Tsunami Detection Alarm

#include <Arduino.h>


// Forward declarations
float readDistanceCm();
float medianOfThreeDistances();
void setBuzzer(bool enabled);

const int VIBRATION_PIN = 32;
const int TRIG_PIN = 25;
const int ECHO_PIN = 33;
const int YELLOW_LED_PIN = 26;
const int BUZZER_PIN = 27;

const unsigned long SAMPLE_INTERVAL_MS = 1000;
const unsigned long ALARM_DURATION_MS = 10000;
const float CHANGE_THRESHOLD_CM = 3.0f;
const int BUZZER_CHANNEL = 0;
const int BUZZER_FREQUENCY_HZ = 2000;

float previousDistanceCm = -1.0f;
unsigned long lastSampleMs = 0;
unsigned long alarmUntilMs = 0;

float readDistanceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(3);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  unsigned long duration = pulseIn(ECHO_PIN, HIGH, 30000);
  if (duration == 0) {
    return -1.0f;
  }

  float distance = (duration * 0.0343f) / 2.0f;
  if (distance < 2.0f || distance > 400.0f) {
    return -1.0f;
  }
  return distance;
}

float medianOfThreeDistances() {
  float readings[3];
  int validCount = 0;

  for (int i = 0; i < 3; i++) {
    float reading = readDistanceCm();
    if (reading > 0.0f) {
      readings[validCount++] = reading;
    }
    delay(60);
  }

  if (validCount == 0) {
    return -1.0f;
  }
  if (validCount == 1) {
    return readings[0];
  }
  if (validCount == 2) {
    return (readings[0] + readings[1]) / 2.0f;
  }

  if (readings[0] > readings[1]) {
    float temp = readings[0];
    readings[0] = readings[1];
    readings[1] = temp;
  }
  if (readings[1] > readings[2]) {
    float temp = readings[1];
    readings[1] = readings[2];
    readings[2] = temp;
  }
  if (readings[0] > readings[1]) {
    float temp = readings[0];
    readings[0] = readings[1];
    readings[1] = temp;
  }
  return readings[1];
}

void setBuzzer(bool enabled) {
  if (enabled) {
    ledcWriteTone(BUZZER_CHANNEL, BUZZER_FREQUENCY_HZ);
  } else {
    ledcWriteTone(BUZZER_CHANNEL, 0);
  }
}

void setup() {
  Serial.begin(115200);

  pinMode(VIBRATION_PIN, INPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(YELLOW_LED_PIN, OUTPUT);
  digitalWrite(YELLOW_LED_PIN, LOW);

  ledcSetup(BUZZER_CHANNEL, BUZZER_FREQUENCY_HZ, 8);
  ledcAttachPin(BUZZER_PIN, BUZZER_CHANNEL);
  setBuzzer(false);

  Serial.println("Tsunami detector started. Waiting for first water-level reading.");
}

void loop() {
  // Most SW-420 modules output HIGH while the sensor is vibrating.
  bool vibrationDetected = digitalRead(VIBRATION_PIN) == HIGH;
  digitalWrite(YELLOW_LED_PIN, vibrationDetected ? HIGH : LOW);

  unsigned long now = millis();
  if (now - lastSampleMs >= SAMPLE_INTERVAL_MS) {
    lastSampleMs = now;
    float currentDistanceCm = medianOfThreeDistances();

    if (currentDistanceCm > 0.0f) {
      if (previousDistanceCm > 0.0f) {
        float changeCm = fabsf(currentDistanceCm - previousDistanceCm);
        Serial.print("Water surface distance: ");
        Serial.print(currentDistanceCm, 1);
        Serial.print(" cm; change: ");
        Serial.print(changeCm, 1);
        Serial.println(" cm");

        if (changeCm >= CHANGE_THRESHOLD_CM) {
          alarmUntilMs = now + ALARM_DURATION_MS;
          Serial.println("Water-level alarm: 3 cm or greater change detected.");
        }
      } else {
        Serial.print("Reference water-surface distance: ");
        Serial.print(currentDistanceCm, 1);
        Serial.println(" cm");
      }
      previousDistanceCm = currentDistanceCm;
    } else {
      Serial.println("No usable ultrasonic reading; check that the sensor faces the water.");
    }
  }

  bool alarmActive = (long)(alarmUntilMs - now) > 0;
  setBuzzer(alarmActive);
}