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Raspberry Pi Pico balloon tracker

Balloon tracking
My main hobby is flying weather balloons, using GPS/radio trackers to relay their position to the ground, so they can be tracked and hopefully recovered. Trackers minimally consist of a GPS receiver feeding the current position to a small computer, which in turn controls a radio transmitter to send that position to the ground. That position is then fed to a live map to aid chasing and recovering the flight.

This essential role of the tracker computer is thus a simple one, and those making their own trackers can choose from a variety of microcontrollers chips and boards, for example Arduino boards, PIC microcontrollers or the BBC Microbit. Anything with a modest amount of code memory, data memory, processor power and I/O (serial, SPI etc depending on choice of GPS and radio) will do. A popular choice is Raspberry Pi, which, whilst a sledgehammer to crack a nut for tracking, does make it easy to add a camera.

When I see a new type of processor board, I feel duty bound to make it into a balloon tracker, so when I was asked to help test the new Raspberry Pi Pico, doing so was my first thought. It has plenty of I/O – SPI ports, I2C and serial all available – plus a unique ability (not that I need it for now) to add extra peripherals using the programmable PIO modules, so there was no doubt that it would be very usable. Also, having much more memory than typical microcontrollers, it offers the ability to add functions that would normally need a full Raspberry Pi board – for example on-board landing prediction. More on that later.

Tracker components
So a basic tracker has a GPS receiver and radio transmitter. To connect these to the Raspberry Pi Pico, I used a prototyping board where I mounted a UBlox GPS receiver, LoRa radio transmitter, and sockets for the Pico itself.

I don’t use breadboards as they are prone to intermittent connections that then waste programming time chasing a “bug” that’s actually a hardware problem. Besides, trackers need to be robust so I would need to solder one together eventually anyway.”

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