Posted on February 22, 2018 at 19:47Just measure the frequency?
Apply the digital analog of the window filter. The window filter has a phase delay, this is exactly what you need. You need two filters. The first will cut off high-frequency oscillations, the second will be used to control the direction of the phase. To do this, you need to take the data from the first filter and compare it with the output of the second filter.
With apparent simplicity, your measurements can not occur in real time. Therefore, the time stamp at the time of the phase change must be taken from the report number and the system time. Having a real phase transition time - you can calculate the frequency. For reliability, you can accumulate many reports, then the result will have increased accuracy.
Phase transition control takes precedence over the threshold detector - switching always occurs at the top of the wave. And so is the advantage over FFT - you need much less computing and memory.
The window filter works very simply. This is the sum of the reports divided by their number. You do not need to apply a filter to every cycle of the ADC; it's simpler: a new report is added to the sum and the old one is subtracted, the amount is divided by the number of reports, and the cycle repeats.
