Code

FIR 2kHz Bandstop Comb Filter

Ron April 1, 2011 Coded in C for the TI C67x

This will filter out a 2kHz that may be corrupting your input signal.

#define COMB_FILTER_ORDER		3	// Filter Order, i.e., M
#define DELAY_ARRAY_SIZE		9	// Number of (delayed) input samples to store

int   filtersum;			 	// Sum-of-products accumulator for calculating the filter output value
int   delay[DELAY_ARRAY_SIZE];			// Array for storing (delayed) input samples

static int gain1 = 1;				
static int gain2 = 4;				

interrupt void isr()	 			//Interrupt service routine
{							
     short i; 		 			// Loop counter	 
     delay[0] = get_sample() / gain1;		// Read filter input sample from ADC  and scale the sample		
     filtersum = delay[0];			// Initialize the accumulator
     for (i = COMB_FILTER_ORDER; i > 0; i--)
     {
     	filtersum += delay[i];			// Accumulate array elements
	delay[i] = delay[i-1];			// Shift delay elements by one sample
     }
     filtersum *= gain2;			// Scale the sum-of-products
     send_output(filtersum);			// write filter output sample to DAC
     return;					// interrupt servicing complete
}

void main()
{
     short i;	// loop counter
     for (i=0; i< DELAY_ARRAY_SIZE; i++)	// Initialize delay elements with 0
     { 
          delay[i] = 0;
     }
     init_all();                  		// global initialization
     while(1);    		   		// infinite loop
						// do nothing except wait for the interrupt	 
}

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