Refrigerator Door Sensor

Many older refrigerators have hinges that are worn and may prevent them from fully closing. To combat this issue, I designed an Arduino based distance measurement system to detected if the door was left open. It uses a HC-SR04 ultrasonic sensor mounted on the side of the fridge and a small plastic popup as an area to reflect the sound waves emitted by the ultrasonic sensor. 

#define DELAY 180           // Delay before buzzer activation (seconds)

#define DELAY_SHORT 10 // Delay before buzzer activation when the door is barely open (seconds)

#define OPEN_THR 10.8 // Distance for door to be detected as "open"

#define B_OPEN_THR 4// Distance for door to be detected as "barely open"

#define BUZZER 9  // Buzzer pin

#define TRIG 3       // Sensor TRIGGER pin

#define ECHO 2     // Sensor ECHO pin

#define POWER 4  // Pin used as power bus

#define SOUND_SPEED 0.034 // Speed of sound in cm/μs

float distanceCm; // Variable to store distance in cm

void setup() {

  Serial.begin(9600); // Initialize serial monitor for debugging

  // Initialize pins

  pinMode(TRIG, OUTPUT);

  pinMode(ECHO, INPUT);

  pinMode(BUZZER, OUTPUT);

  pinMode(POWER, OUTPUT); 

  digitalWrite(POWER, HIGH); // Pin 4 is being used as a power bus for easy mounting of the ultrasonic censor

}

void loop() {

  distanceCm = measDist(); // Update distance variable

  if (distanceCm > OPEN_THR) { // Check if the door is wide open

    Serial.println("Open"); // Send info to serial monitor for  debugging

    digitalWrite(LED_BUILTIN, HIGH); // Turn on builtin LED for debugging

    for (unsigned int i = 0; i <= DELAY; i++) { // Wait for 180 (DELAY variable) seconds

      distanceCm = measDist(); // Update distance variable

      if (!(distanceCm > OPEN_THR)) { // If door has been closed, cancel timer

        return;

      }

      delay(1000);

    }

    pulse(3000); // Activate buzzer @ 3000hz

  } else if (distanceCm < OPEN_THR && distanceCm > B_OPEN_THR) {  // Check if the door is barely open

    Serial.println("Barely open"); // Send info to serial monitor for  debugging

    digitalWrite(LED_BUILTIN, HIGH); // Turn on builtin LED for debugging

    for (unsigned int i = 0; i <= DELAY_SHORT; i++) { // Wait for 10 (DELAY_SHORT variable) seconds

      distanceCm = measDist(); // Update distance variable

      if (!(distanceCm < OPEN_THR && distanceCm > B_OPEN_THR)) // If door has been closed, cancel timer

        return;

      delay(1000);

    }

    pulse(4000); // Activate buzzer @ 4000hz

  } else {

    digitalWrite(LED_BUILTIN, LOW); // Turn off builtin LED when door is not open.

  }

  Serial.print("Distance (cm): "); // Print distance in cm for easy configuration of "open", "barely open" variables.

  Serial.println(distanceCm);

  delay(500); // Cycle time

}

void pulse(const unsigned int FREQ) {

  for (unsigned int i = 0; i < 3; i++) { // Activate buzzer 3 times for 500ms.

    tone(BUZZER, FREQ, 500); // Send signal to BUZZER PIN at FREQ for 500ms

    delay(1000);

  }

}

float measDist() { // Measures distance

  static long duration;

  digitalWrite(TRIG, LOW);

  delayMicroseconds(2);

  digitalWrite(TRIG, HIGH);

  delayMicroseconds(10);

  digitalWrite(TRIG, LOW);

  duration = pulseIn(ECHO, HIGH); // Measure how long it takes an emitted ultrasonic pulse to return

  return duration * SOUND_SPEED / 2;

  delay(20);

}