AirTime is a compact, locally deployed time-signal transmitter that synchronizes radio-controlled watches and clocks — even in regions with no national long-wave time service.
Three components, one seamless system
The Raspberry Pi syncs precise time from the internet using NTP via Chrony, ensuring atomic-level accuracy.
The AirTime software encodes the current time into your chosen radio standard (DCF77, WWVB, MSF, or JJY) using the TXTempus library.
The AirTime hat transmits the signal via a ferrite coil (up to 6m) or air coil (up to 10cm), syncing any radio-controlled watch or clock nearby.
Everything you need to keep your watches in sync
Set daily or weekly broadcast schedules. Most watches auto-sync overnight — set it once, forget about it.
Supports DCF77, WWVB, MSF, JJY40, and JJY60. Works with watches from any region, anywhere in the world.
Full control from any browser. Monitor system health, start broadcasts, manage schedules — desktop and mobile optimized.
Adjust the transmitted time by hours and minutes. Compensate for timezone quirks or deliberately set watches ahead.
Hardware schematics, PCB files, and all software on GitHub under AGPL-3.0. Build it, modify it, make it yours.
Toggle all hardware LEDs on or off from the dashboard. Perfect for concealed setups or if blinking lights bother you.
Check for and apply software updates directly from the web interface. One click to stay current with the latest features.
Real-time CPU, RAM, temperature, NTP sync status, ping, and uptime — all visible at a glance on the dashboard.
Transmit any major time-signal frequency, regardless of your location
Covers most of Western Europe, up to Romania. The most common standard for European radio-controlled watches.
Covers North America. Broadcasts in UTC — watches adjust based on timezone setting.
Covers the United Kingdom. Used by British radio-controlled watches and clocks.
Dual-frequency standard covering Japan and surroundings. Used by Casio, Seiko, Citizen, and other Japanese brands.
AirTime is intentionally short-range. It is not a broadcast transmitter — it’s designed for personal, laboratory, workshop, or small-office environments. Users are responsible for ensuring compliance with local emission regulations.
A Raspberry Pi hat with everything you need
A custom PCB that sits on top of a Raspberry Pi Zero 2W. It includes a signal amplifier, status LEDs, a manual sync button, and connectors for your antenna of choice.
Pin assignments, jumper settings, and full assembly instructions are covered in the AirTime documentation (PDF).
Clock, Broadcast Control, System Statistics, and Broadcast Schedule — all at a glance.
Responsive layout adapts to any screen. Manage your AirTime from your phone.
System metrics refresh every 2 seconds. Always know what your Pi is doing.
Works with any radio-controlled timepiece
AirTime works with any radio-controlled watch or atomic clock that syncs via long-wave time signals. Each brand calls it something different — Casio says “Multiband 6”, Citizen says “Radio Controlled”, Seiko says “Radio Wave Control”, and German watches call it “Funkuhr”. If your watch won’t sync because you’re too far from a transmitter, AirTime is your fix.
AirTime also works with radio-controlled wall and desk clocks — sometimes called “atomic clocks” — including models from La Crosse Technology, Bulova, and others. Note that some American-market clocks only support WWVB.
Two paths to your own AirTime
AirTime would not exist without TXTempus, the open-source time-signal transmitter library created by Henner Zeller. TXTempus handles the low-level encoding and transmission of time signals across all supported frequencies and standards (DCF77, WWVB, MSF, JJY40, JJY60). We built AirTime on top of this excellent foundation — adding the hardware hat, web dashboard, scheduling system, and overall user experience.
The amplifier circuit on the AirTime hat is based on a design by Andreas Spiess, who explains the concept in depth in this YouTube video. Huge thanks to both Henner and Andreas for making this project possible.
View TXTempus on GitHubQuestions, orders, or just want to say hi?
Whether you want to order a pre-built unit, have questions about the project, need help with your build, or just want to chat about radio-controlled watches — we'd love to hear from you.