7 ms·
μWWVB: A Tiny WWVB Station
- anishathalye 10y agoHi HN! I wanted to share the story of µWWVB, a watch stand that I built that automatically sets the time on my atomic wristwatch. Because I can't receive the regular atomic watch radio signal where I live, I built a device that determines the current time by using GPS and then emulates the WWVB protocol to set my atomic watch. In the process of building this, I learned a lot about time, clocks, radio, and WWVB, and so I thought I'd share what I had learned.
- madengr 10y agoVery nice work! Can you receive WWVB via a larger, resonant loop antenna; say a 10 cm diameter solenoid and resonating capacitor? If so, you may be able to place the watch at the center of the resonator (i.e. within the solenoid) so it parasitically couples. The antenna gain will be proportional to area, so much more gain than that of a watch antenna.
- anishathalye 10y agoOh, that's a neat idea! Yeah, I think I should be able to receive WWVB in my dorm room via a larger antenna. I should try it when I'm back in my dorm room after the winter break.
- madengr 10y agoMaybe build one with a short piece of large diameter PVC pipe as the coil form. Use a signal generator at 60 kHz to drive a smaller, transmit probe coil. Then another receive probe coil hooked to an oscilloscope. Use this loose magnetic coupling technique to tune the large coil for resonance. You'll of course want to shoot for as high of Q as possible, but that's an engineering trade off of AC wire resistance, capacitor Q, etc. Go for as large of inductance as feasible, until your self resonance is just above 60 kHz, then pull it to down on frequency with a silver mica cap, or adjustable air variable cap.
- leblancfg 10y agoGreat stuff! I should add, "10s of nanoseconds" took a while to digest. Can I suggest "tens" instead?
- anishathalye 10y agoGood point, I hadn't noticed that. Fixed!
- trav4225 10y agoHi. Thanks for the article! Perhaps I missed it, but I'm wondering why you had to deal with daylight savings at all. Isn't all the time data involved here either UTC or GPS?
- anishathalye 10y agoWWVB includes information about daylight savings time in the information it broadcasts.
- trav4225 10y agoAh, I see. Thank you!
- nathan_f77 10y agoFantastic post! I learned a whole lot by reading this. You also have access to some very nice milling and 3d printing equipment. That is one beautifully designed and soldered PCB.
- amagumori 10y agoelectronic equipment too. i was salivating at that agilent mixed-signal oscilloscope, that's like a $3500 piece of kit. meanwhile i'm over here with my puny rigol ds1052e
- anishathalye 10y agoYeah, I'm lucky to have access to some really nice equipment at the Cypress Engineering Design Studio makerspace at MIT!
- newman314 10y agoThis is cool! Have you given any thought towards building a home GPS powered NTP server? That would be a cool variant on your project.
- grandsham 10y agoThe way that the author uses GPS to get time (NMEA messages) works well for the purposes of the article, eg syncing a wristwatch to ~1 second accuracy. As another poster pointed out though, these messages are only accurate to about a half-step one, and it is actually worse than just using an internet NTP signal. If you want to build a GPS based NTP server, you need a GPS board that outputs a PPS signal. When I built mine I used an adafruit board hooked up to a raspberry Pi's GPIO pins. It's something of a bear to get everything to play together properly and get the extremely precise PPS signal to the NTP server, I recall it required a custom kernel module and a lot of tinkering with tick rates.
- gonzo 10y agoI watched (and guided, some), my son do this in his summer between high school and college. http://store.netgate.com/Lures/GPS.aspx http://store.netgate.com/Lures/GPS.aspx
- mysterydip 10y agoWhile currently I have no use for this, I definitely appreciate the research and effort that went in to solve a localized problem, and sharing the results. Epitomizes hacker culture to me. Thanks for sharing :)
- codewritinfool 10y agoNice work!
- eximius 10y agoGreat work! And I applaud the concise and thorough explanation of the legality regarding the unlicensed transmissions!
- ChuckMcM 10y agoVery nice, I was originally thinking "Gee with NMEA signals they won't be able to do better than 1/2 second accuracy." and then realized its a wristwatch, you don't generally care about milliseconds and the watch can lose or gain a half second in a day anyway! So in fact it is engineered quite well for the requirement. I also liked the antenna solution. Very nice piece of work.
- dragontamer 10y agoThe WWVB protocol has been interesting me for the past few months. I have been thinking about doing the opposite: building my own WWVB receiving station. There are modules which can automatically receive the WWVB radio signal and output the high/low pulses (which still need to be translated from PWM to ones and zeros). https://www.amazon.com/60kHz-atomic-clock-radio-module/dp/B01KH3VEGS https://www.amazon.com/60kHz-atomic-clock-radio-module/dp/B0... ---------- If I were to make a recommendation: you're hiding a bit of magic here: > I designed the board using the EAGLE PCB design software and milled the board from a single-sided FR-1 circuit board blank on an Othermill v2: You haven't said the kinds of endmills you're using (flat square mills? Or did you use a V-tip?). If so, where did you source the V-Tips from? The software side probably had a few extra steps as well (IIRC, its usually Eagle -> Eagle CAM Plugin export -> CAM software -> GCode -> Mill) So expanding on what you did here would be most helpful... to me at least :-) > It’s challenging to design good antennas for such long wavelengths FYI: the loopstick / Small Loop antenna operates on the magnetic-portion of the wave instead of the electric-portion of the wave. Instead of making a very large wire (which "receives" the voltage as the wave passes), the small loop antenna is basically an inductor that generates a current as the magnetic wave passes over it. That's how it gets so small, since the electric wave is 5000-meters long, its a bit difficult to make.
- anishathalye 10y agoAh yes, I didn't go into details on the milling process. I used a 1/64" flat end mill for the traces and a 1/32" flat end mill to cut out the board from the stock. Also, the software workflow was really easy - Otherplan (Othermill's CAM software) can directly import Eagle's .brd files and drive the Othermill.
- dragontamer 10y ago> Also, the software workflow was really easy - Otherplan (Othermill's CAM software) can directly import Eagle's .brd files and drive the Othermill. Hmm, good to know. The only CNC Mill I have access to however is the Nomad 883. So I guess for my purposes, I'd have to do something else. But that's a nifty feature of "Othermill" for sure. > I used a 1/64" flat end mill for the traces I'm glad to know this is feasible for some of these larger surface-mount parts (like an ATTiny44A).
- hackuser 10y agoCould someone provide quick background on WWVB, or at least say if the Wikipedia page is accurate? I clicked the link to the NIST page,[0] which helped a little but was written for someone already familiar with it - it's both too detailed and leaves fundamental questions unanswered; for example: * Is WWVB the norm for consumer clocks that synchronize to an outside source? If I see a clock with that feature, should I assume it uses WWVB? Is it one of several options? * Why not use GPS? Because of poor signal indoors? * How far does this signal from Colorado propagate? [0] https://www.nist.gov/pml/time-and-frequency-division/radio-stations/wwvb https://www.nist.gov/pml/time-and-frequency-division/radio-s...
- zitterbewegung 10y agoTo answer your points 1. WWWVB is the norm. When they say 'Atomic Clock' they are using WWVB to synchronise time. 2. Putting GPS on a consumer electronic would be WAY more expensive. 3. WWVB covers Continental US and Southern Canada. https://en.wikipedia.org/wiki/WWVB#Propagation https://en.wikipedia.org/wiki/WWVB#Propagation
- tjohns 10y ago1. In the US, yes. In other parts of the world, you'll see clocks that instead use a closer station (like DCF77 in Germany). 2. Indoor operation is part of it. Also, GPS receivers are more expensive and power hungry. 3. Depends on time of day, but it generally covers most of North America. There's coverage maps here: http://tf.nist.gov/stations/wwvbcoverage.htm http://tf.nist.gov/stations/wwvbcoverage.htm
- anishathalye 10y agoEDIT: apparently a couple other people have already answered your questions, but I didn't see the other answers because I was typing my response. I'll leave my answer here cause it contains some information not in the other responses. The Wikipedia page seems to be pretty accurate. To answer your questions: > Is WWVB the norm for consumer clocks that synchronize to an outside source? If I see a clock with that feature, should I assume it uses WWVB? Is it one of several options? In the United States, yes. Clocks labeled "atomic clock" or "radio clock" are set up to sync with WWVB. Nowadays, many clocks are multi-band, which means that they are designed so that they can receive from multiple radio stations (there are a bunch of these; see https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time_signal_stations https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time...). Usually, the clock decides which station to try to sync to based on which time zone they are in (which is part of the configuration). For example, my wristwatch, a Casio AWGM100B, can receive from DCF77 (Germany, 77.5 kHz), MSF (UK, 60 kHz), WWVB (United States, 60 kHz), JJY (Japan, 40 kHz / 60 kHz), and BPC (China, 68.5 kHz). > Why not use GPS? Because of poor signal indoors? I think the main reason is that GPS is a lot more complicated, so it requires more sophisticated hardware and software (and more power) to get time via GPS. There are some higher-end watches that do use GPS - for example, the Casio GPW1000-1A. > How far does this signal from Colorado propagate? Depends on weather conditions and time of day. NIST has coverage maps that show where you can get > 100µV/m for different times of the day: http://tf.nist.gov/stations/wwvbcoverage.htm http://tf.nist.gov/stations/wwvbcoverage.htm
- Animats 10y agoThat's the computer hacker solution. The RF hacker solution would be to build something that receives WWVB and retransmits its own signal on the same frequency without interfering with itself. The wavelength is long enough that you could pull this off. This has the advantage that you're not degrading the accuracy of the time signal.
- jrockway 10y agoIt's not that accurate anyway; WWVB doesn't compensate for its propagation delay like GPS time does.
- wl 10y agoWWVB's worst case propagation delay is ~20 ms. This project's error can be up to 500 ms. For a wrist watch or wall clock, the former is imperceptible and the latter is not.
- jrockway 10y agoYeah, the conclusion I reached after making a GPS-based NTP server is that having my clock accurate to a few nanoseconds didn't really matter for anything. My watch is a minute behind my computer right now. Doesn't matter.
- VLM 10y agoThat's a cool project. Something I'd find irresistible is messing with the protocol to find the limits of your watch receiver. I mean sure the spec is 500 ms pulse for a one and 200 ms for a zero, and we can safely assume anything from 499 to 501 ms is close enough, but I wonder how far those limits can be pushed. Is the crossover from understanding 1/0 the arithmetic mean or geometric mean or some arbitrary limits or does the firmware crash or go into easter egg mode or ... Another fun game to play is the AT44A is much weaker than the 8-bit home computers from the 80s that could synthesize live audio in real time up to a couple KHz. A somewhat more advanced chip in the 2010s could numerically synthesize live 60 KHz signals, which might be fun instead of altering hardware PWM. Then you could play with amplitude and keying signals. Its well trodden ground that square wave modulation of a morse code signal is extremely wide bandwidth. A fancy raised cosine would be very smooth. Perhaps you'd get better SNR at the receiver with less keyclicks, so you could reduce power, or it would be more reliable per watt transmitted. Or it might not matter. But live realtime synthesis would none the less be entertaining alternative to modifying PWM registers on the fly. A cleaner yet simple modulation method might be let the PWM fly free and use a digital pot with a I2C interface to smoothly AM modulate the output, probably only cost one chip and might provide some performance gain. Most digital pots are just FET with some buffers and drivers, they seem to be spec'd to 44 KHz sometimes 192 KHz so I assume 60 KHz would be no big deal. Another funny thing about ferrites and reciprocity is how interesting their output is when they saturate, and how low the power level is when they saturate. That's why very little ham radio work has been done with ferrites as transmitting antennas, compared to the more conventional yet still rather obscure air core magnetic loop antennas. Ferrites are cool, strange chemical magic. Anyway a simple air core coil made resonant-ish might work better as an antenna than you'd think, maybe better than the ferrite. You get best performance with the correct ferrite core material for the frequency band selected. Probably the gutted radio clock you used, used the correct core material, or maybe it used the cheapest one that mostly worked (although not in your dorm room as you mentioned). Trying to use Amidon core material 17 would be quite futile at 60 khz, a bar of amidon material #3 would probably work at 60 KHz assuming you could find it. Manufacturing your own optimized antenna large enough core to handle some power and with the proper ferrite core material would be an interesting 3rd experiment. Daydreaming about ways to continue iterating on a design is fun.
- runeb 10y agoCould you attack WWVB receivers by overriding the transmitted signal and change their time? edit: Not something I'd want to do obviously, just seems like a rather insecure technology.
- cvoss 10y agoI believe you can if your signal is strong enough relative to the real one, which can be pretty weak in certain areas (hence the need for this device). My high school's math and science club tried to do this once to the school's clocks as a prank. We never got the transmission circuitry working, but I did write a program for my graphing calculator that computed and outputed the correct signal sequence for a given timestamp through its 2.5mm jack. Edit to add: As I recall, our particular clocks synced at midnight or if you hit the reset button. I think that was to increase the chances of a good signal.
- gravypod 10y agoWhat calculator was that? That sounds like a lot of fun!
- cvoss 10y agoMine was a TI-84, although an 83 would have worked too. I wrote it in native assembly, since TI-BASIC doesn'the give you enough control. You can do clever things with that jack, like play music if you've got a 2.5-to-3.5mm adapter. And yeah, it was a blast!
- camtarn 10y agoPart of the linked page describing the WWVB transmission station which I enjoyed: "A computer is used to automatically tune the antennas during icy and/or windy conditions. This automatic tuning provides a dynamic match between the transmitter and the antenna system. The computer looks for a phase difference between voltage and current at the transmitter. If one is detected, an error signal is sent to a 3-phase motor in the helix house that rotates the rotor inside the variometer. This retunes the antenna and restores the match between the antenna and transmitter." Cool technology :)
- homero 10y agoI'd love to buy one. My house stopped receiving them for a year now. Maybe I have a noise source or something.
- coin 10y ago-1 for disabling zoom on mobile devices