Help with FreqMeasure for Turbo Shaft Speed

[joepasquariello]

If you confirm it's a hardware issue, a software work-around, at least temporarily, might be a "glitch filter" like this:

period = fm.read();
speed_temp = 60 * fm.countToFrequency(period);
// use this measurement only if implied acceleration is reasonable
if (fabs(speed_temp - speed_prev) < accel_max) {
  update longer-term average (or whatever)
  speed = speed_temp;
  speed_prev = speed;
}