Confused by oscilloscope - square wave signal to RPM

[6v6gt]

@dovvvvv

unsigned long pulse = 0;

This should also be marked a volatile because it is updated in an ISR and read elsewhere, possibly asynchronously.

Since pulse is > 1 byte, you need to suspend interrupts, during the time you make a copy of it, in order to avoid reading it in a half updated state (non-atomic read operation).

The second part you have effectively done, however you are doing much more while interrupts are suspended than necessary.

EDIT

@dovvvvv

noInterrupts();
  // This would be where you get 'thisMedian'
  // from the median filter.
  thisMedian = medianFilter.AddValue (pulse);
  interrupts();

This would minimise the time interrupts are suspended:

noInterrupts();
unsigned long pulseCopy = pulse ;
interrupts();
  // This would be where you get 'thisMedian'
  // from the median filter.
  thisMedian = medianFilter.AddValue (pulseCopy);  // pulseCopy