Question

Ok so I get this code to do the averaging : (written in C )

.
.
        int sum[3];
        int j;
        int avg;
      for(;;) //infinite loop
      {
       for(j=0;j<3;j++){
        i = ReadSensor(); // function that keeps saving sensor values as int i
        sum[j]=i;
        }
       avg=sum[0]+sum[1]+sum[2]+sum[3]; 
       printf("Sonar: %d \r \n", avg >> 2);
      }
.
.

Is this correct ? im shifting by 2 to divide by avg / 2^(2) which is 4
The problem is im expecting a value of about 15, however I get about 8–9 .. Im not sure why this is happening ?

Basically the sensor’s readings fluctuate between 15-17, I want to get an average instead of printing noise values. Is my code correct ? Then why do I get wrong outputs !?

Answer 1

The number of values read from sensor is required twice. First, to control the number of iterations of for loop. Second, as the divisor of sum. Introduce a variable (say, N) to capture that.

Also, the division by shifting does not sound right, because that restricts the number of readings from the sensor to power of two.

enum { N = 4 };

sum = 0;
for( j = 0; j < N; j++) {
   i = ReadSensor(); // function that keeps saving sensor values as int i
   sum += i;
}
avg = sum / N; 
printf( "Sonar average: %d\n", avg );