Murat Süzen

Today, we take a detailed look at a powerful ESP32-based GPS tracker that uses both SIM800 (GPRS) and WiFi to send data, ensuring high resilience and flexibility. This article explores today’s deployment lessons, technical deep dive, and key implementation tips.

🛠 System Highlights

✅ ESP32 MCU with dual connectivity (WiFi + SIM800)
✅ NEO-6M GPS module to capture real-time positions
✅ LittleFS file system for local storage
✅ TinyGPS++ library for parsing NMEA data
✅ AT command system to control settings live

This setup logs GPS coordinates, stores them, and sends them over HTTP to a server — either via mobile network or local WiFi.

🌐 Dual Connectivity: Why Use Both?

Many IoT systems face environments where WiFi is unavailable or unreliable. By adding SIM800, your tracker can:

Fallback to mobile networks when WiFi fails.
Cover remote regions without WiFi infrastructure.
Switch between modes using AT+SETMODE=WIFI or AT+SETMODE=SIM800 without rebooting.

This makes the system field-deployable and self-recovering.

📍 GPS Data Flow

Step 1: Collect Data

  
while (gpsSerial.available()) {
    gps.encode(gpsSerial.read());
}

if (gps.location.isUpdated()) {
    float lat = gps.location.lat();
    float lng = gps.location.lng();
    float speed = gps.speed.kmph();
    String timestamp = getFormattedTime();
    String record = String(lat, 6) + "," + String(lng, 6) + "," + String(speed, 2) + "," + timestamp;
    appendToFile("/gpslog.txt", record);
}

✅ Logs are saved every update, ensuring no data is lost if the network is temporarily down.

📡 Sending Data via SIM800

Preparing SIM800

1️⃣ Activate bearer (APN):

  
sendATCommand("AT+SAPBR=1,1", 2000);

2️⃣ Setup HTTP:

  
sendATCommand("AT+HTTPINIT", 1000);
sendATCommand("AT+HTTPPARA=\"URL\",\"http://server/api\"", 1000);

3️⃣ Push data:

  
sendATCommand("AT+HTTPDATA=length,timeout", 1000);
sim800Serial.print(jsonPayload);
sendATCommand("AT+HTTPACTION=1", 10000);

4️⃣ Cleanup:

  
sendATCommand("AT+HTTPTERM", 1000);

✅ Debug tip: Use AT+CSQ to check signal; aim for strength >10.

📶 Sending Data via WiFi

  
if (client.connect(SERVICE_IP.c_str(), SERVICE_PORT.toInt())) {
    client.println("POST /api HTTP/1.1");
    client.println("Host: " + SERVICE_IP);
    client.println("Content-Type: application/json");
    client.print("Content-Length: ");
    client.println(json.length());
    client.println();
    client.println(json);
}

✅ Resilience tip: Use connection retries and check WiFi.status() regularly.

🔧 Dynamic AT Command Control

With the built-in AT command system, you can change settings live:

Command	Action
`AT+SETID=<ID>`	Update device ID
`AT+SETADDR=<IP:PORT>`	Change server address
`AT+SETMODE=WIFI`	Switch to WiFi mode
`AT+SETMODE=SIM800`	Switch to SIM800 mode
`AT+STARTGPS`	Enable GPS logging
`AT+STOPGPS`	Disable GPS logging

✅ Field tip: You can also pull commands from the server dynamically via /api/TelemetryData/NextCommand/{DEVICE_ID}.

🌍 Real-World Use Cases

Vehicle tracking in mixed rural/urban zones
Wildlife monitoring where WiFi is rare
Delivery fleet systems that need dual redundancy
Remote sensors pushing environmental data

✅ Summary

Today’s build showcases a flexible, powerful ESP32 GPS tracker that seamlessly switches between WiFi and SIM800 connections, ensuring robust field operation. With smart AT command integration and careful data handling, you can confidently deploy this system in real-world scenarios.

ESP32 GPS Tracker with SIM800 and WiFi Today’s Deep Dive