ESP32 GPS Tracker

// ESP32 GPS Tracker - Advanced (ThingSpeak MQTT + geofencing)
#include <TinyGPS++.h>
#include <WiFi.h>
#include <PubSubClient.h>
#include <WebServer.h>
#include <Preferences.h>
#include <math.h>

TinyGPSPlus gps;
HardwareSerial gpsSerial(2);
WiFiClient wifiClient;
PubSubClient mqtt(wifiClient);
WebServer server(80);
Preferences prefs;

const char* SSID="YourSSID", *PASS="YourPass";
const char* TS_HOST="mqtt3.thingspeak.com";
const int   TS_PORT=1883;
const char* TS_USER="YourTSUser";
const char* TS_PASS="YourTSApiKey";
const char* TS_CLIENT="ESP32GPS";
// Channel write topic format: channels/<channelID>/publish
const char* TS_TOPIC="channels/YOUR_CHANNEL_ID/publish";

double geoLat, geoLon, geoRadius; // geofence centre and radius in km
bool inFence=true;
unsigned long lastPublish=0;

double haversineKm(double la1,double lo1,double la2,double lo2){
  double R=6371.0, dLa=(la2-la1)*DEG_TO_RAD, dLo=(lo2-lo1)*DEG_TO_RAD;
  double a=sin(dLa/2)*sin(dLa/2)+cos(la1*DEG_TO_RAD)*cos(la2*DEG_TO_RAD)*sin(dLo/2)*sin(dLo/2);
  return R*2*atan2(sqrt(a),sqrt(1-a));
}

void publishTS(){
  char payload[128];
  snprintf(payload,sizeof(payload),
    "field1=%.6f&field2=%.6f&field3=%.1f&field4=%d",
    gps.location.lat(), gps.location.lng(),
    gps.speed.kmph(), (int)gps.satellites.value());
  mqtt.publish(TS_TOPIC, payload);
}

void checkGeofence(){
  double dist=haversineKm(geoLat,geoLon,gps.location.lat(),gps.location.lng());
  bool inside=(dist<=geoRadius);
  if(inFence && !inside){
    digitalWrite(4,HIGH); delay(200); digitalWrite(4,LOW);
    mqtt.publish("gps/alert","GEOFENCE_BREACH");
  }
  inFence=inside;
}

void setup(){
  Serial.begin(115200);
  gpsSerial.begin(9600,SERIAL_8N1,16,17);
  pinMode(4,OUTPUT);
  WiFi.begin(SSID,PASS);
  while(WiFi.status()!=WL_CONNECTED) delay(500);

  prefs.begin("geo",true);
  geoLat=prefs.getDouble("lat",0.0);
  geoLon=prefs.getDouble("lon",0.0);
  geoRadius=prefs.getDouble("r",0.5);
  prefs.end();

  mqtt.setServer(TS_HOST,TS_PORT);
  server.on("/",[](){
    String body="<h2>GPS Tracker</h2>";
    body+="<p>Lat: "+String(gps.location.lat(),6)+"</p>";
    body+="<p>Lon: "+String(gps.location.lng(),6)+"</p>";
    body+="<p><a href="https://maps.google.com/?q="+
          String(gps.location.lat(),6)+","+String(gps.location.lng(),6)+
          "">Open in Google Maps</a></p>";
    server.send(200,"text/html",body);
  });
  server.begin();
}

void loop(){
  while(gpsSerial.available()) gps.encode(gpsSerial.read());
  server.handleClient();

  if(!mqtt.connected()){
    mqtt.connect(TS_CLIENT,TS_USER,TS_PASS);
  }
  mqtt.loop();

  if(gps.location.isValid() && millis()-lastPublish>30000){
    publishTS();
    checkGeofence();
    lastPublish=millis();
  }
}