A
digital clock is a type of
clockA clock is an instrument used to indicate, measure, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell"...
that displays the time
digitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
ly, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Usually, digital clocks are associated with electronic drives. (Analog clocks are driven mechanically or electronically.)
Digital clocks typically use the 50 or 60
hertzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
oscillation of
AC powerPower is defined as the rate of flow of energy past a given point. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC...
or a
crystal oscillatorA crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
as in a
quartz clockA quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...
to keep time. Most
digitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
clocks display the hour of the day in
24 hour formatThe 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. This system is the most commonly used time notation in the world today. The 12-hour clock is, however, still dominant in a handful of countries,...
; in the United States and a few other countries a more commonly used hour sequence is
12 hour formatThe 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem The 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem The 12-hour clock is a time...
(with some indication of AM or PM).
A
digital clock is a type of
clockA clock is an instrument used to indicate, measure, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell"...
that displays the time
digitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
ly, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Usually, digital clocks are associated with electronic drives. (Analog clocks are driven mechanically or electronically.)
Construction
Digital clocks typically use the 50 or 60
hertzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
oscillation of
AC powerPower is defined as the rate of flow of energy past a given point. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC...
or a
crystal oscillatorA crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
as in a
quartz clockA quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...
to keep time. Most
digitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
clocks display the hour of the day in
24 hour formatThe 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. This system is the most commonly used time notation in the world today. The 12-hour clock is, however, still dominant in a handful of countries,...
; in the United States and a few other countries a more commonly used hour sequence is
12 hour formatThe 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem The 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem The 12-hour clock is a time...
(with some indication of AM or PM). Digital emulations of analog-style faces exist as well.
Displays
To represent the time, most digital clocks use a
seven-segmentA seven-segment display , less commonly known as a seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays...
LEDLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
,
VFDA vacuum fluorescent display is a display device used commonly on consumer-electronics equipment such as video cassette recorders, car radios, and microwave ovens. Unlike liquid crystal displays, a VFD emits a very bright light with clear contrast and can easily support display elements of...
, or LCD display for each of four
digitsIn mathematics and computer science, a digit is a symbol used in numerals , to represent numbers, in positional numeral systems...
. They generally also include other elements to indicate whether the time is AM or PM, whether or not an alarm is set, and so on.
Setting
One notorious drawback to digital clocks is the difficulty of setting the time in some designs. Therefore in electronic devices where the clock is not a critical function, often they are not set at all, displaying the default after powered on, 00:00 or 12:00.
Moreover, since they run on
electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
, most digital clocks must be reset every time they are moved or the power is cut off. This is a particular problem with
alarm clockAn alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their sleep in order to start their days in the mornings, but can also be used for short naps; they are sometimes used for other reminders as well...
s, since a
power outageA power outage is a short- or long-term loss of the electric power to an area.There are many causes of power failures in an electricity network...
during the night usually results in the clock failing to trigger the alarm in the morning.
To reduce the problem, they often incorporate a
batteryAn electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial...
backup to maintain the time during power outages. More recently, some devices incorporate a method for automatically setting the time, such as using a broadcast
radioRadio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
time signalA time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:One sort of public time signal is, of course, a striking clock...
from an
atomic clockAn atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, and to control the frequency of television...
, getting the time from an existing
satellite televisionSatellite television is television delivered by the means of communications satellite and received by a satellite dish and set-top box. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.-History:The...
or
computerA computer is a machine that manipulates data according to a set of instructions.Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century . These were the size of a large room, consuming as...
connection, or by being set at the factory and then maintaining the time from then on with a quartz movement powered by an internal rechargeable battery.
Uses
- Because digital clocks are very small and inexpensive devices that make product designs more popular, they are often incorporated into all kinds of devices such as radios, television
Television is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission...
s, microwave ovenA microwave oven, or a microwave, is a kitchen appliance that cooks or heats food by dielectric heating. This is accomplished by using microwave radiation to heat water and other polarized molecules within the food...
s, standard ovenAn oven is an enclosed compartment for heating, baking or drying. It is most commonly used in cooking and pottery. Ovens used in pottery are also known as kilns...
s, computers and cell phones. Sometimes their usefulness is disputed: a common complaint is that when time has to be set to Daylight Saving Time, usually many household clocks have to be readjusted.
- In the 1980s and 1990s, digital clocks were standard on most cars.
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