Lesson 5: Calibrate Your Sensor

/*
  DIY KIT - Arduino Ultrasonic Distance & Parking Learning Kit
  Lesson 5 of 9: Calibrate Your Sensor

  WIRING: the sensor from Lesson 1 (TRIG pin 9, ECHO pin 10).
  The LEDs and buzzer can stay connected; this sketch does not use them.

  HOW TO USE IT
    1. Open the Serial Monitor at 9600 baud. Check the box at the bottom
       right is set to "New Line".
    2. Put a flat card at a ruler mark, for example 20 cm.
    3. Type 20 and press Enter. The UNO takes 10 readings and prints one row:
       ruler_cm, average_cm, error_cm, min_cm, max_cm, spread_cm, echoes
    4. Repeat at 10, 20, 30, 50, 75 and 100 cm. Copy the rows into a spreadsheet.
*/

const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

const int SAMPLES = 10;                        // readings per row
const unsigned long ECHO_TIMEOUT_US = 30000;
const int MIN_CM = 2;
const int MAX_CM = 400;

long typedNumber = 0;     // the number being typed, digit by digit

long readOnceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, ECHO_TIMEOUT_US);
  if (us == 0) return 0;
  long cm = us / 58;
  if (cm < MIN_CM || cm > MAX_CM) return 0;
  return cm;
}

// Take SAMPLES readings and print one spreadsheet row.
void measureAt(long rulerCm) {
  long total = 0;
  long lowest = 9999;
  long highest = 0;
  int echoes = 0;

  for (int i = 0; i < SAMPLES; i++) {
    long cm = readOnceCm();
    if (cm > 0) {
      total = total + cm;
      echoes = echoes + 1;
      if (cm < lowest) lowest = cm;
      if (cm > highest) highest = cm;
    }
    delay(60);
  }

  Serial.print(rulerCm);
  Serial.print(",");
  if (echoes == 0) {
    Serial.println("NA,NA,NA,NA,NA,0");
    return;
  }
  long average = total / echoes;
  Serial.print(average);            Serial.print(",");
  Serial.print(average - rulerCm);  Serial.print(",");   // error: + means it reads too far
  Serial.print(lowest);             Serial.print(",");
  Serial.print(highest);            Serial.print(",");
  Serial.print(highest - lowest);   Serial.print(",");   // spread: how much it wobbles
  Serial.println(echoes);
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println("Lesson 5: Calibrate Your Sensor");
  Serial.println("Put the card at a ruler mark, type the distance in cm and press Enter.");
  Serial.println("ruler_cm,average_cm,error_cm,min_cm,max_cm,spread_cm,echoes");
}

void loop() {
  while (Serial.available() > 0) {
    char c = Serial.read();
    if (c >= '0' && c <= '9') {
      typedNumber = typedNumber * 10 + (c - '0');   // build the number one digit at a time
    } else if (c == '\n' || c == '\r') {
      if (typedNumber > 0) measureAt(typedNumber);
      typedNumber = 0;
    }
  }
  delay(1);
}