Building an ESP32 GPS Tracker with SIM800, WiFi, and AT Command Integration

In this article, we explore a robust ESP32-based GPS tracking system that integrates:
✅ SIM800 module (GPRS) for cellular internet
✅ WiFi for wireless local connectivity
✅ TinyGPS++ library to handle GPS data
✅ LittleFS for onboard file storage
✅ AT command interpreter to control behavior over serial or a remote service

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System Overview

The ESP32 runs firmware that does the following:

• Continuously reads GPS data (latitude, longitude, speed, time).
• Stores data points in a local log (/gpslog.txt).
• Every 10 seconds, sends the collected data to a remote telemetry service over the internet, using either SIM800 (GPRS) or WiFi.
• Listens for remote AT commands (via HTTP GET) or local serial AT commands to dynamically change settings.

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Internet Connection Modes

✅ SIM800 Mode:

• Initializes GPRS (AT+SAPBR) and sends HTTP requests with AT commands.
• Retrieves and runs remote commands via /api/TelemetryData/NextCommand/{DEVICE_ID}.
• Sends collected GPS telemetry via HTTP POST.

✅ WiFi Mode:

• Connects to a local WiFi network using configured SSID and password.
• Uses WiFiClient to connect to the service IP and port.
• Dynamically switches between WiFi or SIM800 via AT commands.

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GPS Logging

• Uses TinyGPS++ to read NMEA data from the GPS module.
• Captures: latitude, longitude, speed, and UTC timestamp.
• Logs each data point to LittleFS (/gpslog.txt).
• On every post interval (default 10s), reads the log file, builds a JSON array, and transmits it to the telemetry API.

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Dynamic Configuration with AT Commands

The system accepts AT commands over:

• Serial input (e.g., AT+SETID=NEWID).
• Remote service (via HTTP GET).

Supported commands:

• AT+SETID, AT+GETID: manage device ID.
• AT+SETADDR, AT+GETADDR: set or get the telemetry service IP and port.
• AT+SETMODE=WIFI or AT+SETMODE=SIM800: switch internet modes.
• AT+SETWIFI=SSID,PASSWORD: configure WiFi credentials.
• AT+STARTGPS, AT+STOPGPS: enable or disable GPS logging.
• AT+RESTART: restart the ESP32 device.
• AT+TESTPOST: perform a test POST to verify connectivity.

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Service Endpoint Example

By default, the firmware targets:

http://serviceaddr:port/api/TelemetryData

You can change this at runtime by sending:

AT+SETADDR=192.168.1.100:8080

or programmatically adjusting:

SERVICE_IP = "192.168.1.100";
SERVICE_PORT = "8080";
saveServiceAddress();

This flexibility allows you to redirect the device to development, test, or production servers without reflashing.

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Key Takeaways

• Dual internet mode (SIM800 + WiFi) increases resilience.
• Modular AT command system simplifies live reconfiguration.
• File system (LittleFS) ensures reliable buffering when the network is unavailable.
• TinyGPS++ integration makes GPS handling precise and efficient.

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How to Use

• Update the service address, SSID, or APN in your environment.
• Connect your GPS module (e.g., NEO-6M) to the defined pins.
• Deploy the firmware and start capturing real-world telemetry.