How do Quartz watches work?

What is the mystery surrounding the number 32,768?

For a watch enthusiast, a mechanical watch would always be way superior compared to quartz. The reasons are fair enough, a watch that has such tiny intricate parts, each more with a purpose not more, not less important than the other, working together in harmony on top of that it be mechanical is a sight to hold, and a “machine to wear on your wrist.“

Have you ever wondered how a Quartz watch might work? Yeah, they are way cheaper than mechanical ones with fewer components and are considered depreciating assets, but considering the technology, the availability, and the affordability, one cannot deny that the quartz watch is one of the most important inventions not only in the world of watchmaking or timekeeping but for mankind.

Quartz

Before we dive into the mechanics and workings of how a quartz watch works, it’s very important to first understand the root element on which the entire pyramid stands.

What is quartz and how is a material used so frequently in making jewelry, artifacts, and hand stone carvings responsible for accurately telling time, and keeping time better than a mechanical watch?

Quartz, believe it or not, is the second most abundant mineral in the world, just behind feldspar, while there are different variest of quartz, it’s a crystalline mineral made up of silica, quartz is a hard six-sided, prism-shaped structure that is particularly pleasing to look at, and maybe that’s the reason the Romans believed it to be “permanent ice”

Piezoelectricity

Enough of the history, quartz is the first piezoelectric crystal and what is piezoelectricity? Well, it’s basically magic.

Magic? What if I tell you, that if you compress a quartz crystal at just the right angle you’d be able to generate a voltage across! How is that even possible? Well, let’s take a look at what is quartz made of, and its structure.

Quartz is made up of silicon dioxide, and the silicon-oxygen atoms are continuously linked together which forms a symmetry, but one such symmetry this structure forms is a hexagonal shape where silicon and oxygen atoms are placed alternate to each other to form a hexagonal shape.

The silicon atoms are positive while the oxygen atoms are negative, so when we compress a crystal of quartz, all the negative charges are shifted in one direction and all the positive charges in the other direction. Due to this charge separation between the net positive and net negative charges, an electric field will be created leading to a small voltage across it.

Any crystal can be piezoelectric as long as it fulfills some criteria like there should be polar bonds, i.e. some atoms should be slightly positive, while others should be slightly negative. The symmetry matters, for instance, in the above diagram we can notice that opposite to an oxygen atom is a silicon atom and vice-versa. This phenomenon should be attained for a crystal to be piezoelectric. What’s even more intriguing about this effect is that it is reversible, if you apply a voltage to a quartz crystal it will change shape.

Jacques Curie and Pierre Curie discovered this property in 1880.

Learned enough about piezoelectricity? now let’s jump back to why this is so crucial for one to understand the workings of a quartz watch.

How it all comes together

it’s all about vibrations and oscillations, in a pendulum clock, we know that one pendulum swing equals one second, and in a mechanical watch, this pendulum is replaced by the balance wheel, which constantly winds and unwinds and in turn helps to “tick the tock”. Now that we understand that it is important to know the period of vibrations or oscillations to help derive time, let’s look at how quartz helps with this.

In our school, we surely would have experimented with vibrations and how they are formed, and the most common way we created their vibrations was with the help of a tuning fork!

When we hold a tuning fork and flick it, vibrates but we might notice how after a certain period the vibration dies. To keep time we use quartz crystal cut in the shape of a very small tuning fork which is made to vibrate. 

if you make a quartz tuning fork vibrate, its frequency would be too high for humans to listen, but the magic of piezoelectric crystal is when the quartz tuning fork vibrates, it’ll produce a detectable oscillating voltage! different from any other tuning fork whose vibration dies after some time, the piezoelectric tuning fork generates an oscillating voltage which is fed back to the tuning fork, and this is how it keeps vibrating.

Now that we know how it keeps vibrating, the watchmaking industry makes sure that its frequency is 32,768 Hz.

But why 32,768?

Well, there are a few reasons why it beats at exactly 32,768. number one being noticed by all the math nerds out there is that the number is a power of 2, 2¹⁵ to be precise, why 2? And why 2 to the power 15??

2¹⁵ is just above the range of frequency humans can hear, and 2¹⁴ is 16,384 which is audible. 2 because it is easier to divide down to 1hz.

To dial down the 32,768hz down to 1hz a series of flip-flops are used which cut down the frequency by half with each passing flip-flop. Once you’re down to 1hz it is used to move the second's hand and therefore used to keep time!