Open-source electronic conspicuity for general aviation: ADS-L 4 SRD-860 for aircraft (skyBlip) and ground stations (skyPost).
docs/BEHAVIOR.md lists every claim the firmware makes about itself, straight from the host test suite that checks them. It is generated, so it cannot describe a behavior that stopped being true.
docs/TUNING.md is the other half: every number that behavior is tuned by, with the line of source that justifies it. Also generated, from the constants themselves.
skyBlip Go runs on the LilyGO T-Echo Plus, the reference board for the tracker. The other devices and the board they share are on skyblip.eu/devices.
| T-Echo Plus (skyBlip Go) | |
|---|---|
| Processor | Nordic nRF52840, Cortex-M4F, 64 MHz |
| GNSS | Quectel L76K, PPS |
| 868 MHz radio | Semtech SX1262 |
| Barometer | Bosch BME280 |
| Inertial unit | Bosch BHI260AP |
| Display | 1.54" e-paper, 200x200 |
| Audible alarms | buzzer + vibration motor |
| Bluetooth | BLE 5.0, 3 connections, no pairing |
| USB | USB-C |
| Battery | 2400 mAh Li-ion |
| Directory | What lives there |
|---|---|
firmware/ |
the C++ tree: core/, ui/, ports/, the Zephyr platform, the host test suite, and the simulator's world |
simulator/ |
the development harness page that drives the WASM build of the firmware, and device.css, the case both it and the site draw the panel in |
website/ |
skyblip.eu, a Rails app that Parklife renders to static files |
docs/, schemas/, scripts/, skyship/ |
the generated behavior and tuning indexes, the wire schemas, the build and release tooling, the artwork |
The firmware and the site share a tree so that a change in behavior and the page documenting it can land in one commit. They do not share a build: each has its own workflow, gated on the paths it owns.
The host test suite and the simulator need nothing but a C++ compiler: make -C firmware test, make -C firmware simulator.
The device image is built off a committed ref, main by default, into builds/:
scripts/build_local.sh # skyblip_go, the only product today
SKYBLIP_REF=HEAD scripts/build_local.sh
The first run needs cmake ninja dtc gperf, then bootstraps a Zephyr workspace under ~/.cache/skyblip/west and installs the SDK under ~/.local/opt.
CI builds it too, and which key signs it decides which units it can update over Bluetooth (firmware/keys/):
- a pull request: a key made for the run, so the build is proven and the image updates nothing;
main, or a branch run by hand: the development key, published byfirmware.ymlas a pre-release on the Releases page,dev-<build number>formain(the last three kept) anddev-<build number>-<branch>for a branch (its newest kept until its pull request closes);- a
v*tag onmain: the production key, after an approval, into a draft release (release.yml). The tag must equal the product'sVERSION.
The build number after the + is the commit count. A unit on the production key refuses an image older than the one it runs, so it only goes up or installs the same version again. A unit on the development key takes any development image, older ones included. Drag-and-drop of a .uf2 takes either anywhere.
Three identifiers name skyBlip to the outside world, and one of them is ours so far.
- ADS-L address table: entry 58, applied for at
registry@ads-l.aeroand described on skyblip.eu/ads-l-registry. Pending: until the registry answers, 58 is a value we chose, held in one constant infirmware/core/settings/address.h. - USB: Vendor ID 0x1209, Product ID 0x5AFE, granted by pid.codes (pidcodes/pidcodes.github.com#1282) and set in
firmware/products/skyblip_go/prj.conf. It names the running application only: the bootloader presents Adafruit's factory descriptors. - NMEA manufacturer code: open. The
$PADSL,$PADSIand$PADSOsentences sketched on skyblip.eu/ads-l-registry/nmea need a three-letter code that NMEA assigns: either one of our own, or an ADS code held by ADS-L's registry or working group, so the sentences belong to the specification rather than to one implementer.
skyBlip stands on a decade of open work by the free-flight community. Thanks to the authors of the projects we learned from while building it:
- Paweł Jałocha: the ADS-L reference implementation and nrf52-ogn-tracker
- Linar Yusupov: SoftRF
- Moshe Braner: the SoftRF fork
The repository is MIT: see LICENSE. The one exception is firmware/, which is GPL-3.0-only under firmware/LICENSE, and that license reaches everything below it: core/, ui/, ports/, hardware/, runtime/, products/, boards/, test/ and the simulated world in firmware/simulator/.
So the schemas, the build and release scripts, the simulator page and the website may be copied into a closed product; a tracker built from this firmware owes its sources.
The simulator page is MIT, but what simulator/ builds is not: make -C simulator build copies the firmware's WASM into simulator/build/, and that binary stays GPL-3.0-only wherever it is served.
"skyBlip" and "skyPost", the wordmark and the airship mark in skyship/ are trademarks of François Catuhe. The licenses above grant copyright permissions, not trademark ones: a fork may say it is compatible with skyBlip or derived from it, and may not use the names or the marks to name its own product or to suggest endorsement.
Copyright (C) 2026 François Catuhe