Mike Burton's "Watch Tower" Turns an Espressif ESP32 Into a WWVB-Compatible Radio Time Transmitter

Google engineering manager Mike Burton has built a very literal "Watch Tower" — a 3D-printed Espressif ESP32-powered gadget designed to take control of radio-synchronized wristwatches.

"There are some beautiful radio-controlled watches available these days from Citizen, Seiko, Junghans, and even Casio," Burton explains. "These timepieces don't need fiddling every other month, which is great if you have more than one or two and can never remember what comes after 'thirty days hath September…'"

In the US, radio-synchronized watches tend to work through the WWVB longwave time signal, broadcast by the National Institute of Standards and Technology (NIST) out of Fort Collins, Colorado on a 60kHz carrier wave. This, however, doesn't cover the whole of the US reliably — and with poor reception in the San Francisco Bay Area, largely due to a radio-noisy environment, Burton was looking for a way to improve reliability.

"I wanted to build something that could cover my whole watch stand and be based on a more familiar toolset for the typical hobbyist, namely USB-based 32-bit microcontroller development boards, Wi-Fi, and Arduino," Burton explains. "My goal was to make something approachable, reliable, and attractive enough it could sit with my watch collection."

The result is the Watch Tower, a compact device that can serve as a watch holder while also beaming out its own WWVB-compatible signal to nearby timepieces. "The FCC requires a license to transmit," Burton notes of the legality of overriding the actual WWVB signal, "but has an exemption for 60kHz transmitters as long as the field strength is under 40μV/m at 300 meters. You will definitely not exceed this limit."

Inside the 3D-printed housing is an Adafruit QT Py ESP32, though Burton says most Espressif ESP32-based boards compatible with the Arduino IDE should work. The tower part hides a ferrite rod antenna tuned to 60kHz, plus an H-bridge serving as an amplifier — strong enough when fed with a USB power supply to deliver usable signals to watches within an 8-10 inch radius. "If you need more power. Burton notes, "you can use an external power supply. I found the signal to be strong enough without it and preferred the convenience of a single USB power supply."

The project is documented in full on GitHub, including 3D print files for the enclosure and the full source code, under an unspecified license; a simulation is available on Wokwi for the curious.