linearly proportional to windspeed , from 0 to 125 hz.

its posible to read with this sensor without any auxiliar circuit¿? or its needed to read?

http://www.tande.com.tw/ins-img-anem...ecs-nrg40h.pdf
I think it needs a 250 ohm resistor to +5 volts. Its output is square wave.
It looks like the MPH=about 1.7 x frequency.
If you counted for 1.7 seconds then the value = MPH.