For those living in the continental US who, for whatever reason, don’t have access to an NTP server or a GPS device, the next best way to make sure the correct time is known is with the WWVB radio signal. Transmitting out of Colorado, the 60-bit 1 Hz signal reaches all 48 states in the low-frequency band and is a great way to get a clock within a few hundred nanoseconds of the official time. But in high noise situations, particularly on the coasts or in populated areas these radio-based clocks might miss some of the updates. To keep that from happening [Mike] built a repeater for this radio signal.
The repeater works by offloading most of the radio components to an Arduino. The microcontroller listens to the WWVB signal and re-transmits it at a lower power to the immediate area, in this case no further than a few inches away or enough to synchronize a few wristwatches. But it has a much better antenna for listening to WWVB so this eliminates the (admittedly uncommon) problem of [Mike]’s watches not synchronizing at least once per day. WWVB broadcasts a PWM signal which is easy for an Arduino to duplicate, but this one needed help from a DRV8833 amplifier to generate a meaningfully strong radio signal.
Although there have been other similar projects oriented around the WWVB signal, [Mike]’s goal for this was to improve the range of these projects so it could sync more than a single timekeeping device at a time as well as using parts which are more readily available and which have a higher ease of use. We’d say he’s done a pretty good job here, and his build instructions cover almost everything even the most beginner breadboarders would need to know to duplicate it on their own.
Cool project, though txtempus can already do this and only needs an RPi zero. I use it to sync all my watches and a clock a meter away from the nightstand.
Yep, that’s the one I use also. Aside from the RPi, needs just 3 resistors and some wire.
It syncs using NTP, so useful where there is no WWVB signal (but there is wifi).
https://github.com/hzeller/txtempus
“a clock within a few hundred nanoseconds of the official time”
Only if you’re withing a few hundred feet from the transmitter!
I live 6 milliseconds away from Fort Collins. My “atomic” clocks are always slow.
You need faster atoms.
Suburban Boston here. Comes in great sometimes, not so great most of the time. NTP is my go to, WWVB is nice to have.
I’m also in Boston. The older clocks I have that use the regular amplitude modulation are very spotty, but the one clock I have that can receive the recently (ish) added phase shift modulation work perfectly every day. Wish more devices / watches could decode PSK.
I’m surprised there isn’t a slightly more modern version of this, that can be received with more standard equipment, and could also carry emergency alerts and time zone info.
Maybe they could have high power Bluetooth advertising directly from satellites.
Well, gps is a thing. But not alerts.
lol, using a h-bridge as the driver is pretty interesting. makes sense really, FETs designed for logic level inputs. Nice hack, though.
Just a heads up that chip generates its own clock for its current limiting PWM feature, something to be aware of if you continue to experiment with this chip for RF. “Where’s that mixing product coming from?” type questions — probably that.
This is really cool project. I’d quibble with the description though. It doesn’t use “a much better antenna for listening to WWVB” and retransmit that signal, instead it uses ntp or gps to get time and cleverly encodes a low power wwvb compatible signal for nearby devices. Even better than repeating imo since this could be used anywhere in the world to sync devices expecting to recieve wwvb.
I have an older “atomic” radio clock that sets it’s to the WWVB time out of Colorado any time it’s plugged in. Over the years the time set has drifted. First one minute fast, then two. A couple years ago it quit drifting further and now ALWAYS reads exactly 5 minutes past the actual WWVB signal time. Unplug it to drain power, plug it back in, give it a minute to find signal and sync time then BOOM exactly 5 minutes fast again.
It’s really interesting to me how this oddity occurs. Has anyone seen this before or have a possible explanation? I’ve considered some strange interplay between the 60 kHz carrier wave, the pulse-width modulation and amplitude-shift keying of the signal along with the data rate but I still don’t have any clue what factors could cause a 5 minute variation in demodulating and decoding the WWVB time signal.