Analog vs. Digital Signals fundaments

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Signals can be categorized into two types – analog and digital. But what sets them apart? How can they be used in different applications? Which one of them is better? All of these questions will be answered in this blog post so make sure you give it a good read till the end, if you wish to explore the world of analog and digital signals!

What Are Signals?

Signal is, to put it concisely, an information transmitted via varying (in most cases) voltage between two electronic devices. Depending on the program, which in this case can be defined as a "dictionary" for different values of signal, signal processing occurs and the device can communicate to us a desired output. However, signals are not necessarily linked to electronic devices only. A great example of analog signal transmission can be a thermometer - via its physical characteristics mercury expands or gets contracted hence, if calibrated correctly, being able to display to us the temperature in our ambient. 

What Are Analog Signals?

Analog signals are continuous signals i.e. it is a time-varying signal where the quantity it is representing (e.g. current, voltage, power) varies with time. If you look at the graph of an analog signal, you would see that it is a continuous plot which has a defined value at every time instance. The best example of analog signals is human voice. If you look at the graph of an audio signal, you will see that it is a continuous signal, having a value at every time instance.

Analog signal

Graphical representation of an analog signal credits to CC license from SparkFun

What Are Digital Signals?

Digital signals are discrete signals which usually have only two values – high and low (1 and 0). If you look at the graph of a digital signal, you will see a square wave which is varying between two points and does not take any other value. A binary signal that can only take a value of 1 or 0 is a perfect example of digital signals.

Analog signal

Graphical representation of a digital signal credits to CC license from SparkFun

Properties of Analog and Digital Signals

The properties of analog and digital signals are what sets them apart. A few properties are listed in the table below. These will help you differentiate between the two signals very easily.

Property

Analog Signals

Digital Signals

Continuity

Analog signals are continuous in time

Digital signals are discrete in time

Bandwidth

Bandwidth of analog signals is high

Bandwidth of digital signals is low

Security

Analog signals offer less security, data theft is possible

Digital signals provide high security, encryption is possible

Values

Analog signals can take both positive and negative values

Digital signals usually do not take negative values

Waveform

Analog signals are usually sinusoidal in shape

Digital signals are mostly square pulses

Ease of Reproduction

Analog signals are difficult to reproduce if polluted with noise because of their continuous nature

Digital signals are easily to reproduce if polluted with noise, because they have only two levels

Power Requirements

Equipment using analog signals require more power

Equipment using digital signals require less power

Speed

Data transmission rate of analog signals is slow

Data transmission rate of digital signals is fast

 

Analog vs. Digital Equipment

Since the two types of signals are completely different in nature, they have different equipment because of different signal processing requirements. Equipment that works on two logic levels are said to use the binary system and these are mostly computers and equipment which work with computers such as CD players. Similarly, equipment which rely on continuous signals are analog equipment such as VCR and tape players.

CD players read 1s and 0s which are present in the CDs and convert them into audio signals. On the other hand, tape players use a film of tape present in cassettes, which has analog data magnetically embedded on the tape. The tape player converts the analog data into audio signals.

Analog-to-digital converters (ADC) and digital-to-analog converters (DAC) are used to connect analog devices to digital and vice versa. These converters are widely used in signal processing blocks, such as the ones used in telecommunication systems.    

Analog vs. Digital Quality

When we talk about quality of a signal, the first thing that pops up in our minds is noise. Which signal is more immune to noise? If we look at the signal waveform, we can say that digital signals are more immune to noise. Why is that so?

When noise strikes any signal, it changes the waveform at that point and to remove noise from the signal, an original copy of the signal needs to be produced. Now, consider that noise is produced in a digital signal and it distorts the waveform such that at one point where the signal had to be at a high level, it is somewhere between the mid and the high level. By performing some simple calculations, it can be easily determined that the signal had to be at a high level and hence, the original signal can be reconstructed easily.

On the other hand, if an analog signal is distorted by noise, it will go unnoticed because the signal is already a series of ups and downs hence, it is difficult to differentiate the noisy signal from the original one.

So, we can conclude that the quality of digital signals is better than analog signals because of noise immunity.

Applications of Analog and Digital Signals

Analog signal devices are every day less frequent in the mainstream market due to the signal speed and noise limitations, however in some applications they still are deemed to be superior to digital signals due to their fidelity of the representation. Examples of such are audio recording, where analog recorders by some are considered as higher quality than digital.

Digital signals, on the other hand, are used in computers, smartphones and digital electronics. They usually process data as bits hence, we use the terms megabits, gigabits and so on, for measuring the capabilities of digital electronic devices. Digital signals are widely used these days as compared to analog signals because of their fast data rates and noise immunity.   

Analog vs. Digital Sensors

Sensors measure a physical quantity and respond to it by producing an output such as a voltage. Analog sensors are those which produce an analog signal based on what they sense. Similarly, digital signals are those which produce a digital signal in response to what they measure at the input.

Some common examples of analog sensors are light sensors (LDRs), sound sensors, pressure sensors, and analog temperature sensors. Similarly, there are some commonly used digital sensors such as digital temperature sensors and digital pressure sensors.

To select a sensor, you must first know what type of project you are working on. If the project involves working between two voltages only, then digital sensors are a good choice but if you require continuous signals, then an analog sensor is what you need.

Arduino Applications

You can use both analog and digital sensors in Arduino projects. Digital sensors must be used with the digital I/O pins while analog sensors need to be used with the analog I/O pins.

Sound sensors can be used with Arduino boards to build numerous interesting projects such as clap controlled LED lights. Similarly, light sensors can be used to build a lot of home automation projects.

For digital sensors, we can use the digital temperature sensor to build a home heating system which regulates the indoor temperature between a range of values such as 25 ⁰C to 30⁰C. The sensor works by measuring the temperature and then producing a corresponding voltage that turns the cooling system either on or off, thus working at two discrete levels.

By now, you must have understood how analog and digital signals differ and what are their applications. Analog signals have now been replaced by digital signals in many applications and in the future, we expect digital signals to gain more popularity.

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