13-12-2010, 04:06 PM
Abstract
A digital clock is a type of clock that displays the time digitally, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Digital clocks are often associated with electronic drives, but the "digital" description refers only to the display, not to the drive mechanism. (Both analog and digital clocks can be driven either mechanically or electronically, but "clockwork" mechanisms with digital displays are rare.) The biggest digital clock is the Lichtzeitpegel ("Light Time Level") on the television tower Rheinturm Düsseldorf, Germany.
An 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 night'ssleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but most clocks automatically stop the alarm sound if left unattended long enough. A classic analog alarm clock has an extra hand or inset dial that is used to specify the time at which to activate the alarm.
Traditional mechanical alarm clocks have one or two bells that ring by means of a mainspring that drives a gear that propels a hammer back and forth between the two bells or between the interior sides of a single bell. In some models, the back encasement of the clock itself acts as the bell. In an electric bell-style alarm clock, the bell is rung by an electromagnetic circuit and armature that turns the circuit on and off repeatedly.
Digital alarm clocks can make other noises. Simple battery-powered alarm clocks make a loud buzzing or beeping sound to wake a sleeper, while novelty alarm clocks can speak, laugh, sing, or play sounds from nature.
Some alarm clocks have radios that can be set to start playing at specified times, and are known as clock radios. A progressive alarm clock, still new in the market, can have different alarms for different times (see Next-Generation Alarms). Most modern televisions and cell phones have alarm clock functions to turn on or make sounds at specified times.
References:
http://en.wikipediawiki/Digital_clock
http://en.wikipediawiki/Alarm_clock