Making Sense of Sensor Data: A Beginner's Processing Tutorial

Putting It All Together: A Line-Following Example

Let's combine what we've learned into a more complete (though still simplified) example for a line-following robot using an array of IR reflectance sensors. Each sensor gives a reading, and we want to determine if the robot is centered on a line, drifting left, or drifting right.

// Simplified Line Following Logic with Averaging Filter

const int LEFT_SENSOR_PIN = A1;
const int CENTER_SENSOR_PIN = A2;
const int RIGHT_SENSOR_PIN = A3;

const int NUM_READINGS = 5; // For averaging filter
int leftReadings[NUM_READINGS];
int centerReadings[NUM_READINGS];
int rightReadings[NUM_READINGS];
int leftIndex = 0, centerIndex = 0, rightIndex = 0;
long leftTotal = 0, centerTotal = 0, rightTotal = 0;

const int LINE_THRESHOLD = 400; // Assume values below this are 'black line'

void setup() {
  Serial.begin(9600);
  for (int i = 0; i < NUM_READINGS; i++) {
    leftReadings[i] = 0; centerReadings[i] = 0; rightReadings[i] = 0;
  }
}

// Function to get filtered sensor value
int getFilteredValue(int pin, int readings[], int& index, long& total) {
  total -= readings[index];
  readings[index] = analogRead(pin);
  total += readings[index];
  index = (index + 1) % NUM_READINGS;
  return total / NUM_READINGS;
}

void loop() {
  int filteredLeft = getFilteredValue(LEFT_SENSOR_PIN, leftReadings, leftIndex, leftTotal);
  int filteredCenter = getFilteredValue(CENTER_SENSOR_PIN, centerReadings, centerIndex, centerTotal);
  int filteredRight = getFilteredValue(RIGHT_SENSOR_PIN, rightReadings, rightIndex, rightTotal);

  bool leftOnLine = (filteredLeft < LINE_THRESHOLD);
  bool centerOnLine = (filteredCenter < LINE_THRESHOLD);
  bool rightOnLine = (filteredRight < LINE_THRESHOLD);

  Serial.print("L: "); Serial.print(filteredLeft); Serial.print(" ("); Serial.print(leftOnLine ? "BLACK" : "WHITE"); Serial.print(") | ");
  Serial.print("C: "); Serial.print(filteredCenter); Serial.print(" ("); Serial.print(centerOnLine ? "BLACK" : "WHITE"); Serial.print(") | ");
  Serial.print("R: "); Serial.print(filteredRight); Serial.print(" ("); Serial.print(rightOnLine ? "BLACK" : "WHITE"); Serial.println(")");

  if (centerOnLine) {
    Serial.println("Robot is centered. Go straight!");
    // moveMotorsStraight();
  } else if (leftOnLine) {
    Serial.println("Robot drifted right. Turn left slightly!");
    // turnMotorsLeft();
  } else if (rightOnLine) {
    Serial.println("Robot drifted left. Turn right slightly!");
    // turnMotorsRight();
  } else {
    Serial.println("Lost line! Search for line.");
    // searchForLine();
  }

  delay(50);
}

This example demonstrates how filtering (using the `getFilteredValue` function) and thresholding (`LINE_THRESHOLD`) work together to provide actionable intelligence for the robot. Remember that proper sensor calibration is key to setting effective thresholds.