Build a GPS Tracker That Works Anywhere (No App!)

#include <SoftwareSerial.h>
#include <TinyGPS++.h>

// GPS Module connections
#define GPS_RX_PIN 4
#define GPS_TX_PIN 3

// SIM800L Module connections
#define SIM800L_RX_PIN 7
#define SIM800L_TX_PIN 8

// Create serial objects
SoftwareSerial gpsSerial(GPS_RX_PIN, GPS_TX_PIN);
SoftwareSerial sim800l(SIM800L_RX_PIN, SIM800L_TX_PIN);

// GPS object
TinyGPSPlus gps;

// Configuration
const float SAFE_ZONE_LAT = 14.5995;  // Replace with your safe zone latitude
const float SAFE_ZONE_LON = 120.9842; // Replace with your safe zone longitude
const float SAFE_ZONE_RADIUS = 0.001;  // Radius in degrees (approximately 100 meters)
const String PHONE_NUMBER = "+639123456789"; // Replace with your phone number

// State variables
unsigned long lastCheckTime = 0;
const unsigned long CHECK_INTERVAL = 30000; // Check every 30 seconds
bool isInSafeZone = true;
bool gpsReady = false;

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  gpsSerial.begin(9600);
  sim800l.begin(9600);
  
  Serial.println("GPS Tracker Initializing...");
  
  // Wait for SIM800L to be ready
  delay(2000);
  
  // Initialize SIM800L
  sim800l.println("AT");
  delay(1000);
  sim800l.println("AT+CMGF=1"); // Set SMS mode to text
  delay(1000);
  sim800l.println("AT+CNMI=2,2,0,0,0"); // Set SMS notification
  delay(1000);
  
  Serial.println("GPS Tracker Ready!");
  sendSMS("GPS Tracker initialized and ready.");
}

void loop() {
  // Read GPS data
  while (gpsSerial.available() > 0) {
    if (gps.encode(gpsSerial.read())) {
      if (gps.location.isValid()) {
        gpsReady = true;
      }
    }
  }
  
  // Check location every CHECK_INTERVAL
  if (millis() - lastCheckTime > CHECK_INTERVAL) {
    lastCheckTime = millis();
    
    if (gpsReady && gps.location.isValid()) {
      float currentLat = gps.location.lat();
      float currentLon = gps.location.lng();
      
      // Calculate distance from safe zone
      float distance = calculateDistance(
        SAFE_ZONE_LAT, SAFE_ZONE_LON,
        currentLat, currentLon
      );
      
      // Check if device is in safe zone
      bool currentlyInSafeZone = (distance <= SAFE_ZONE_RADIUS);
      
      // Send alert if device left safe zone
      if (isInSafeZone && !currentlyInSafeZone) {
        String message = "ALERT: Device left safe zone!\n";
        message += "Location: ";
        message += String(currentLat, 6);
        message += ", ";
        message += String(currentLon, 6);
        message += "\n";
        message += "Distance: ";
        message += String(distance * 111000, 2); // Convert to meters
        message += " meters";
        
        sendSMS(message);
        isInSafeZone = false;
      }
      
      // Update status when back in safe zone
      if (!isInSafeZone && currentlyInSafeZone) {
        sendSMS("Device returned to safe zone.");
        isInSafeZone = true;
      }
      
      // Debug output
      Serial.print("Lat: ");
      Serial.print(currentLat, 6);
      Serial.print(", Lon: ");
      Serial.print(currentLon, 6);
      Serial.print(", Distance: ");
      Serial.print(distance * 111000, 2);
      Serial.println(" meters");
    } else {
      Serial.println("Waiting for GPS signal...");
    }
  }
  
  // Handle incoming SMS
  if (sim800l.available()) {
    String response = sim800l.readString();
    Serial.println("SIM800L: " + response);
    
    // Check for location request SMS
    if (response.indexOf("LOCATION") != -1 || response.indexOf("location") != -1) {
      if (gpsReady && gps.location.isValid()) {
        String locationMsg = "Current Location:\n";
        locationMsg += "Lat: ";
        locationMsg += String(gps.location.lat(), 6);
        locationMsg += "\nLon: ";
        locationMsg += String(gps.location.lng(), 6);
        locationMsg += "\n";
        locationMsg += "https://www.google.com/maps?q=";
        locationMsg += String(gps.location.lat(), 6);
        locationMsg += ",";
        locationMsg += String(gps.location.lng(), 6);
        
        sendSMS(locationMsg);
      } else {
        sendSMS("GPS signal not available. Please wait...");
      }
    }
  }
}

// Function to calculate distance between two coordinates
float calculateDistance(float lat1, float lon1, float lat2, float lon2) {
  float dLat = (lat2 - lat1) * PI / 180.0;
  float dLon = (lon2 - lon1) * PI / 180.0;
  
  float a = sin(dLat / 2) * sin(dLat / 2) +
            cos(lat1 * PI / 180.0) * cos(lat2 * PI / 180.0) *
            sin(dLon / 2) * sin(dLon / 2);
  
  float c = 2 * atan2(sqrt(a), sqrt(1 - a));
  float distance = c; // Distance in degrees
  
  return distance;
}

// Function to send SMS
void sendSMS(String message) {
  sim800l.println("AT+CMGS="" + PHONE_NUMBER + """);
  delay(1000);
  sim800l.print(message);
  delay(100);
  sim800l.write(26); // Ctrl+Z to send
  delay(1000);
  
  Serial.println("SMS sent: " + message);
}