Electronic Driver Replaces Master Clock

In these days of cheap microprocessors and easy access to accurate timing through NTP or from the likes of MSF, WWVB, or DCF77, it’s no problem to ensure that any number of clocks keep the same time. In a simpler age though they didn’t have these tools at their disposal, so when a large organisation wished to ensure that all its parts ran on the same time they used an electromechanical solution. A master clock of as high a quality as the clockmakers of the day could build was fitted with a microswitch. The switch would send pulses to slave clocks which had a solenoid where a traditional clock has a pendulum. Thus every clock in the system lost or gained time at the same rate.

[Edo Lelic] has a rather nice Iskra slave clock, but unfortunately not the master that once drove it. Undeterred by this setback, he’s created an electronic driver board that generates the required 100mS pulses. His weapon of choice was a PIC microcontroller and an H-bridge driver to deliver their required voltage and polarity. The clock was designed to accept 100V pulses, but since it has an internal series resistor he determined that the solenoid was happy with a mere 24V. Source code is available, downloadable at the bottom of the linked article.

These clocks are an unseen piece of technology that is disappearing without our noticing. If you find one – or even better if you find a master clock – you’ll find it to be a very high quality timepiece indeed. A master clock would be well worth snapping up. At least now you won’t have to look too far for a driver for it.

We haven’t seen too many projects like this here at Hackaday. Save for a rather nice digital master clock build, it’s uncharted territory. Almost justification for a Retrotechtacular piece, perhaps.

Thanks [Muris Pučić] for the tip.

13 thoughts on “Electronic Driver Replaces Master Clock

  1. you will need to update your sources.
    WWVB receivers are no longer available to hobbyists in the US.
    After 6-months of searching, I had to order a receiver from the UK.
    Go figure……. (thanks tla[1])

    [1] three letter agency

    1. OK, I’ll bite–why would a new 60kHz clock be perceived as important enough to keep out of the hands of the masses–(because someone mentioned GPS I can make an educated guess)–and isn’t that kind of hard, because they were available for years? It would be kind of like regulating the manufacture of rotary dial telephones: they’re hard to find new, but a motivated individual sould be able to accumulate a basement full of used working units in a relatively short time.. If you get what I mean. I’ll bet a dollar to a donut there’s multiple, late seventies magazine articles on making a WWVB module from that-era’s chips that would get our job done (I think I still have an old Favag slave clock around that needs this treatment) The history of The Self Winding Clock Company and the Western Union Time System is a good online read and would make for a good retrotachular if hackaday has not previously posted a write-up.

      1. The last company making parts for hobby consumption (C-Max, with their CME6005 part) seems to no longer be making them, which pretty much leaves WWVB experimentors to either hack open an already-made radio clock, or build from a 70’s-era design. Both are risky though, as in 2012, WWVB changed the way it broadcasts, which apparently broke a number of older (technically non-compliant but still working) designs.

  2. All that cheap stuff from China will will be hacked to defeat US. Dammed be the misguided efforts of those three letter agencies. I keep my eye open for a flea market clock radio that has that feature. Then I replace the radio with a relay and mains power outlet.

  3. At this point GPS is cheaper and more accurate than WWVB anyway.

    This technology goes back to the mid 19th century. Western Union leased clocks that would automatically wind themselves and would reset the hands to 12:00 with a pulse supplied daily at noon via telegraph lines.

    I’ve been on the lookout for a reasonably priced clock of that sort to drive with an R.Pi and NTP, but those clocks are rare and expensive at this point.

  4. This clock works on 1-minute pulses, not 100ms. This should be corrected in the article :-)
    “In the firmware, we simply count 60 seconds and issue a pulse to the slave clock. This basically advances the minute-hand, and that’s about it.”

  5. How fitting to use an ancient PIC16F84 with an antique clock :)

    I did the same once, with a small clock running on one AA size 1.5V battery. The motor needed alternating pulses, low to high and high to low. That’s easily done using two pins:
    00 at rest
    01 advance one second
    11 at rest
    10 advance one second.

  6. Analog slave clocks are NOT “…an unseen piece of technology that is disappearing without our noticing” – as you declared HaD.

    New models of analog master-slave clock systems are still manufactured and still in demand for new and existing commercial office and government buildings, as well as schools. There are plenty of manufacturers and integrators of master-slave clock systems today. In the U.S., Simplex Time Solutions and American Time are two just off the top of my head.

    If you want to build your own master-slave system you can buy the slave clocks and hack up your own master. If you want, you can even integrate your own analog slave clocks. You start buy buying a slave movement and add the rest yourself. New slave movements can be either copies of time-honored and now informally-standardized systems, or modern movement designs. The vintage compatible slave movements are usually used to build new slave clocks for existing systems, or to repair broken vintage clocks.

    Look up “American Time” on the web for a source of slave clocks and movements. Look up “Hanson Corporation” on the Web and take a look at their Type-C synchron resettable movement as a modern analog slave example.

  7. I have a couple of similar clocks rescued from telephone exchanges, really regretted never managing to steal an exchange master clock as they were glorious pieces of engineering but I think a lot of the old boys would have them away as a retirement present to themselves.

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