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Analog And Digital System
A string tied to a doorknob would be an analog system. They have a value that changes steadily over time and can have any one of an infinite set of values in a range. If you put a measuring stick or ruler at a specific point along the string, you can measure the string's value every so many seconds at that point. When you watch it move, you will see it moves constantly. It doesn't instantly jump up and down the ruler.
A digital system would be to flick the light switch on and off. There's no 'in between' values, unlike our string. If the switch you are using is not a dimmer switch, then the light is either on, or off. In this case, the transmitter is the light bulb, the media is the air, and the receiver is your eye. This would be a digital system.
Analog And Digital Signal
An analog signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. An analog signal is a datum that changes over time-say, the temperature at a given location; the depth of a certain point in a pond; or the amplitude of the voltage at some node in a circuit.
In analog technology, a wave is recorded or used in its original form. So, for example, in an analog tape recorder, a signal is taken straight from the microphone and laid onto tape. The wave from the microphone is an analog wave, and therefore the wave on the tape is analog as well. That wave on the tape can be read, amplified and sent to a speaker to produce the sound.
In analog signal the value could change between a negative value to positive or from zero to a positive value.
It can refer to discrete-time signals that are digitized, or to the waveform signals in a digital system. Digital signals are digital representations of discrete-time signals, which are often derived from analog signals. A discrete-time signal is a sampled version of an analog signal, the value of the datum is noted at fixed intervals (for example, every microsecond) rather than continuously.
In digital technology, the analog wave is sampled at some interval, and then turned into numbers that are stored in the digital device. On a CD, the sampling rate is 44,000 samples per second. So on a CD, there are 44,000 numbers stored per second of music. To hear the music, the numbers are turned into a voltage wave that approximates the original wave.
The digital signal only recognises values at or around 2 points and interprets them as a logic 1 or 0.