Keeping Time With A Spring Powered Integrated Circuit

Seiko Spring Drive Movement Being Assembled

Watch aficionados have a certain lust for mechanical watches. These old school designs rely on a spring that’s wound up to store energy. The movement, an intricate set of gears and other mechanical bits, ensures that the hands on the watch face rotates at the right speed. They can be considered major feats of mechanical engineering, with hundreds of pieces in an enclosure that fits on the wrist. They’re quite cheap, and you have to pay a lot for accuracy.

Quartz watches are what you usually see nowadays. They use a quartz crystal oscillator, usually running at 32.768 kHz. These watches are powered by batteries, and beat out their mechanical counterparts for accuracy. They’re also extremely cheap.

Back in 1977, a watchmaker at Seiko set off to make a mechanical watch regulated by a quartz crystal. This watch would be the best of both words. It did not become a reality until 1997, when Seiko launched the Spring Drive Movement.

A Blog To Watch goes through the design and history of the Spring Drive movement. Essentially, it uses a super low power integrated circuit, which consumes only 25 nanowatts. This IC receives power from the wound up spring, and controls an electromagnetic brake which allows the movement to be timed precisely. The writeup gives a full explanation of how the watch works, then goes through the 30 year progression from idea to product.

Once you’ve wrapped your head around that particularly awesome piece of engineering, you might want to jump into the details that make those quartz crystal resonators so useful.

[Thanks to John K. for the tip!]

16 thoughts on “Keeping Time With A Spring Powered Integrated Circuit

  1. Wait – mechanical watches are not, in my experience “quite cheap”. That description does not fit at all. Also doesn’t make sense in context – did the author mean “quite expensive”?

      1. I too have been a bit obsessed by what it would take to do this as a DIY clock. 25 nanowatts is pretty impressive, but if a project could work at even multiple orders of magnitude more power one could use gravity potentially. Some of the common watches have a 72 hour power reserve which works out to only 0.00648 joules. The equivalent work done by gravity moving 1 kg over 0.661 millimeters. Imagine we scale it up the energy requirements 1000 times, then were still talking 1kg moving 661 mm = 66 cm < 1 meter, for 72 hours of runtime.

        I'm wondering if anyone else out there has been playing with this idea…

  2. In case you were wondering why it’s 21st century and we still don’t have flying cars, efficient sustainable energy sources and the space program is a joke: they were busy for 40 years making a watch. Good job.

  3. It is not correct to suggest quartz is always more accurate than mechanical, in fact there are so many quartz timepieces who’s accuracy is awful, even ones in not too cheap devices.

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