Choosing single cycle from Sinewave plot

Hi fellas,

I'm not sure how to do this and hope you can enlighten me. I have a CSV file with 2500r x 3c worth of data and when plotted a sinewave is obtained.

My question is, how do I choose a cycle from this dataset? Note that the data points don't actually cross y=0. The uncertainty I'm having is how exactly do I make MATLAB find the near-zero points of a single cycle's start and end point? Also, taking in mind that there will be another near-zero point at the half-cycle point.

I could do this visually but I have 300 datasets and need to make a script for this.

Thanks guys!

[dpb]

Is the process stationary? If so, simply remove mean and look for

diff(y)==+/-1

The two Positive or two Negative neighors are the extent of a cycle.

If it isn't stationary, detrend as well. If signal is noisy, some additional testing is likely required.