u/nolilab

Hi everyone,

I designed a small open-source LoRa GPS tracker over the past couple of years and recently recorded a complete build and teardown video. I'm posting it here because this community has a lot of RF and embedded experience, and I'd really appreciate technical feedback.

Video:
https://www.youtube.com/watch?v=A1PXd6E6GVs

Before anyone asks: this is not a Meshtastic device.

It uses LoRa point-to-point communication between a tracker and a receiver rather than a mesh network. I considered making it Meshtastic-compatible during development, but for the specific use case I was targeting—recovering a lost drone, dog, vehicle, or equipment—I decided to optimize for battery life, simplicity, and deterministic communication instead of maintaining a mesh stack.

The tracker hardware is based on:

• STM32WLE5JC (LoRa SoC)
• PA1010D (MediaTek MT3333 GNSS receiver)
• 200 mAh rechargeable Li-ion battery
• Approximately 15 g fully assembled

Power consumption:

• Sleep: approximately 10 µA
• GPS active: approximately 36 mA
• MCU standby current: approximately 2.1 µA
• Packet transmission interval is user configurable.

The receiver is ESP32-based and forwards received GPS coordinates to a smartphone over Bluetooth.

Everything is open source, including the hardware and firmware, because I'd rather people learn from the design than keep it closed.

I'd especially appreciate feedback on:

• Overall hardware design
• Antenna implementation
• Anything you would have done differently with the STM32WL architecture
• Battery optimization ideas
• Whether there is genuine interest in a Meshtastic-compatible variant, or whether a dedicated P2P/LoRaWAN tracker makes more sense for this type of application

I don't mind criticism—in fact, I'd appreciate it. If you spot something questionable in the RF design, antenna matching, or firmware architecture, please point it out.

Do you think I need to implement meshtastic firmware too?

Lora GPS Tracker

One of the hardest parts of building my LoRa GPS tracker wasn't the RF design or even the firmware.

It was battery life.

When people ask how a tiny GPS tracker can last close to a year on a single charge, they usually expect some secret hardware trick.

There isn't one.

It's mostly about avoiding unnecessary work.

Here are a few of the biggest lessons I learned:

• Sleeping is everything. Every microamp matters when your goal is measured in months instead of days. Most of the time, the MCU is doing absolutely nothing—and that's exactly how it should be.

• GPS is expensive. Keeping the receiver running continuously drains power quickly. Deciding when to acquire a fix turned out to be just as important as getting the fix itself.

• Radio airtime matters. Transmitting every second sounds nice until you look at the battery graph. Simply increasing the reporting interval can extend runtime dramatically.

• Every wake-up has a cost. Reading sensors, checking timers, writing to flash, or transmitting "just in case" all add up over thousands of cycles.

• The battery wasn't the answer. It would have been easy to install a much larger battery, but I wanted the device to stay small enough to fit almost anywhere. That meant squeezing every bit of efficiency out of the hardware and firmware instead.

After dozens of firmware revisions and more current measurements than I'd like to admit, I finally reached a point where slow reporting intervals could achieve close to a year of operation on a tiny rechargeable battery.

I'm curious—what's the biggest battery optimization you've discovered in your own embedded projects? I'm always interested in learning new techniques.

https://preview.redd.it/ery0a2o4zcah1.jpg?width=4032&format=pjpg&auto=webp&s=b0484c51a2311de6522e8c62638ca3ec3912c053

I recently tested a simple 1/4-wave (868 MHz) antenna made from 0.8 mm silver wire.

In open terrain with clear line of sight ( about 2 meters from ground level ), I was able to maintain a stable link at just over 20 km.

I'm curious about everyone else's results.

I'd love to compare setups and see what's realistically possible.