2. 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parts have been replaced by a vibrating quartz crystals controlled by minute electronic circuits.
Quartz is naturraly 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 vibrate up to 32,768 cycles per cecond 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.
Each one-second pulse triggers the microship 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 crystal display (LCD). This is a thim 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 digits is formed from segement ¡--up to seven are
normally used.
The liquid crystals rearrange their molecules according to whether or not they are charged by electricity.
When the conductors carry no charge, ligth 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 realing and twist the light away from the reflective Surface, appering
black. Together, the charged segements therefore appear as figures.
3. The electronics of a digital watch many be contained in a simple integrated circuit. However,
we can think of the chip as a number of separate units, each performing a different function.
This can be shown in a block diagram.
The Oscillator generates pulses at a fixed frequency of 32,768Hz. This frequency is determined
by the natural oscillation of the quartz cristal. The divider circuits perform binary division on
the pulses to reduce their frequiency to one pulse per second. A binary count of these pulses
is made by the counter circuits and the decoders convert the binary output into signals which
ligh up the appropriate segments of the digital display.Di
Dividers
Dividers form one of the main components of this system. They consist of circuits which
switch between two stable states and are known as bistables or flip-flops.
4. Each time a pulse is applied to the clock input of a flip-flop, its outputs change their logic state from high
(logic 1) to low 8logic 0) or viceversa. This means that two clock input pulses cause one pulse to be ouyput
from the flip-flop at output Q, as shewn in fig. 3
The frequency of the clock inout pulse is therefore divided by two at the Q output, i.e. The flip-flop is
acting as a binary frequency divider.
If the Q output of the flip-flop is fed into the clock input of another flip-flop, the pulse frequency is again
divided by two.
The output of one flip-flop is connected to the input of the next, i.e. They are connected in cascade . The
output frequency at Q2 is one quarter of the input pulse frequency at CK.
The frequency of the oscillator pulse in a digital watch can be reduced from 32,768Hz to 1Hz by using
fifteen cascaded flip-flops
5. Approximation
exercises
Read the text again to match each unit to its function.
1. Oscillator a. Divides the frequency 15 times.
2. Divider b. Produces signals to operate the LCD.
3. Counter c. Displays the time.
4. Decoder d. Produces fixed frequency pulses.
5. LCD e. Makes a binary count of the pulses.
7. Digital time display
Digital watch
Instead of using the
complicated springs, cogs,
and wheels of a mechanical
watch, the digital watch uses
a vibrating criytal to keep
time. It is accurate to one
Second in 10 years.
Liquid cristal display
Hours
Diagrams
Seconds
Calendar
Buttons enable watch
to display time and
date, buzz several daily
alarms, count down
from 24 hours, and act
as a stopwatch with an
accuracy of 1/100th
ssecond.
8. Label each step in the flowchart below, which ecplains how a digital watch works. The
first step has been labelled for you.
Quartz chip
The voltaje applied to a
quartz chip makes it
expand and contract,
producing vibration.
Power source
The power to make the quartz
chip vibrate comes from
battery which lasts at least one
year.
Quartz chip
Quartz crystal
e
Vibrating criystal
Inside vacuum capsule, the
quartz chip vibrates at a
steady frequency of 32768
vibrations a second.
Microchip
The frequency is halved 15
times, resulting in one
pulse per second.
Contacts for side
switches
Liquid cristal display (LCD)
Each pulse advances the
display in one-second
intervals.
a) The pulse is fed to an
LCD.
b) The display advances
in one-second
intervals.
c) The quartz criystal
expands and
contracts.
d) The frequency is
halved fifteen times
by a microchip.
e) A voltaje is applied to
a quartz criytal.
f) This results in a
frequency of one
pulse per second.
g) The cristal vibrates at
a frequency of 32,768
per second.
c
g
d
f
a
b
9. Liquid crystal displays
Liquid cristal displays work by
blocking light by polarization, the
same effect as ratating one lens of the
other. A small electric charge across
the two bits of glass changes the
polarization of the liquid crystak in
between and blackens the display.
Study this diagram which explains the operation of liquid crystal display. The link each set of statements using words or
phrases de your own to make your own explanation. Omit unnecessary words and make any other changes required.
Glass
Polaroid
Metallic coating
Liquid crystal
polaroid
Metallic coating
Glass
Aluminium
Contacts to chip
• A liquid cristal display (LCD) Works like sunglasses.
An LCD blocks light by polarization.
• An LCD is a thin film of liquid.
It reacts to electricalcharges.
• It is placed in a glass sándwich.
The sándwich has a top layer of plain glass and a bottom layer of reflective glass.
• Trasparent electrical conductor separate the crystals into segments. The segments form each digit.
• Any digit can be formed.
Up to seven segments are used.
• The crystals are charged.
Their molecules are arranged in one way.
• The crystals are not no charged.
Their molecules are arranged in another way.
• The conductors carry no charge.
light is reflected out again
The display is blank.
• The conductors are charged.
The molecules in the charged segments twist.
They block light from the reflective Surface.
Thet appear black.
• The charged surfaces appear as figures.
10. Preguntas, texto y profundización.
1. Here Voltage is applied to quartz crystal.
2. The quartz crystal expands and contracts.
3. The crystal vibrates at a frecuency of 32, 768 per second.
4. The frequency od halved fifteen times by a microchip.
5. This result in a frequency of one pulse per second.
6. The pulse is fed to an LCD.
7. The display advances in one-second intervals.
The relationship was previously with Task 3
11. Digital watch-Application
The digital clock is an application that relates seen above, but with the difference
that (Digital watch ) will be virtual and will be used in mobile.
Esto fue traído gracias a la pagina Androidpit mas información aquí.
http://www.androidpit.es/aplicacion/com.Phantom.TheMr
