There are many different types of inputs and outputs that can be interfaced to a computer which include devices such as monitors, webcams, scanners, mice, and many more. 

Another very common device missing in that list is a Keyboard. 

Is a keyboard an input or output device?

A keyboard is an input device because it takes information from the outside world (in the form of physical keystrokes from the user), and sends it to the central processing unit (CPU). 

Information is ‘inputted’ into the computer via the keyboard and is why it is an input device. 

Difference between input and output devices

There are inputs, and there are output devices that can be connected to a computer.

So, what is the difference between input and output? Let’s take a look at each of them individually to better understand the differences between them.

But, before we delve into inputs and outputs, we need to quickly cover what encompasses a computer system. 

A computer system consists of a combination of software and hardware as seen below;

• Central Processing Unit (CPU)
• Software (Operating system)
• Hardware (motherboard, graphics card, sound card, etc)
• Communication ports
• Power system 
• Memory
• Inputs 
• Outputs

What is an input device?

A computer as you might know is a machine. Computers communicate in binary (digital), that is 0’s and 1’s, which is also known as machine code. 

At the heart of any computing system is the Central Processing Unit. The CPU acts like our brain. It has the job of receiving, processing, and transmitting information. 

An input device is responsible for gathering information from the outside world and sending (‘inputting’) this information to the CPU which can then process this data as needed. 

Information in the outside world is analog (not 0’s and 1’s). But in order for the CPU to recognize data, it needs to be presented in digital form. Input devices have the task of converting analog information into digital data which the CPU can process. 

The flow of information starts from the outside world, and makes its way inward to the CPU.

Inputs that can be connected to a computer include devices such as;

• Keyboards
• Mice
• Scanners
• Joystick
• Webcam
• Microphone

What is an output device?

While input devices provide information to the CPU, output devices perform the opposite task.  The CPU sends information to an output device which will perform a particular task in the physical world.

For example, a monitor is an output device which is responsible for displaying information in a format that a human user can read and interpret. 

Other common computer outputs include;

• Monitor
• Printer
• Headphones/ Earphones
• Projector
• Speakers

The flow of information in this scenario starts at the CPU and works its way ‘out’ toward the output. 

Key differences between input and output devices

Is a keyboard an input or output device? An in depth look

So, we just learnt about the differences between an input and output device. So which category does the keyboard belong to?

A keyboard is an input device. This comes down to the fact that it receives information from the outside world (primarily through human interaction) and sends it to the CPU. For example, when you press down on a key, that information is sent to the processor which can process it accordingly.

The main way users interact with a computing system using a keyboard as an input is by using the keys. Underneath the keys are buttons which when pressed send information to the CPU. 

A keyboard consists of many keys each having their own unique purpose. There are keys for letters, numbers, symbols, and other various functions. 

Nowadays with the advent of touchscreens, a keyboard doesn’t have to be physically present. They can be displayed on the touchscreen itself. The keyboard is displayed on screen when needed and the user simply has to press the buttons on the screen. 

Can a keyboard be an output device?

The keyboard is primarily an input device, however, keyboards do include LEDs which are outputs. These LEDs are used to provide certain statuses to the user. Like when you press the caps-lock key, an LED illuminates to let you know that caps-lock is on. 

However, the keyboard still remains primarily an input device.

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However, it should not be confused with a speaker, as a speaker is able to play a variety of sounds, whereas a buzzer can play a specific tone depending on the voltage applied to it. 

Buzzers have many applications and can find themselves in alarms, electronic toys, timers and many more. 

But, is a buzzer an input or output device? The buzzer is mainly used as an output device in an electronic circuit. An output in an electronic system is where power or information leaves the system. In the case of the buzzer, power is leaving it through means of audible sound and is the main reason a buzzer is an output device.

There are instances however, where certain types of buzzers can be used as an input as well. I shall discuss these later in the article. 

Deeper look at input and output devices

Electronic systems can be very simple or very complicated. 

They can include systems inside of systems.

But, one thing common with every system is that it will have inputs, and outputs. 

So, let’s take a closer look at both input and output devices to understand better why a buzzer is an output device, but can also sometimes be used as an input device. 

Input devices

An electronic system will usually include a processor at the center of its operation.

This processor can be a Microcontroller or a Microprocessor depending on the needs, and complexity of the application.

It is responsible for ‘processing’ information.

This information can be generated internally by the processor itself, or the information can be received via Inputs.

The reason for being called an input is because information, or power is entering the system which can be best visualised by the diagram below.

An input device’s main job is reacting to changes in the  environment or physical responses by a user which could be as simple as a button press.

The processor can then deal with the information as required.

A note to be made is that embedded systems are usually where you would find a Microcontroller or Microprocessor at the processing unit. 

An input can also be part of a non-embedded system, which can be void of a microcontroller or microprocessor. 

For example, a flashlight is a simple circuit that does not include a processing unit but includes an input like a button.

There are many different types of input devices available that provide different functionalities in different circuit setups. 

Below is a list of some of the many;

• Buttons
• Switches
• Sensors
  • Temperature
  • Humidity
  • Light
  • Colour
• Microphones
• Potentiometers
• Light Dependent Resistors (LDR’s)

Below are some common applications that use these input devices;

• Computing (Mouse, Keyboard, Webcam etc)
• Mobile phones (Keypad, Capacitive touch screen)
• Automobile (buttons)
• Entertainment systems (buttons, switches, potentiometers)

Output devices

So, we have seen one half of an electronic system,where information enters it through means of power and information via physical changes in the environment also known as the Input. 

The second half of the system is an Output. 

An output can be best described as information of power leaving the system as can be visualised by the diagram below.

Once the information has been processed by the processor, it can then be sent out of the system into the real world via an output device. 

An example would be displaying information on an Liquid Crystal Display (LCD).

Just like an input, outputs can be part of non-embedded systems as well. 

Going back to the flashlight example, when the button (input) is pressed by the user, a light turns on. The light here is the output of this simple electronic system. 

Below is a list of common outputs;

• Motors
  • Servo
  • Stepper
  • Vibration 
• Buzzers
• Speakers
• Displays
• Lighting
  • Light Emitting Diodes
  • Light Bulbs
  • Electroluminescent wire 
• Printers

Below are some common applications that use these output devices;

• Audio systems (Speakers)
• Entertainment (Displays)
• Computing (Printers)
• Interior decorating (LED, Light bulbs)
• Mobile phone (Vibration Motors)

What is a buzzer?

If you ever need to add sound to your next project, the buzzer is a great device that will enable you to do so. 

The main working principle is that when a voltage is applied to a buzzer, a material within the buzzer oscillates causing a buzzing sound. 

Changing the frequency of the buzzer will change the pitch of the sound. 

There are three types of buzzer;

• Electromechanical 
• Mechanical
• Piezoelectric

The Electromechanical buzzer was the earlier of the three invented in 1831 by Joseph Henry. These were commonly used as doorbells. 

The piezoelectric buzzer is the most commonly used today. 

Why a buzzer is an output device

So, with the knowledge of what an output is, as well as what a buzzer does, we can see why a buzzer is an output device. 

A sound is produced by the buzzer based on events that might be controlled by an input or just internal conditions in the processing unit.

Example of when the buzzer responds to an input, would be a simple doorbell. When the user presses the doorbell button, the buzzer is sounded.

An example of  an internal condition is a Timer. When specific software statements are met within the processing unit, the buzzer can be triggered. 

Power (in the form of sound) is leaving the system therefore putting the buzzer in the output device category.

Common circuits where a buzzer is used as an output device

There are a couple of circuit configurations when using a buzzer as an output device.

It can either be used in a circuit with a microcontroller, or without a microcontroller. 

Below is the circuit of buzzer when used with a microcontroller

The next circuit is a buzzer used in a circuit with a microcontroller. 

When a buzzer can be used as an input device 00

While the buzzer is primarily an output device, the piezoelectric type buzzers can also be used as an input.

Inside the piezoelectric buzzer is a piezoelectric transducer disc.

As an output, voltage is applied to the piezoelectric disc which causes the disc to oscillate thereby generating sound.

The piezoelectric disc has a neat trick however. 

When a force is applied to the disc, it can generate a small voltage at its terminals, thus now making the buzzer an input device.

It can be connected to a microcontroller which has the ability to interpret these voltages via the Analog to Digital Converter.

This opens up the door to many more applications. 

Why would you want to use a buzzer as an input device?

But, there are force sensors available that perform the same function as a buzzer when used as an input device.

So, why would you want to use a buzzer as a force sensor?

The main reason being that buzzers are much cheaper than force sensors. So, being able to take them apart and use the piezoelectric disc is a much better option.

Applications of a buzzer as an output device

Below are some common applications where a buzzer is used an output device:

• Alarms
  • Burglar alarms
  • Fire alarms
  • Alarm clocks
• Timers
• Doorbells
• Electronic toys
• Electronic musical instruments

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An LDR (Light Dependent Resistor) is one of those components that has the ability to detect light levels.

But, is an LDR an input or output? The LDR is an input device which is connected to a device capable of processing such as a Microcontroller or Microprocessor. It is an input device because it provides information to the processing device. Information flows from the LDR to the microcontroller/microprocessor. 

Output devices are things the processing device sends information to or controls in one way or another. Devices like motors, Light Emitting Diodes, Speakers etc. 

Input and Outputs

To better understand why an LDR is an input, it will help to understand the basics of Inputs and Outputs. 

Inputs and Outputs are commonly used in embedded systems. The embedded system includes a processing unit (microcontroller or microprocessor), input and outputs.

A computing system is a great example of an embedded system that includes a processing unit, input and outputs. 

The inputs of the computer include the mouse, keyboard, usb drive, headphone jack etc.

Outputs include the screen, printer, speakers, etc.

Input

An input is a device that receives information from the physical world and sends it to the processing system.

In the computer system, the keyboard receives an ‘input’ from the physical world in the form of a button press. Whenever you push a button, information is sent to the processing unit that lets it know what button has been pressed.

The flow of data starts from the outside, and works its way in. 

An input can be a button/switch, or, a sensor. There are a range of sensors available capable of sensing the physical world which range from sensing temperature to light levels (like the LDR) and much more. 

Output

While an input receives information from the outside world and sends it to the processing system, an output works in reverse.

The flow of data starts in the processing unit and data is sent to the output. 

An output is a device that gets controlled by a microcontroller or microprocessor depending on circumstances (or statements) which are determined by program code. 

For example, you might write a piece of code that turns on an LED (light emitting diode) every 10 seconds.

These circumstances can also be influenced by inputs. 

Say, you want to turn on a fan every time it gets hot. A temperature sensor can sense the temperature every time it exceeds a threshold temperature and send this information to the processing unit. The processing unit can then turn on the fan.

Common outputs used in embedded systems include:

• Motors (stepper motors, servos, brushless DC motors)
• Displays (LCDs, OLED’s)
• Pumps
• Actuators

Why the LDR is an input

So, why is the LDR an input? 

The LDR is an input because it provides an embedded system with information it receives from the external world. 

It is a type of resistor whose resistance varies depending on light intensity. Lower intensity light levels generate higher resistances and vice versa.

The information that it outputs is sent to a processing device which will process it accordingly depending on the needs of the application. 

As you can see, the LDR is an input because the flow of information starts from the outside world (this case light) and works its way inward towards the processing unit via the LDR. 

Common configurations of LDR as an Input

There are two typical configurations an LDR is used as an input ; using a Micrcontroller and using an Transistor.

Configuration #1 : Using a Micrcontroller

Since the resistance of LDR varies depending on light intensity, its common configuration as an input is a voltage divider.

The purpose of a voltage divider is to scale down a voltage. When an LDR is used instead of a fixed resistor, the output voltage of the voltage divider varies as the resistance of the LDR changes.

This voltage can be used as input for a microcontroller’s ADC (analog to digital converter). The ADC can take this analog voltage and convert into a digital signal that the microcontroller can process. 

Configuration #2 : Using a transistor

Another common configuration an LDR is used as input is with a transistor and other passive components such as resistors, diodes and capacitors. This configuration does not use  a microcontroller.

A simple circuit (as seen below) uses the LDR as an input to the transistor to turn on an LED (at the output). 

Low light levels (when it’s dark) cause the LDR to increase in resistance, which causes the voltage at the base of the voltage to decrease leaving the transistor off. Due to this, no current can flow through the LED,

When light levels increase, the resistance of the LDR decreases causing a higher voltage at the base of the transistor and thus turning it on. Now a current can flow through the LED turning it on.

Can an LDR directly input to a microcontroller

As you saw above, a microcontroller has ADC inputs capable of converting analog voltages to a digital signal. 

However, it does not have any capabilities of reading resistances and since an LDR changes its resistance, it cannot be directly connected to a microcontroller. 

It will need to be used in a voltage divider configuration as mentioned above. 

Applications where an LDR is used as an input

The LDR is a versatile component used in many applications as an input. It can be found in your home, in many businesses and outside on the streets.

Below are some common LDR applications.

Alarms

The first application where an LDR is used as an input is burglar alarms. These types of alarms tend to be placed at doorways.

A laser is placed on one side of the doorway and its beam aimed at LDR on the other side of the doorway. When the beam is broken (ie. when someone walks past it) the resistance of the LDR changes and an alarm is triggered.

These types of alarms are usually found at storefronts and businesses to indicate to the people working that someone has entered.

Streetlights

Street Lights help illuminate the roads so that we can drive, and walk safely during the night.

The sun rises and sets at different times of the day. So light levels vary accordingly. Having someone manually turn on and off these street lights is very inefficient. 

LDR’s are placed in street lights and help them sense light levels so they can turn on and off automatically without the need of a human operator, thus making them more efficient. 

Solar night lights

You might have some in your garden, or might have seen them in other people’s gardens in your neighbourhood. 

Solar night lights are a great way to add some personality to your front and backyard. Just like the street lights they can also help you navigate your garden safely during the night.

They also have LDR’s that help detect light levels so they automatically turn on when light levels drop, saving you the hassle of having to turn them on manually. 

Using an LDR also helps the solar night light conserve power, as it only has to remain on when necessary. 

Smoke alarms

Yes, you read that right. Smoke alarms also use the LDR as inputs to detect when a fire is present. 

Fires pose a great threat anytime of the day or night, but even more so during the night time when you are sleeping. If a fire starts when you are sleeping you might not be aware of it until it’s too late. 

Having a smoke alarm in your house can be the difference between life and death.

A smoke alarm that uses an LDR works in similar principle to the alarms mentioned earlier. 

An LED shines a beam onto the LDR. When that beam is broken by smoke, an alarm is triggered. 

What does an LDR input into?

If an LDR is used by itself, it is quite redundant. All it is capable of doing is changing its resistance as light levels vary. 

It needs to be used as an input with a device like a microcontroller which can process and make sense of these changes in resistance. 

As you saw earlier the voltage divider is the most common configuration the LDR is found in when used as input to a microcontroller or transistor.

Can an LDR be used as an output?

The LDR’s main function is to react to changes in light levels which means it can only be useful when used as an input in the configurations using a microcontroller or transistor.

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These senses allow us to navigate and make sense (pardon the pun) of the world.

Imagine a world where you couldn’t smell or taste your favourite food, or be able to see where you are walking.

Sensors play a crucial role in an electronic system in the same way our 5 senses play a crucial role in our lives. 

They interpret real world data and send this information to a microcontroller or microprocessor for  processing.

Real world data such as temperature, rotation of a motor, force, pressure, humidity and many more. 

But, are these sensors input or output devices?

Sensors are in fact Input devices. They interpret information from the real world and convert it to a signal that can be processed (by the main processing unit). 

The flow of information starts from outside the electronic system (this case the real world) and works its way toward the main processing unit (microcontroller or microprocessor)  via the sensor. 

I shall cover more detail of the difference between Inputs and Outputs below.

Difference between and Input and Output?

In an electronic system the main processing unit is either a microcontroller or microprocessor, which executes the main program. 

Connected to the main processing unit are inputs and outputs.

To better understand whether a sensor is an Input or an Output, it will help to understand the differences between them.

Input

An input is something that reacts to external changes, and sends this information to the microcontroller for processing. The main objective of an input is sending data to a microcontroller. 

It can be something as simple as pressing a button. 

A button is considered an input because it is responding to a change in state through physical touch (either high to low, or low to high) and sending this information to be processed accordingly. 

Sensors are the most common form of inputs. 

For example, a temperature sensor reacts to changes in temperature and sends this information to the main processing unit to be further dealt with. 

Outputs

Outputs on the other hand work in the opposite direction. 

Rather than sending information to a microcontroller, a microcontroller sends information to the output which responds accordingly.

A Liquid Crystal Display (LCD) is a common output. It has the ability to display information sent to it by the main processing unit. 

Other forms of outputs are motors, speakers, buzzers, LEDs and many more. 

Below is a simple flow diagram of an electronic system with and input and output:

Sensors

So, now that we have established that sensors devices are inputs and not outputs, let’s take a closer look at the Sensor.

As I mentioned earlier, Sensors are input devices that respond and/or detect changes in the environment.

However, a sensor cannot do much by itself. It requires some sort of processing unit, like a microcontroller or microprocessor.

Working Principle

A sensor outputs a voltage depending on how it detects the physical environment.

The minimum and maximum levels of voltage depend on the electronic system as well as the maximum voltage range of  the sensor.

The change in voltage level that it outputs according to the changes in the physical environment depend on its Resolution or Sensitivity.  

So, if the output of a Light Dependent Resistor (LDR) varies by 0.5V for an increase of 1 Lux (light intensity), then its resolution is 0.5V/Lux.

This voltage gets sent to the Microcontroller’s Analog to Digital Converter. As the name suggests, this part of the microcontroller has the job of converting this analog signal into digital values.

Two primary types of Sensors

In the field of electronics, there are two types of sensors; Analog and Digital. 

Analog sensors convert physical data and output them in the form of an analog signal. This analog signal is a range of values depending on the voltages that it is working with.

For example, imagine you have a temperature sensor that has a resolution of 0.1V/Degree.

So, for every degree change you will have an increase or decrease of 0.1V. 

This gives us a nice continuous analog signal waveform. 

Digital sensors on the other hand, are limited to a certain set of possible values (these values being ones and zeros).

Due to this fact, analog sensors are much more precise than their digital counter parts. 

Different types of sensors 

Depending on the application, be sure there will be a sensor available.

Need to detect smoke, there’s a sensor for that.

Need to find the distance between you and an object, there’s a sensor for that. 

You get the point. 

Below are a list of different sensors available depending on your needs:

• Temperature Sensor
• Proximity Sensor
• Accelerometer
• IR Sensor (Infrared Sensor)
• Pressure Sensor
• Light Sensor
• Ultrasonic Sensor
• Smoke, Gas and Alcohol Sensor
• Touch Sensor
• Color Sensor
• Humidity Sensor
• Tilt Sensor
• Flow and Level Sensor

This however, is not an extensive list, but a list of the most common sensors available.

Why use sensors?

But, why use sensors to begin with? What is their real purpose?

We know that sensors can sense changes in the physical world. This benefits us in many applications.

We can all feel the temperature rise and fall, but we cannot accurately tell the precise temperature. 

Sensors however, have the ability to accurately determine the exact temperature. This helps Meteorologists predict weather patterns, so that you can plan whether to take your umbrella or not when heading out on a cloudy day.

Smoke detectors are built with smoke sensors that sound an alarm every time it senses smoke, which means there is an imminent danger of a fire.

They help us stay one step ahead of the game, letting us be proactive rather than reactive.

Since human beings only have 5 senses, electronic sensors enable us to extend our  sensing abilities.

Where are sensors used?

Sensors can be found everywhere from your home, your car, your mobile phone and many other areas and fields.

Here are some of the most common applications :

• Consumer Electronics (mobile phones, gaming systems, Computers etc)
• Automobile
• Aviation
• Medical
• Safety
• Chemical 
• Marine 
• Weather

Again, there are many more applications but these are the most common.

Conclusion

Sensors are devices that help us in daily life.

They help us sense things that we simply would not be able.

While there are many different definitions of a sensor, one thing that is certain is that they are input devices.

It is an input device that provides a signal to a processing unit depending on changes it detects in the real world.

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