Arduino GPS Geo-Fencing Alert System with SMS Notifications

1/*
2 * Geo-Fencing SMS Alarm System
3 * Hardware: Arduino Uno + SIM808 module
4 * SIM808 connected via SoftwareSerial: TX=10, RX=11
5 * Alert number: change ALERT_NUMBER below
6 */
7
8#include <SoftwareSerial.h>
9
10// ── Pins ──────────────────────────────────────────────
11#define SIM808_RX 10   // Arduino RX ← SIM808 TX
12#define SIM808_TX 11   // Arduino TX → SIM808 RX
13
14// ── Geo-fence config ──────────────────────────────────
15const double FENCE_LAT   = 30.9010;   // Centre latitude  (your location)
16const double FENCE_LON   = 75.8573;   // Centre longitude (your location)
17const double FENCE_RADIUS_M = 200.0;  // Radius in metres
18
19// ── SMS config ────────────────────────────────────────
20const char* ALERT_NUMBER = "+91XXXXXXXXXX";   // Recipient number
21
22// ── Timing ────────────────────────────────────────────
23const unsigned long GPS_POLL_MS   = 5000;   // Poll GPS every 5 s
24const unsigned long SMS_COOLDOWN  = 60000;  // Min 60 s between SMS bursts
25
26// ─────────────────────────────────────────────────────
27SoftwareSerial sim808(SIM808_RX, SIM808_TX);
28
29double  currentLat = 0, currentLon = 0;
30bool    gpsValid        = false;
31bool    wasInsideFence  = true;   // Assume inside at boot
32unsigned long lastSmsTime = 0;
33unsigned long lastPollTime = 0;
34
35// ── Haversine distance (metres) ───────────────────────
36double haversine(double lat1, double lon1, double lat2, double lon2) {
37  const double R = 6371000.0;
38  double dLat = radians(lat2 - lat1);
39  double dLon = radians(lon2 - lon1);
40  double a = sin(dLat / 2) * sin(dLat / 2)
41           + cos(radians(lat1)) * cos(radians(lat2))
42           * sin(dLon / 2) * sin(dLon / 2);
43  return R * 2.0 * atan2(sqrt(a), sqrt(1.0 - a));
44}
45
46// ── Parse $GPRMC NMEA sentence ────────────────────────
47bool parseGPRMC(const String& sentence) {
48  // $GPRMC,HHMMSS.ss,A,LLLL.LL,a,YYYYY.YY,a,x.x,x.x,DDMMYY,x.x,a*hh
49  if (!sentence.startsWith("$GPRMC")) return false;
50
51  int field = 0;
52  int start = 0;
53  char statusChar = 'V';
54  double rawLat = 0, rawLon = 0;
55  char latDir = 'N', lonDir = 'E';
56
57  for (int i = 0; i <= (int)sentence.length(); i++) {
58    char c = (i < (int)sentence.length()) ? sentence[i] : ',';
59    if (c == ',' || c == '*') {
60      String token = sentence.substring(start, i);
61      switch (field) {
62        case 2: statusChar = token.length() ? token[0] : 'V'; break;
63        case 3: rawLat = token.toDouble();  break;
64        case 4: latDir = token.length() ? token[0] : 'N'; break;
65        case 5: rawLon = token.toDouble();  break;
66        case 6: lonDir = token.length() ? token[0] : 'E'; break;
67      }
68      field++;
69      start = i + 1;
70    }
71  }
72
73  if (statusChar != 'A') return false;   // No valid fix
74
75  // Convert DDDMM.mmmm → decimal degrees
76  int latDeg = (int)(rawLat / 100);
77  double latMin = rawLat - latDeg * 100.0;
78  currentLat = latDeg + latMin / 60.0;
79  if (latDir == 'S') currentLat = -currentLat;
80
81  int lonDeg = (int)(rawLon / 100);
82  double lonMin = rawLon - lonDeg * 100.0;
83  currentLon = lonDeg + lonMin / 60.0;
84  if (lonDir == 'W') currentLon = -currentLon;
85
86  return true;
87}
88
89// ── Send AT command, wait for response ────────────────
90String sendAT(const String& cmd, unsigned int timeout = 2000) {
91  sim808.println(cmd);
92  String resp = "";
93  unsigned long t = millis();
94  while (millis() - t < timeout) {
95    while (sim808.available()) resp += (char)sim808.read();
96  }
97  Serial.println(">> " + cmd);
98  Serial.println("<< " + resp);
99  return resp;
100}
101
102// ── Send SMS ──────────────────────────────────────────
103void sendSMS(const String& message) {
104  sendAT("AT+CMGF=1");          // Text mode
105  sendAT(String("AT+CMGS=\"") + ALERT_NUMBER + "\"", 2000);
106  sim808.print(message);
107  sim808.write(26);             // Ctrl+Z to send
108  delay(5000);                  // Wait for modem to transmit
109  Serial.println("SMS sent: " + message);
110}
111
112// ── Initialise SIM808 ─────────────────────────────────
113void initSIM808() {
114  Serial.println("Initialising SIM808...");
115  delay(3000);
116
117  sendAT("AT");                 // Handshake
118  sendAT("AT+CPIN?");           // SIM ready?
119  sendAT("AT+CREG?");           // Network registration
120  sendAT("AT+CGPSPWR=1");       // GPS power on
121  sendAT("AT+CGPSRST=0");       // Reset GPS data
122  delay(2000);
123  Serial.println("SIM808 ready.");
124}
125
126// ── Request fresh GPS string from SIM808 ─────────────
127String getGPSString() {
128  // SIM808 GPS AT command — returns NMEA $GPRMC via UART
129  sendAT("AT+CGPSINF=0", 2000);   // GPS info mode 0 = RMC sentence
130  // Alternatively read raw NMEA if GPS UART is passed through:
131  String line = "";
132  unsigned long t = millis();
133  while (millis() - t < 3000) {
134    if (sim808.available()) {
135      char c = sim808.read();
136      if (c == '\n') {
137        if (line.startsWith("$GPRMC")) return line;
138        line = "";
139      } else if (c != '\r') {
140        line += c;
141      }
142    }
143  }
144  return "";
145}
146
147// ─────────────────────────────────────────────────────
148void setup() {
149  Serial.begin(9600);
150  sim808.begin(9600);
151  initSIM808();
152}
153
154void loop() {
155  unsigned long now = millis();
156
157  if (now - lastPollTime >= GPS_POLL_MS) {
158    lastPollTime = now;
159
160    String nmea = getGPSString();
161    gpsValid = parseGPRMC(nmea);
162
163    if (gpsValid) {
164      double dist = haversine(currentLat, currentLon, FENCE_LAT, FENCE_LON);
165
166      Serial.print("Lat: "); Serial.print(currentLat, 6);
167      Serial.print("  Lon: "); Serial.print(currentLon, 6);
168      Serial.print("  Dist: "); Serial.print(dist, 1); Serial.println(" m");
169
170      bool insideNow = (dist <= FENCE_RADIUS_M);
171
172      // Exited fence
173      if (wasInsideFence && !insideNow) {
174        if (now - lastSmsTime >= SMS_COOLDOWN) {
175          String msg = "ALERT: Device left geo-fence!\n";
176          msg += "Lat: "; msg += String(currentLat, 6);
177          msg += "\nLon: "; msg += String(currentLon, 6);
178          msg += "\nDist: "; msg += String(dist, 1); msg += " m";
179          sendSMS(msg);
180          lastSmsTime = now;
181        }
182      }
183
184      // Returned to fence (optional entry alert)
185      if (!wasInsideFence && insideNow) {
186        if (now - lastSmsTime >= SMS_COOLDOWN) {
187          sendSMS("INFO: Device returned inside geo-fence.");
188          lastSmsTime = now;
189        }
190      }
191
192      wasInsideFence = insideNow;
193
194    } else {
195      Serial.println("Waiting for GPS fix...");
196    }
197  }
198}