Tracker Diy

Building a Basic GPS Logger

The usual approach is getting an ESP32, a GPS module like the NEO-6M or NEO-8M, and an SD card module. Wire the GPS TX pin to an ESP32 UART, connect the SD module to SPI, and run everything off a LiPo battery. The code side is straightforward — read NMEA sentences from the serial port, parse out latitude and longitude, and write them to a CSV file on the SD card at a set interval. Most people use TinyGPS++ for parsing. It handles the heavy lifting of extracting coordinates from the raw GPGGA and GPRMC sentences. I ran into a specific issue with a project a while back where the GPS would log positions correctly during movement but the timestamps were drifting by several seconds each hour. The problem wasn't the GPS module itself — it was the ESP32's internal RTC losing time when the main power cycled. The workaround was simple but easy to miss: enable the ULP coprocessor to keep the RTC alive on battery backup, and call RTC.attachDeepSleepPowerOn() in your setup. After that, timestamps stayed accurate even after deep sleep cycles.

Tracker Diy Hardware Choices

The ESP32 is overkill if you just need static waypoint logging. For something cheaper and lower power, an Arduino Pro Mini with a separate GPS module works fine, but you lose the ability to do cellular telemetry later without significant rewiring. The NEO-8M module is worth the extra money over the NEO-6M — it acquires cold start in about 26 seconds versus 35+, and the updated firmware supports more constellations (GPS, GLONASS, BeiDou) simultaneously. Single-system receivers often struggle in urban canyon environments and will drop fixes entirely. Power consumption is where these projects usually fail. A bare ESP32 doing nothing draws roughly 80mA. With GPS and SD active, you're looking at 150-200mA. A standard 2000mAh LiPo gives you maybe 8-10 hours of continuous logging. If you're tracking something over days or weeks, you need to implement duty cycling — wake the GPS, record a fix, sleep for 30-60 seconds, repeat. This drops average current to around 30mA and extends runtime to roughly a day on the same battery. The tradeoff is that fast-moving subjects will have gaps in the trail data, though interpolation between points usually makes the route readable.

Cellular Telemetry vs. Local Logging

The bigger question is whether you actually need live tracking or just logging. Live tracking requires a cellular modem — an ESP32 with an A6 or SIM800L module adds complexity around power spikes (these modems draw 2A bursts during GSM registration), SIM management, and ongoing data costs. For most DIY applications, local SD logging and then downloading the data later is completely adequate and avoids the whole category of problems that come with cellular modules. If you do go the cellular route, don't build your own protocol. Use something like MQTT with QoS 1, or simpler yet, just POST JSON payloads to a webhook endpoint you control. The AT command interface on these modules is unreliable — you'll spend more time debugging modem handshakes than actually building useful features. Libraries like TinyGSM abstract most of that away, but they don't solve the fundamental issue that cellular networks are unpredictable in rural areas and these cheap modules have modest radios.

Common Mistakes

Voltage levels — the NEO-6M/8M GPS module outputs 3.3V on its TX pin, which the ESP32 accepts fine. But many SD card modules have a built-in level shifter that outputs 5V on MISO. Plug that directly into the ESP32's MOSI pin and you may corrupt the SPI bus or damage the pin. Use a proper logic level converter or buy an SD module that's explicitly 3.3V compatible. Antenna placement — the GPS antenna needs line of sight to the sky. Glue it to the outside of whatever enclosure you're using. Routing a 5cm dupont wire from an internal antenna through a metal box will kill your fix quality almost entirely. Similarly, keep the SD card module and cellular modem physically separated from the GPS antenna by at least 5cm — their switching noise will raise the noise floor and reduce sensitivity. Baud rate mismatches — most GPS modules default to 9600 baud, but some ship at 115200. If your parser isn't getting any output, check the actual baud rate with a serial monitor before assuming the code is wrong. You can also reconfigure the module's baud rate using UBX or NMEA factory commands, but you need to know which command set the module responds to, and that varies by manufacturer even within the same chip family.

Software Stack

For the logger side, I'd skip the heavy frameworks. A simple loop that checks the GPS fix status, reads a line from Serial1, runs it through TinyGPS++'s feed() method, and when a complete fix is available writes a timestamped CSV line to the SD card is all you need. Something like 40 lines of code total. More complex projects tend to accumulate unnecessary abstractions that make debugging harder when something goes wrong in the field. For visualizing the logged data, import the CSV into Google Earth as a KML file or use GPSVisualizer's online tool. Both handle large datasets reasonably well and don't require any special software installation. If you're dealing with thousands of points, split the file into chunks first — Google Earth starts choking around 10,000 placemarks. The whole Tracker Diy approach comes down to understanding what you actually need to track, how long it needs to last, and whether live telemetry is worth the added complexity. Most people overengineer the first version and never finish the project because the power budget or code complexity becomes unmanageable. Start with just logging to SD, verify it works for a full day, then add features if you actually need them.