Arduino code techniques

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This page shows example code, common code techniques etc. that can be useful for your own programming experiments with the Arduino.

Low pass filter

  • Problem: you have multiple ADC measurements (battery, ultrasonic etc.) that can quickly change. What value is the 'smooth value'?
  • Solution: This code will apply a 'low-pass' filter to your values. A 'weight' constant specifies the cut-off frequency, so how much your values are 'smoothed'. If the weight is higher, the cutt-off frequency is lower (so more is filtered out), however the more slowly the system adapts to the last measurements.
float value = 0.0; 
float weight = 0.9; // how much your values are 'smoothed'
void loop(){   
  value = (1.0-weight) * value   +   weight * analogRead(A0);   // low-pass values
  Serial.println(value); // print value
}


Mean filter

  • Problem: you have multiple ADC measurements (battery, ultrasonic etc.) that can contain outliers. What value is the 'most seen value'?
  • Solution: This code will sort and choose the center value.
  • Example measurements: 32,7,7,1,6,8,7,9,23,7,8,9,7
  • Sorted: 1,6,7,7,7,7,7,8,8,9,9,23,32
  • Returned: 7 (center value)
unsigned int ADCmedian(int pin, int count) {
  int values[count], last;
  uint8_t j, i = 0;
  values[0] = 0;
  while (i < count) {
    last = analogRead(pin);
    if (i > 0) {       
       for (j = i; j > 0 && values[j - 1] < last; j--) // Insertion sort loop.
   values[j] = values[j - 1]; // Shift ping array to correct position for sort insertion.
    } else j = 0;              // First ping is starting point for sort.
    values[j] = last;              // Add last ping to array in sorted position.
    i++;                       // Move to next ping.    
    if (i < count) delay(1); 
   }
   return (values[count/2]); // Return the median.
}


Further links