Watching the sky over Barcelona — one transponder at a time
On a balcony in Barcelona there's a small antenna, a Raspberry Pi, and a receiver that spends its days listening to the sky. I built it to pick up every aircraft transponder within range — hundreds a day — and feed them to a bot that decides, in real time, which ones are actually worth talking about.
Most traffic is routine: another A320 on approach, another regional hop. This project skips right past it. What it looks for is different — military movements, emergency squawks, rare or historic airframes, the occasional flight with a story behind it. When it finds one, it builds a composite image from the live radar track and a real photo of that exact aircraft, writes a caption, and posts it across Instagram, Bluesky, and Mastodon.
It's a small, self-contained pipeline — receiver, classifier, image compositor, multi-platform publisher — designed, built, and run end to end from that one balcony.
In the last 30 days, 4127 aircraft came within range of our little antenna. We picked out 39 of them (0.9%) as worth telling you about.