How quartz watches and clocks work (2024)

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You are here:Home page >Gadgets >Quartz watches and clocks

by Chris Woodford. Last updated: July 14, 2023.

You may not believe in astrology, butthere's no question the planets rule our lives. We get up when the Sun rises (or some timeafter) and go to bed when it sets. We have a calendar based ondays, months, and years—periods of time that relate to how theMoon and Earth move around the Sun in the sky. For most of history,people found this kind of "astronomical timekeeping" good enough fortheir needs. But as the world became ever more frantic andsophisticated, people needed to keep track of hours, minutes, andseconds as well as days, months, and years. That meant we neededaccurate ways of keeping time. Pendulum clocks and mechanicalwatches used to be the best way of doing this. Today, many people usequartz clocks and watches instead—but what are they and how do theywork?

Photo: Quartz is really cheap and the clocks that use it need hardly any moving parts. That's why it's now used in even the most inexpensive timepieces. Because it's so accurate and reliable, it's very much a selling point—which is why clocks like this proudly have the word "quartz" plastered prominently across their dials. Note that this is an analogclock (one with hands): quartz clocks and watches don't have to be digital (have numeric displays).

How ordinary clocks work

We all know that a clock keeps time, but have you ever stopped tothink about how it does so? Probably the simplest clock you couldmake is a speaking clock. If you count seconds by repeating a phrasethat takes exactly one second to say (Like "elephant one", "elephanttwo", "elephant three"...), you'll find you can keep time prettyaccurately. Try it out. Say your elephants from one to sixty and seehow well you keep time over a minute, compared to your watch.

Not bad, eh? The trouble is, most of us have better things to do allday than say "elephant." That's why people invented clocks. Some of theearliest clocks used swinging pendulums to keep time. A pendulum is along rod or a weight on a string that swings back and forth. In 1583,the Italian physicist Galileo Galilei (1564–1642) discovered that apendulum of a certain length always takes the same time to swing backand forth, no matter how heavy it is or how big a swing it makes. Hefigured this out by watching a huge lamp swinging on a chain from theceiling of Pisa Cathedralin Italy, and using his pulse to time it as it movedback and forth. In a clock, the pendulum's job is to regulate the speedof the gears (interlocking wheels with teeth cut into their edges).The gears count the number of seconds that pass and convertthem into minutes and hours, displayed on the hands that sweep roundthe clockface. To put it another way: the gears in a pendulum clock arereally just counting elephants.

Photo: Pendulum power: This swinging rod (with a weight at the bottom) is what keeps the time in a grandfather clock. It was one of the great discoveries we owe to Galileo.

You can make a pendulum clock by tying a weight to a piece ofstring. If the string is about 25cm (10 inches) long, the pendulum willswing back and forth roughly once each second. Shorter strings willswing faster and longer strings slower. The trouble with a clock likethis is that the pendulum will keep stopping. Air resistance andfriction will soon use up its energy and bring it to a halt. That's whypendulum clocks have springs in them. Once a day or so, you wind up aspring inside the clock to store up potential energy to keep the pendulum movingfor the next 24 hours. As the spring uncoils, it powers the gearsinside the clock. Through a see-saw mechanism called an escapement,the pendulum forces the gears to turn at a precise rate—and this is howthe gears keep time. A pocket watch is obviously too small to have apendulum inside it, so it uses a different mechanism. Instead of apendulum, it has a balance wheel that turns first one way andthen the other, controlled by a much smaller escapement than the one ina pendulum clock.

You can find out more about all this in our separate article on pendulum clocks.

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How quartz clocks work

Photo: Crystals of quartz.Photo by courtesy of US Geological Survey.

The trouble with pendulum clocks and ordinary watches is that youhave to keep remembering to wind them. If you forget, they stop—and youhave no idea what time it is. Another difficulty with pendulum clocks is that theydepend on the force of gravity, which varies very slightly from place to place;that means a pendulum clock tells time differently at high altitudes from at sea level!Pendulums also change length as the temperature changes,expanding slightly on warm days and contracting on cold days, which makes them less accurateagain.

Quartz watches solve all these problems. Theyare battery powered and, because they useso little electricity, the battery can often last several years before you need to replace it.They are also much more accurate than pendulum clocks. Quartz watcheswork in a very different way to pendulum clocks and ordinary watches.They still have gears inside them to count the seconds, minutes, andhours and sweep the hands around the clockface. But the gears areregulated by a tiny crystal of quartz instead of a swinging pendulum ora moving balance wheel. Gravity doesn't figure in the workings at all so a quartz clocktells the time just as well when you're climbing Mount Everest as it does when you're at sea.

Photo: The quartz oscillator from a watch. You can see how small it is by looking at the very last photo on this page. This is the part numbered "5" in that picture.You can see what's inside the container—effectively a little electronic tuningfork—in two great Wikimedia Commons photoshereandhere.

Quartz sounds exotic—with a "q" and a "z," it's a great word to play inScrabble—but it's actually one of the most commonminerals on Earth. It's made from a chemical compound called silicondioxide (silicon is also the stuff from which computer chips are made),and you can find it in sand and most types of rock.Perhaps the most interesting thing about quartz is that it's piezoelectric.That means if you squeeze a quartz crystal, it generates a tinyelectric voltage. The opposite is also true: if you apply a voltage toa piece of quartz, it vibrates at a precise frequency (it shakes an exact number of times each second).

Photo: Maybe you have a decorative, violet-colored amethyst crystal like this in your home? It's a type of quartz that gets its color from iron substituting for some of the silicon in pure quartz.

Inside a quartz clock or watch, the battery sends electricity to thequartz crystal through an electronic circuit.The quartz crystal oscillates (vibrates back and forth) at aprecise frequency: exactly 32768 times each second. Thecircuit counts the number of vibrations and uses them to generateregular electric pulses, one per second. These pulses can either power anLCD display (showing the time numerically) or they can drive a small electric motor (a tiny stepping motor, in fact), turning gear wheels that spin the clock's second, minute, and hour hands.

Inside a quartz clock

In theory, it works like this:

1. Battery provides current to microchip circuit
2. Microchip circuit makes quartz crystal (precisely cut and shaped like atuning fork) oscillate (vibrate) 32768 times per second.
3. Microchip circuit detects the crystal's oscillations and turns them intoregular electric pulses, one per second.
4. Electric pulses drive miniature electric stepping motor. This converts electrical energy into mechanical power.
5. Electric stepping motor turns gears.
6. Gears sweep hands around the clockface to keep time.

In practice...

And this is what the inside of a quartz watch looks like in reality.Don't, under any circ*mstances, take yours apart if you ever want it to work again. You cannot see all these parts just by taking the back off a watch.The watch shown here came free with a packet of cornflakes (seriously!) and it was broken before I opened it up.But it was even more broken afterwards...

1. Battery.
2. Electric stepping motor.
3. Microchip.
4. Circuit connects microchip to other components.
5. Quartz crystal oscillator.
6. Crown screw for setting time.
7. Gears turn hour, minute, and second hands at different speeds.
8. Tiny central shaft holds hands in place.

How does the motor work?

If you have a battery-powered quartz clock that's broken and you feel like taking it apart,you may be able to see exactly how it works, because the parts are very much bigger and, with the battery in place, it's often possible to see the stepper motor in action.

Here's the stepper motor from a typical quartz alarm clock. In the left photo, you can see just the static bit of the motor (the bit that doesn't move), whichcomprises the copper-colored coil at the top and the silver-colored arms of what looks like a tuningfork running through it. The metallic coil magnetizes and unmagnetizes the two silver arms, which are thestator (static part) of the motor.

Photo: Left: The stator of the stepper motor. Right: The completed motor with the rotor (white gear) safely in place.

In the right photo, I've put the rotating partback into the motor. It's a little circular-shaped permanent magnet with a north pole and a south pole (which you can't see) and a white plastic gear bonded to the top. As the quartz pulses drive the motor, the stator is magnetized and unmagnetized, and attracts or repels the circular permanent magnet, flicking it around once a second, driving the other gears that, in turn, spin the hands of the clock.

This particular clock broke in a really helpful way, leaving the mechanism largely intact. Put a battery in it and you can hear the once-per-second pulses and see the little white gear rotating in time with them, so it's very obvious how it's working. Put the gears back one by one and you can see how the once-per-second quartz pulses tell you the time!

Photo: With the gears back in place, it becomes clear how the completed clock actually works: the stepper motor drives the small white gear at the top (the rotor), which then powers the bigger gears in turn (and more gears hidden from view), which spin the hands round the clock.

Why is a quartz clock so noisy?

It's no surprise why old-fashioned pendulum clocks make their characteristic "tick-tock" sound: they have mechanical pendulums and escapements rattling back and forth. If you're wondering why some quartz clocks tick so loudly when their key component is a crystal, vibrating at a much higher frequency than people can hear, look no further than the clunky stepper motor. In the clock picture above, the stepper motor is really noisy and its once-per-second vibrations are amplified by a poorly designed plastic case that, I suspect, acts a bit like the resonant case of a guitar.

Why do quartz watches gain or lose time at all?

If quartz is so amazing, you might be wondering why a quartz watch doesn't keep time with absolutely accuracy forever.Why does it still gain or lose seconds here and there? The answer is that the quartzvibrates at a slightly different frequency at different temperatures and pressuresso its timekeeping ability is affected to a tiny degree by the warming, cooling, ever-changing world around us.In theory, if you keep a watch on your wrist all the time (which is at more or less constanttemperature), it will keep time better than if you take it on and off (causing quite a dramatic temperature changeeach time). But even if the quartz crystal could vibrate at a perfectly constant frequency, the way it's mounted in its circuit, tiny imperfections in the gearing, friction, and so on can also introduce minute errors in timekeeping.All these effects are enough to introduce an inaccuracy of up to a second a day in typical quartz clocks and watches(bear in mind that a second lost one day may be compensated by a second gained the next day, so the overall accuracy may beas good as a few seconds a month).

But how does the quartz crystal bit actually work?

You might find that enough of an explanation and, if so, you can stop reading now.What follows is a more detailed discussion of how the quartz crystal oscillatoractually works for those who want to a bit more depth. I should warn you that unless you have a degree in electronicengineering, quartz crystal circuits get very complex very quickly. I'm going to give you avery brief, simplified version of what's happening and some pointers for further reading so youcan dig deeper if you care to.

The key thing to remember about quartz is that it's piezoelectric:it will vibrate when you put electricity into it, or it will give out electricity when you vibrate it.A quartz crystal oscillator uses piezoelectricity in both ways—at the same time!

The way I've drawn my diagram up above makes it look like the quartz crystal is separate fromthe microchip circuit but, in reality, the crystal is an intimate part of that circuit, wired into itby two electrodes. You can see them clearly in the large photo of the watch's insides and in thephoto of the oscillator itself: they're the two little silver-colored legs poking out from the cylindrical metalcase. In effect, the quartz crystal oscillator is just another component wired into the microchip circuit, just like a resistor or a capacitor.

I say "circuit" but it's simplest to think of the oscillator as being part of two separate circuits, both of which are on the same microchip. The first circuit (we'll call it the input) stimulates the quartz crystal with bursts of electricity.Feeding electricity into quartz makes it vibrate (or, if you prefer, oscillate or resonate)through what's sometimes called the reverse piezoelectric effect (where electricity produces vibrations).The oscillator is set up so the quartz vibrates exactly 32768 times a second.But now remember the normal piezoelectric effect: when a piece of quartz vibrates,it generates an electrical voltage. The second circuit on the microchip detects this "output voltage"(fluctuating 32768 times a second) and divides its frequency to produce once-a-secondpulses that drive the motor powering the gears. In a watch with a digital display, instead of using gears, a chip repeatedly divides the oscillator frequency to drive the hours, minutes, and seconds segments (as shown in the artwork below).

Artwork: How a quartz oscillator drives a digital watch with an hours and minutes display and a flashing colon between them ("12:32") to indicate the passing seconds. The oscillator (yellow) vibrates 32,768 times a second. A binary divider (blue, left) divides this by two 15 times (so that's 32768 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 ÷2 = 1)to create a 1 Hz (one per second) pulse that drives the flashing colon. The 1Hz signal from the divider is itself divided by 60 to make minutes and another 12 to make hours. These signals operate a series of drivers (red) that power the segments in the digital display. Artwork from US Patent 3,863,436: Solid state quartz watch by Jack Schwarzschild and Raymond Boxberger, Timex. February 4, 1975, courtesy US Patent and Trademark Office.

In one early form of quartz oscillator, the quartz crystal had two sets of electrodes mounted on it. The first set wasconnected to the input circuit and fed electricity into the crystal to make it vibrate. When the crystalvibrated, it generated a piezoelectric voltage. That was detected by the second set of electrodes (stuckto a different part of the same crystal) and fed to the output circuit.When quartz technology was miniaturized for use in compact wristwatches, it became clear that smalleroscillators were needed and there wasn't room for two pairs of electrodes. That's why modern oscillatorsuse a single pair of electrodes both to stimulate the crystal with energy and detect its vibrations.

That's as much as I'm going to tell you. If you want to find out more, you might like to take a look at the followingsources. Be warned that they are complex and hard to follow unless you have some knowledge of electronic engineering.

Further reading

General

• Crystal oscillator: A detailed introduction from Wikipedia. This is one of those slightly baffling Wikipedia articles likely to make sense only to people who know enough about the subject to write the article in the first place. Nevertheless, it's a reasonable starting point for further research.
• The Crystal Clock by W. A. Marrison, Proceedings of the National Academy of Sciences of the United States of America, Vol. 16, No. 7 (Jul. 15, 1930), pp. 496–507. One of the earliest papers on quartz crystal technology, written by one of its pioneers.

History

• The Evolution of the Quartz Crystal Clock by Warren A. Marrison, The Bell System Technical Journal, Vol. XXVII, pp. 510–588, 1948. This is a superb, fascinating, definitive, and detailed paper setting out the history of quartz timekeeping. But note that it is a complex article from a technical journal. [Archived via the Wayback Machine and available in various other formats from the Internet Archive.]
• Modern developments in precision clocks by A. L. Loomis (Loomis Laboratory) and W. A. Marrison, IEE Electrical Engineering, Vol. 51, No. 2, February 1932. Another classic account from the archives by two of the key pioneers. (Subscription article electronically uploaded in 2013.)
• Variations and Combinations: Invention and Development of Quartz Clock Technologies at AT&T by Shaul Katzir, Icon, International Committee for the History of Technology (ICOHTEC), Vol. 22 (2016), pp. 78–114. A detailed look at how quartz clocks came to be developed by Warren Marrison and his colleagues.

Patents

• Patent #1,472,583: Method of maintaining electric currents of constant frequency by Walter G. Cady, US Patent and Trademark Office, 1923. Cady was an American physicist who helped to pioneer practical uses of piezoelectricity, including crystal oscillators.
• Patent #2,133,642: Electrical system by George W. Pierce, US Patent and Trademark Office, 1924. Pierce was a Harvard physicist who made a number of important contributions to electronics in the early 20th century. This key patent of his includes a definitive (but extremely detailed) description of how various different Pierce oscillators (one of the more popular types of oscillator circuits) work.

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Find out more

On this site

• Clockwork (windup) mechanisms
• Pendulum clocks
• Piezoelectricity

Books

• About Time by Adam Frank. Oneworld, 2013. A whistle-stop history of clocks from sundials to quantum clocks.
• Time Warped by Claudia Hammond. HarperCollins, 2013. How do we perceive time—and is it true to say that our sense of time is "all in the mind"? Essentially, a pop-sci guide to the psychology of time.
• The History of Clocks & Watches by Eric Bruton. Book Sales, 2004. A short introduction to clocks, ancient and modern.
• Pip Pip: A Sideways Look at Time by Jay Griffiths. HarperCollins, 2000. How we experience time as our lives pass by. An offbeat, thought-provoking guide to how time paces through our lives and vice-versa.

Articles

• The Consumer Electronics Hall of Fame: Casio F-91W Wristwatch by Brian Santo. IEEE Spectrum, November 7, 2019. Celebrating an accurate, affordable digital watch.
• A brief history of timekeeping by Edward Green. BBC News, 26 August 2004. A quick history of modern sports timekeeping.
• The Quartz Analog Watch: A Wonder Machine by H. Richard Crane. The Physics Teacher, November 1993. A brief overview, with some good diagrams, and a simplified explanation of how the tiny stepper motor in a watch works.

Patents

For much deeper technical detail, try:

• US Patent 3,863,436: Solid state quartz watch by Jack Schwarzschild and Raymond Boxberger, Timex. February 4, 1975. This relatively easy to understand patent describes a typical modern electronic watch with a digital display. Figure 3 and the accompanying text show how the signal from a 32,768 Hz quartz oscillator is repeatedly divided by an integrated circuit chip for the hours, minutes, and seconds drivers that power the display.
• US Patent 3,803,828: Resistor trim for quartz oscillator by Eugene Keeler and Robert Shapiro, Timex. April 16, 1974. This earlier patent describes a typical "trimming" circuit through which a quartz oscillator can be used to power a watch with high accuracy.

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Text copyright © Chris Woodford 2006, 2023. All rights reserved. Full copyright notice and terms of use.

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