A median filter is a type of FIR filter which typically takes an odd number of inputs (e.g. 5 or more usually more) and sorts them by value. The filtered output is the median value (the middle value). A median filter can be very effective at removing noise spikes.

Example Code

Start New Filter Sequence

	#define MEDIAN_FILTER_NO_OF_READINGS			512
	WORD count;
	static WORD filter_current_count;
	static WORD filter_buffer[MEDIAN_FILTER_NO_OF_READINGS];

	//START NEW FILTER SEQUENCE
	filter_current_count = 0;
	for (count = 0; count < MEDIAN_FILTER_NO_OF_READINGS; count++)
		filter_buffer[count] = 0;

Add Next Reading

	//ADD NEXT READING
	//w_temp is the new reading value to add
	//Move through the buffer from the last current entry and add this reading in its correct value ordered position
	for (count = filter_current_count; count <= filter_current_count; count--)
	{
		if (count > 0)
		{
			if (filter_buffer[(count - 1)] < w_temp)
			{
				filter_buffer[count] =  w_temp;
				break;
			}
			filter_buffer[count] = filter_buffer[(count - 1)];
		}
		else
		{
			filter_buffer[count] =  w_temp;			//This is a new lowest value to add at the bottom of the buffer
			break;
		}
	}
	filter_current_count++;

Get the Median Result

	//GET MEDIAN RESULT
	value_to_use = filter_buffer[(MEDIAN_FILTER_NO_OF_READINGS / 2)]