My son pointed at a cheap little desk clock — one of those tiny ESP-powered gadgets with a square colour screen — and asked if it could show the planes flying over our house, “like a radar.” That’s the best kind of project brief: small, concrete, and genuinely delightful if you pull it off. So I did.

The result is custom firmware running on the clock itself: it pulls live aircraft positions from a free flight-tracking API, and draws a proper radar scope — home in the centre, aircraft as blips on distance rings, a sweep line, callsigns, altitude colours, and an alert when something passes directly overhead.

Fitting it on an ESP8266

The clock runs an ESP8266 — even more constrained than the ESP32s I usually reach for. The big risk was whether it could even make an encrypted API call without running out of memory, since flight data comes over HTTPS. It could, but only with care: a generous receive buffer, streaming the JSON through a filter instead of loading it whole, and fetching just the aircraft within a 30-mile radius of home every few seconds. Memory stayed stable across hours of running.

Three bugs that were really lessons

The black screen. My first firmware drew nothing at all. The display controller needed a specific SPI mode that the obvious library defaults got wrong; the panel was also mounted upside down and needed its colours inverted. None of that is guessable — the fix came from finding a known-good configuration for that exact panel and matching it. Embedded displays are fussy, and “it’s the wiring” is often “it’s one config flag.”

The planes that wouldn’t move. Some blips sat frozen near the centre and confused my son (and me). I pulled the raw data and found the culprit: they were real aircraft, but ones parked on the ground at the airport a few miles away, being drawn as if they were flying. The airport was close enough to be inside our radar range. Filtering out anything marked on-the-ground cleaned it up — and it was a nice reminder to always check your data against reality before blaming your code.

The flickering sweep. The rotating radar sweep flickered horribly, because the little screen has no back buffer — every full redraw flashes. The fix was to stop redrawing the whole screen each frame and instead only erase and repaint the thin sweep line, restoring the rings and blips behind it. Change only the pixels that change. That single idea is behind a huge amount of smooth graphics, and it’s satisfying to implement it by hand on hardware primitive enough to force you to.

Why I love this one

No career angle, no security lesson — just a dad writing firmware so his kid can watch planes on a five-pound clock. But it quietly exercised real skills: constrained networking, embedded graphics, reading an API, and debugging by checking assumptions against ground truth. The best learning projects are the ones someone you love actually wants to exist.

Tech: ESP8266, ST7789 display, Arduino, a free flight-tracking API over HTTPS, over-the-air updates.