Making · 2026
A flight tracker that fits in a pocket
Firmware for a card-sized ESP32 computer that shows live air traffic as a radar scope, a sortable list, and a detail card per aircraft — with a watchlist, logging to an SD card, and proximity alerts.
What this is
The M5Stack Cardputer is an ESP32-S3 with a small screen and a keyboard, about the size of a credit card. This firmware turns it into a live aircraft tracker: it pulls position reports from the OpenSky Network over WiFi and draws them.
It is a network client, not a receiver. The ESP32 can’t demodulate the 1090 MHz signal aircraft broadcast — that’s what the RTL-SDR receiver on my desk is for. This is the version you can carry.
Five screens
- Radar — a polar scope centred on you, with range rings and heading vectors. The sweep line doubles as a countdown to the next data poll.
- Traffic — a dense list: callsign, altitude, speed, distance, climbing or descending.
- Flight — everything about one aircraft. Emergency transponder codes raise a red banner.
- Watchlist — saved callsigns, each marked airborne or out of range.
- Settings — edited on the device and kept in non-volatile storage.
The constraint that shaped it
The data source is rate-limited: anonymous access allows roughly one poll every three and a half minutes, and a free account about one every 25 seconds. On a device with a few megabytes to work with, the design is mostly about spending a small budget well — poll interval, search radius, and how much of each response to keep in memory.
OpenSky also dropped password authentication in early 2026 in favour of OAuth2 client credentials, so the firmware implements the token flow on the microcontroller.