Build Your Own Radio Clock Transmitter

NIST

Deep in the Colorado foothills, there are two radio transmitters that control the time on millions of clocks all across North America. It’s WWVB, the NIST time signal radio station that sends the time from several atomic clocks over the airwaves to radio controlled clocks across the continent. You might think replicating a 70 kW, multi-million dollar radio transmitter to set your own clock might be out of reach, but with a single ATtiny45, just about everything is possible.

Even though WWVB has enough power to set clocks in LA, New York, and the far reaches of Canada, even a pitifully underpowered transmitter – such as a microcontroller with a long wire attached to a pin PWMing at 60kHz – will be more than enough to overpower the official signal and set a custom time on a WWVB-controlled clock. This signal must be modulated, of course, and the most common radio controlled clocks use an extremely simple amplitude modulation that can be easily replicated by changing the duty cycle of the carrier. After that, it’s a simple matter of encoding the time signal.

The end result of this build is an extremely small one-chip device that can change the time of any remote-controlled clock. We can guess this would be useful if your radio controlled clock isn’t receiving a signal for some reason, but the fact that April 1st is just a few days away gives us a much, much better idea.

Comments

  1. Mike says:

    How many people are going to be late for work this April Fools Day because of this?

  2. XOIIO says:

    I just wish I knew someone that had a radio controlled clock.

  3. dlemmink says:

    Wow, great project. Wondering about the legality of a transmitter of this type even at low power. A receiver based on an ATTINY85 would make a very useful device though.

  4. Kuy says:

    I would like to propose an entire HaD category in the theme of “with a single ATtiny45, just about everything is possible.” The Tiny25/45/85 is an amazing chip and is worthy of its reputation as an eight-pin Swiss army knife. This also sounds like it could be a great new contest in the format of the 555 contest!

  5. mikes electric stuff says:

    You may need to hang around a while though – many radio controlled clocks only look for a signal once a day or so to resync their internal timebase.

    • r4k says:

      This. Most “atomic” clocks only enable and poll the radio once a day. The is usually done late at night when longwave reception is at its best. This is why you need to set an approximate time on many clocks before they will sync with WWVB.

  6. Anthony says:

    Most Time Clocks work with that Sync …

    Could be interesting

  7. orenbeck says:

    As a tool to show how Radio Clock works- wonderful work . For the love of Darwin… be mindful of how far these signals can really go. Nope- the inch of wire in a safe demo is not that liable to go major distances at these frequencies. My concern is some cretin who uses a bit more power or better antennas- or just gets Darwin Lucky in re-radiation coupling to other wires!

    I can sketch out a credible risk of a Ham Shack/SW listener or someone with old twinlead fed roof antennas etc having that parasitic coupling. And yes- that gets their clock whacker signal out into danger space. It’s why we used to confine some work to a REAL shield room.

    Yes, it is Damned illegal to screw with such signals and even if you think you got away with no damages- it’s a when, not if about the epic doom. Clock and Location systems can indeed pose a life safety issue in ways approaching impossible to predict.

    There’s a layer beyond mere legal compliance. It’s called thinking of consequences. There’s a quite serious potential for Very Bad Things. As these signals can and DO propagate over astonishing distances, with a scary real potential of you pranging stuff on the other side of town or farther.

    It’s not “just” Lulz to screw up our delicate ballet of interconnections It’s risking a lot more.

    if someone at minimum is late for a schedule as the worst, they’re quite liable to NOT wish you well… If someone DIES from several scenarios that we are supposed to be mindful of preventing, it’s going to not only be jail for the perp-it’s going to rain hell on *ALL Hacking of RF stuff! *

    A proof-of-concept in a sandbox, go for it. A small area of Maker Faire equally cool. Do this in the wider world and you lose all honor=you’re a vandal/belong in jail for reckless endangerment.

    Laugh at my reality check , but be careful, eh?

    • Trui says:

      It would be an extremely far fetched scenario to see someone die as a result of this hack. First of all, 60 kHz signals don’t travel very far unless you have a huge antenna and a lot of transmit power. But most importantly, people at the risk of dying because of reading a bad time should not depend on a single clock that could stop when the battery runs out, or the mains power is interrupted.

    • hodginsa says:

      I agree with you that messing with systems where legality is a concern is probably not a good idea. But can you give a good example where someone is going to die(or even get hurt for that matter) because their clock suddenly changed time? I’m pretty sure the only clock I trust is my cell phone and even then I’m not going to die if its not correct and also it’s not even affected by this.

      Seriously, not being a smart ass, I’m curious at to a specific scenario that could cause a dangerous situation.

      I would like to think that such devices wouldn’t rely on a system like this to keep people out of harms way.

      • sneakypoo says:

        It’s ye olde butterfly effect. A police officer has two clocks, the radio controlled one being his backup. His usual clock fails, the radio controlled one is off by a few hours. He wakes up late and during his drive to work he isn’t in place to prevent an assault on a street corner which he would’ve caught if he had woken up in time.

        It’s not about how low the risk is, it’s about not being a c_nt and making it a risk in the first place.

        • hodginsa says:

          Haha, I hope this is a troll comment. Seriously.

          I understand not being a -insert highly offensive word-, but you just proved my point from the fact you had to refer to the “butterfly effect”. An effect that is based around making everyone at blame for anything that has ever happened in the entire known world.

          There are far worse *legal* pranks you could do to someone than to change the time on their clock. Again I’m not denying that you shouldn’t be messing with people(unless its your friends or they have it coming to them), I merely started this discussion because of the way over the top statement made that this could possibly harm someone. Without creating some absolutely ridiculous slew of events, it would never be the case. People don’t rely on time like that, just look at how everyone is late now-a-days. Time means nothing.

          I was hoping that someone could provide a real situation when this would affect something; like maybe some old school timing device that still relies on these signals to, I don’t know, deliver medicine to someone at a specific time – now that would be dangerous. But the truth is, there isn’t anything like that. Prove me wrong though.

        • vonskippy says:

          ” prevent an assault on a street corner”

          Bwahahahahahaha – a cop actually doing something useful – what country do you live in?

        • Alas says:

          What if its the other way around and the policeman saves a life, because he woke up late?
          This realy reminds me of this Video :)

      • Liam Jackson says:

        The best I can think of is you’re messing with this in a room of which your neighbour has their clock on the joining wall.
        They could be using that clock to tell when to do something like take pills or test blood sugar.
        Some of these radio clocks are sold as ‘science clocks’ or ‘never tells the wrong time’ so people could be misled by the marketing to thinking they can rely on it.

        • hodginsa says:

          That is a very valid response. There are most definitely some people who would buy something like that, maybe an elderly person who is taking meds, and rely on it. Though I’m obviously hoping that is rarely the case.
          Its funny you mention blood sugar because I am diabetic, and there are so many clocks around me I would know pretty quickly if one was reading incorrect. But I’m not too worried about time accuracy in my case. Again though my cell phone is almost always number one, then computer.

      • 1337 says:

        Example… Say you are Sammy Jenkins, and your wife needs her insulin shot at 3pm. And because you keep changing the time to 2:59pm, and sammy can’t remember the last 2 minutes, and his wife thinks he is pretending then bam, you are responsible for her overdose. sinner.

  8. Matthias_H says:

    Overpowering a distant transmitter sounds impressive, but what is the reach?

  9. Simon says:

    Heh, the next generation of these clock signals are going to have to implement a digital signature with the public key in the reciever chip.

  10. anon says:

    Put those GPS receivers into good use by broadcasting accurate time to all local clocks.

  11. orenbeck says:

    Can we be mindful of what responsibility our skills need to have!

    I have personally seen a cell phone in a Chicago Basement Garage link to a Benton Harbor Cell System. Miles per watt arguably up there with this chip’s signal deranging some mere clock a few miles away or closer . Arguing with which band is a fail- it’s watts per mile under consideration.

    How could someone die? How many dangerous things do you know of with a clock in them? And thus a system gets built with potential for a SPOOFED clock to cause disaster. The handful of ones I know about with any chance for risks are bad enough to contemplate.

    Envision the number of systems that we may not KNOW of that are now using such time signals.

    Scared yet? There’s been a move to use over-the air signals in odd places and not all of those uses are sane to let become public knowledge. Sometimes it’s responsibility to not misuse our knowledge. Not censorship- It’s being aware that we can crash systems and kill people too easily to risk it avoidably. Don’t forget- it’s easier to not think first. It’s harder to be a responsible user of our powers but it’s our duty.

    And suspecting we’re kept in the dark can anger us on freedom grounds.

    Sometimes it’s not even deliberate obfuscation so much as no one suspecting signal tampering would ever be a reality. See- clock fail is planned for, not clock spoofing…So maybe the coder never planned for someone bollixing the timedata. Which causes a risk for unimagined havoc that might never happen till some yutz mungs the time stream data. I hope to literal HELL that this stays in theoretical territory and we avoid damages or deaths. That’s my point. SO FAR, we’ve had few reportable incidents of Hackerdom folks doing more than exasperating stupids.

    Many Decades, ago at least one nameless city had reversible traffic lanes controlled in the 11 meter band. More than one whack job tried to exploit the systems. And apocryphal claims of their results ranged from deaths- to mere wasting of the perp’s time. I suspect that a lot was kept deliberately obscure and or disinformation zoned.

    But- yeah- there is a damnably plausible risk to me and as said- don’t risk lives for lulz.

  12. echodelta says:

    I am surprised that those LF signals work at all in a world full of SWPS’s, specially the cheap ones form China. Longwave and the lower 2/3 of the AM band are just awash in buzzzzzz. Now they won’t replace streetlights on sked, they wait till someone complains to an obscure part of their website. Each light buzzes heavy trying to restart, wiping out AM radio for a 9 block area!

    • tekkieneet says:

      They are not supposed to interfere with radio. That’s why FCC part 15 certification is required for anything that operates above 9kHz.

      Not all Chinese made stuff passes or have FCC/UL/CE etc certification. US Custom people should be checking for shipments from China for those types of certifications instead of superficial things that round corners or yellow edges.

  13. Great hack. I tried to hack the Frankfurt’s DCF77 and it worked too. I used 10 MHz crystal oscillator but it might be OK with the internal too. Only it might be a good idea to calibrate the OSCCAL register because the precision of the internal 8 MHz oscillator is poor (mine got 8.33 MHz at 5 V).

  14. asm-wolf says:

    All the exams that I have taken in school and college are moderated with radio controlled clocks. I always wondered if it would be possible to creep the clock back a few 10s of minuets over the several hours that the exam takes place with a spoofed signal for extra time. I may have to experiment with my own clocks out of curiosity.

  15. Davros says:

    EVERY clock I have ever encountered is *NOT* “radio controlled” !
    They run off (as someone else pointed out), an INTERNAL quartz
    oscillator – and invariably powered by a AA battery !

    Aside from tech geeks, who would pay extra for a “WWV” capable
    receiver in a clock ? answer – NO ONE!

    On the other extreme, most “mission critical” applications (read,
    public safety or business IT networks), get their timing (again as
    pointed out by others) from GPS satellites that are picked up by
    very expensive 19″ rack mount receivers (think TRAK9100) that
    provide an NTP stratum-2 signal to the network.

    Basically this ‘hack’, is a waste of time, and more fodder for the
    clueless legislators and media to sensationalize and paint another
    “evil hacker” scenario.

    • buttim says:

      Radio controlled clock are quite common, give a second look (I own one). Don’t explain about quartz oscillators to hackaday’s reader, that’s pointelss: they know better. Radio control is about periodical resyncing, not time keeping, you missed the point.

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