Building a DIY GPS Tracker

Built a real-time GPS tracker with a SIM800L GSM module and a NEO-6M GPS module. The device sends its location over SMS every 5 minutes.

The SIM800L is power-hungry during GSM transmission — up to 2A peak. This means your power supply must handle the spike or the module resets during transmission. I use a 2200uF cap bank on the SIM800L supply rail specifically to absorb this surge.

Software architecture: the GPS and GSM modules both use UART. I ran them on separate hardware UARTs on an STM32F103 (Blue Pill). Parsing NMEA sentences from the NEO-6M uses a simple state machine — I only care about GPRMC sentences which contain lat, lon, speed, and course. The SIM800L AT command protocol requires careful flow control: always wait for the expected response before sending the next command, with a timeout and retry logic for each step.