I have a vehicle speed sensor (vss) that produces an ac sine wave whose frequency is directly related to the input speed of the shaft on the sensor and the maximum frequency would probably be 350 Hz. While the frequency is what is used to determine the speed, the peak to peak voltage also varies greatly from 2V peak to peak to about 60V. I want to use this signal to drive a microcontroller input. What type of signal conditioning circuit should I use to get the most usable range from the sensor? I was thinking a transistor based opto isolator but how should I drive the LED?