LilyGO GPS Tracker

A tiny GPS tracking app for the LilyGO T-SIM7600 board

Tested on the T-SIM7600E. May work on other LTE+GPS LilyGO boards.

The position is transmitted every minute to a server via UDP. The transmission is encrypted using AES-256-CTR and authenticated with HMAC-SHA256. There is only an uplink connection: the server never communicates with the LilyGO board (for now).

Setup

T-SIM7600E board

Dependencies to install in the Arduino IDE:

• libmbedtls
• TinyGsmClient

In the LilyGO project file, add the IP address of your server. Destination port can be changed if necessary:

#define SERVER_ADDR "XX.XX.XX.XX"
#define SERVER_PORT 55100

You must generate the AES key and HMAC secret yourself. Execute the following command twice, then insert the hexadecimal string into the Node.js server and as a C-style array in the LilyGO source project. Keys must be identical on both sides.

openssl rand -hex 32 | tee >(sed 's/../0x&, /g' | sed 's/, $/};/;s/^/{/' | sed '1s/^/\r\n/')

Add the keys here in the LilyGO project:

unsigned char keyAES[32] = { /* YOUR AES256 KEY*/ };
const unsigned char keyHMAC[32] = { /*YOUR HMAC SECRET*/ };

Add the keys here in the Node.js server:

const AESKey = Buffer.from('YOUR AES256 KEY', 'hex')
const HMACKey = Buffer.from('YOUR HMAC SECRET', 'hex')

For now, a static key is generated. The security is sufficient for the purpose and the amount of data that will be transmitted.

If Node.js server is running on a VPS (with a dedicated IP) inside a container (like LXC) and has a local IP, you need to forward packets:

sysctl -w net.ipv4.ip_forward=1
iptables -I INPUT 1 -i eno1 -p udp -m state --state NEW,ESTABLISHED -m udp --dport 55100 -j ACCEPT
iptables -t nat -A PREROUTING -i eno1 -p udp --dport 55100 -j DNAT --to-destination XX.XX.XX.XX:55100

Node.js server needs express web framework to work:

npm install express

Webpage is available here: http://XX.XX.XX.XX:3000/

Run the project

UDP packets are arriving after a few minutes. All packets are encrypted:

Your postion on the map:

Currently, there’s a basic auto-refresh every 75 seconds. Real-time positioning will be available in a future release.

What's next?

• Real-time positioning via WebSocket
• Limit data transmission only when tracker is moving
• Use esp32/modem sleep function to conserve battery

Changelog

• 2025-10-02

  • Fix encryption issue: include IV in HMAC calculation
  • Improve timing accuracy of pause between GPS acquisitions

• 2025-09-28

  • Initial release