Mechanical oscillators vs. electronic clocks

Apr 26, 2008 06:58 GMT  ·  By

Quartz watches, like many other innovative inventions of their time, appeared as high-tech gadgets, some of which were even more expensive than a car. However, as time went by and technology evolved even further, quartz watches became so inexpensive that companies actually gave them away for free as incentives. In the last two decades, quartz watches moved away from LED or LCD high-tech displays towards a more traditional display and mechanism, and are again gaining ground as highly priced items.

As you probably already know, watches rely on oscillators to keep time accurately. Fixed frequency oscillators are also known as time bases or clocks - this is why the frequency of a microprocessor is often called a clock. Some of the first watches that appeared used as oscillators a complex mechanical mechanism formed of two main components, the spring - providing power to keep the clock going - and the oscillating mass - a pendulum, or a wheel oscillator. The oscillating energy was mechanically transferred to the hands on the dial through a gear mechanism with the role of slowing down the clock frequency.

These types of watches are generally known as wind-up watches. Their time keeping accuracy is greatly related to the stability of the clock frequency and the precision of the gear reduction mechanism. Of course, that means there is always the problem of constantly having to wind up the spring mechanism to keep the clock working.

Quartz oscillators

In the middle of the 20th century, the Bulova watch company came up with a brilliant idea: to replace the entirety of the mechanical workings of clocks with electronic circuitry powered by transistor oscillators. Aside of being extremely precise, electronic clocks have the advantage of being powered by batteries, meaning that one doesn't need to be always winding it up in order to work. However, there were still problems. Electronic circuits were still bulky at the time and integrated circuits had just appeared and were relatively expensive, while the LED displays drained battery power very rapidly.

Although quartz crystals provide an accurate time base, there was still the issue of finding the optimum oscillating frequency. Quartz is the common name for silicon dioxide mineral. It is one of the few substances occurring naturally that experiences the piezoelectric effect, meaning that, while under mechanical pressure, is able to generate a voltage on its surface, and vice versa, when a voltage is applied it starts to change shape.

Quartz oscillators are usually shaped into tiny bars or disks in order to reduce air coupling and enhance clock stability. In quartz watches, for example, the quartz crystal oscillator is shaped into a small fork, to reduce the oscillating frequency and therefore the power required to operate it. The clock frequency produced is ran through impulse divisors, electronic counters and then printed on the LCD display.

Alternatively, quartz watches may harness the clock frequency in order to power a small electric motor, that drives the hands on a classic watch dial.

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A classic dial quartz watch
Quartz (SiO2) occurs naturally on Earth
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