Instead of using the complicated springs, cogs, and wheels of a mechanical watch, the digital watch uses a vibrating crystal to keep time. It is accurate to one second in 10 years.

liquid crystal display hours

digital time display

seconds

calendar

Task 2 Make a survey of your class to find out how many are wearing digital watches

and which functions these watches can display.

Some questions to ask:

Does it show the day and date? Does it have a 12/24-hour option?

an alarm?

a reminder? Can you use it as a stopwatch? Does it count down from 24 hours, etc.?

Task 3 Label each step in the flowchart below, which explains how a digital watch

works. The first step has been labelled for you.

quartz crystal

quartz chi

Power source

The power to make the quartz chip vibrate comes from a battery which lasts at least one year.

Vibrating crystal

Microchip

The frequency is halved 15 times, resulting in one pulse per second.

contacts for side switches

Liquid crystal display (LCD)

Each pulse advances the display in one-second intervals.

Inside vacuum capsule, the quartz chip vibrates at a steady frequency of 32 768 vibrations a second.

a The pulse is fed to an LCD.

b The display advances in one-second intervals.

с The quartz crystal expands and contracts.

d The frequency is halved fifteen times by a microchip.

e A voltage is applied to a quartz crystal.

f This results in a frequency of one pulse per second.

g The crystal vibrates at a frequency of 32,768 per second.

Task 4

Read this text to check your answers. Then compare answers with your neighbour.

Digital watch

The traditional mechanical wristwatch uses a balance wheel and hairspring to keep time. In a digital watch these mechanical parts have been replaced by a vibrating quartz crystal controlled by minute electronic circuits.

5 Quartz is a naturally occurring mineral and one of its major sources is Brazil. However, to avoid impurities, the crystals used in watches and clocks are usually created (or 'grown') under controlled conditions. One of the advantages of quartz is that it is very stable.

The artificial quartz crystals used in digital watches are designed to 10 vibrate up to 32,768 cycles per second when the current from a battery is passed through them.

These vibrations produce electric pulses. As the pulses travel through the electronic circuits of the microchip, their rate is gradually halved. The result creates a pulse rate of one per second.

15 Each one-second pulse triggers the microchip to send signals to the digital display to advance the numerals by one second.

The pulses are also used to control different functions such as the hour display, date and alarm signal.

Most modern quartz watches display the time in digits on a liquid 20 crystal display (LCD). This is a thin film of liquid which reacts to electrical charges placed between two sheets of glass. The bottom layer is reflective glass.

Transparent electrical conductors separate the crystals into segments. Each digit is formed from segments— up to seven are normally used.

25 The liquid crystals rearrange their molecules according to whether or not they are charged by electricity.

When the conductors carry no charge, light is reflected out again, so the display will be blank. When the conductors are charged by an electric pulse, the molecules in the charged segments realign and 30 twist the light away from the reflective surface, appearing black. Together, the charged segments therefore appear as figures.

Language Study Cause and effect, 3

Here are the statements from Task 3 in the correct sequence. What is the relationship between them?

1. A voltage is applied to a quartz crystal.

2. The quartz crystal expands and contracts.

3. The crystal vibrates at a frequency of 32,768 per second.

4. The frequency is halved fifteen times by a microchip.

5. This results in a frequency of one pulse per second.

6. The pulse is fed to an LCD.

7. The display advances in one-second intervals.

These statements form a cause and effect chain. Note how we can form the links in this chain.

Link 1. In Unit 19, we studied cause and effect links with make:

1+2 A voltage is applied to a quartz crystal making it expand and

contract.

Link 2. In Unit 12, we studied transitive verbs like produce. Often these verbs can be used to form a cause and effect link:

1+2 + 3 A voltage is applied to a quartz crystal making it expand and

contract, producing vibration at a frequency of 32,768 per second.

Link 3. In Unit 16, we studied how to use result in to link a cause and effect when both are noun phrases. Note how this verb is used here:

4+ 5 The frequency is halved fifteen times by a microchip resulting in a

frequency of one pulse per second.

Link 4. When can also link a cause and effect, as in the example which follows. But be careful: one action happening after another does not always indicate that the first action causes the second.

6+ 7 When the pulse is fed to an LCD, it advances the display in one-

second intervals.

We can describe the complete chain as:

A voltage is applied to a quartz crystal making it expand and contract, producing vibration at a frequency of 32,768 per second. The frequency is halved fifteen times by a microchip resulting in a frequency of one pulse per second. When the pulse is fed to an LCD, it advances the display in one-second intervals.

Task 5 Study this circuit, which provides a means of monitoring pressure in a system.

Changes in pressure trigger a warning.

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