Arduino code techniques

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Revision as of 13:34, 11 November 2014 by Alexanderg (Talk | contribs) (Low pass filter)

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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.

Integration

position += speed * dt; angle += gyro * dt;


Low pass filter

  • Problem: you have multiple ADC measurements (battery, ultrasonic etc.) that can quickly change. What value is the 'smooth value' (low-pass filter)? The goal of the low-pass filter is to only let through long-term changes, filtering out short-term fluctuations.
  • 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 lower, 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 = 0.1; // how much your values are 'smoothed'
void loop(){   
  value = (1.0-weight) * value   +   weight * analogRead(A0);   // low-pass values
  Serial.println(value); // print value
}

The time it takes to reach the full value depends on both the filter constants (0.9 and 0.1 in the example) and the sample rate of the loop (dt).


High pass filter

It allows short-duration signals to pass through while filtering out signals that are steady over time. This can be used to cancel out drift.

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