Chapter 5 Input and Output Devices


Computer Systems would be very hard and cant be that usable without input or output systems.

An input device is any hardware device that sends data to a computer, allowing you to interact with and control the computer. Some examples are:

  • keyboards
  • mouse
  • sensors
  • microphones
  • digital cameras
  • touchscreens

An output device is any device used to send data from a computer to another device or use

  • inkjet printers
  • laser printers
  • loudspeakers
  • projectors
  • Headphones

Scanners are either 2 dimensional or 3 dimensional:

2D Scanners are the most common form of scanners, and they are generally used to input hard-copy (paper) documents.  The image is converted into an electronic form which can be stored in a computer. Computers equipped with OCR (Optical Character Recognition) software, allow them to scan text from the document to be converted to a text fie format.

3D printers scan solid objects and produce a three-dimensional image. Since solid objects have x,y and z coordinates, these scanners take images at several points along the three coordinates. The scanned images can be used in a computer aided design (CAD) or more recently sent to a 3D printer to produce a working model of the scanned image.

Application of 3D scanning:

Computed tomographic (CT) scanners are used to create a 3d image of a solid object. This is based on tomography technology which basically builds up an object using slices.

X rays – CT scanners

Radio frequencies MRI magnetic resonance images

Gamma rays – SPECT signal photon emission computed tomography.

Quick Response (QR) codes:

QR codes are basically another type of bar-code. This is made up of a matrix of filed in dark squares on a light background.

qr code

QR Code

This image is an example of a QR code.

Normal bar-codes can hold up around 30 digits, whereas QR codes can hold up to 7000 digits.  QR codes can easily store more information.

QR codes can be scanned easily, sice today technology is quick. Because of this, QR codes are quite famous and they save a lot of time.

Using the right application and scanner, you can read a QR code. They can contain many things such as: URL’s, ID’s, Media, etc.

A QR code is an automatic input device

Digital Cameras

Digital cameras have replaced old traditional cameras that used film to record photos. The old traditional cameras was very time consuming as you had to developed the film then printing the picture before you could see the outcome of it. Now digital cameras, with a click of a button the picture is taken and there is no wait time, it appears instantly on your phone, computer, etc. These cameras are controlled by a microprocessor which can automatically carry out the following tasks:

  • adjust the shutter speed
  • focus the image automatically
  • operate the flash automatically
  • adjust the aperture size
  • adjust the size of the image
  • remove the ‘red eye’ when the flash has been used

The photograph is captured when the light passes through the lens onto a light sensitive cell. The cell is made up of tiny elements called pixels. The nu

digital cameras.jpg

Digital Camera

mber of pixels determines the size of the file used to store the picture.










Keyboards are the most common method used for data entry. Its used as an input device on all devices. They keyboard is either connected using a USB connection or a wireless one. In tablets or phones, they keyboards are virtual or a type of touchscreen device.

Each character on the keyboard has a value (ASCII). Each key is converted into a digital signal which the computer handles and executes. Keyboards are a slow method of data entry and are also prone to errors, However its the best and easiest way of typing.

Frequent use of these devices can lead to injuries, such as Repetitive Strain Injury (RSI) in hands and wrists. Ergonomic Keyboards can help to overcome this problem, they have keys arranged differently and they give extra support to wrists and hands when doing a lot of typing.





ergonomic keyboard

Ergonomic Keyboard














Normal Keyboards


Pointing Devices: 

Pointing devices are physical devices that requires the user to ‘click’ on an icon. The mouse is still the most popular pointing device (others are tracker ball or by touchscreen) Mice can be connected to the computer via wireless connection or by a USB connection (same as keyboard) The mouse requires space for it to move around, the mouse is generally supported by a mouse pad because mat surfaces is the easiest for movement instead of something like paper which will prevent the mouse operating correctly.

An example of a pointing device is a mouse/touch-pad.


Microphones are input devices used to input sound to a computer.

Microphones are used to input sound to a computer. For example:

  • doing a voice over in a presentation
  • part of a speech recognition system
  • part of a voice recognition system

Microphones are either built into the computer or are external devices connected through the USB port or using wireless connectivity. When a microphone picks up sound, a diaphragm vibrates producing an electric signal. This signal goes to a sound card and is converted into digital values and stored in the computer.

Speech recognition is when a user uses a microphone to input words, and it outputs into a word processor or in other applications.

If the microphone is being used in a voice recognition system, the user voice can be detected and be converted into a digital wave pattern.

Both voice and speech recognition can be used in various other applications, such as, “switch on GPS”, or on Apple devices we have Siri. Key words have to be used so that the software can compare voice patterns with the computer systems limited word dictionary.


Touchscreens is the future. It is every where from phones to computers. Touchscreens are a form of input device. They allow a simple touch to activate applications or to carry out many of the functions that the pointing devices can do.

Main uses of touchscreen is in mobile phones and tablets. At present there are 3 major types of touchscreen technologies applied to mobile phone screens.

  • capacitive
  • infra-red
  • resistive


  • is made up up of layers of glass, creating electric fields between glass plates in layers.
  • when the top layer is touched, electric current changes and the co-ordinates where it was touched is determined by an on board processor


  • Medium cost of technology
  • Screen Visibility is also good in strong sunlight
  • Multi touch capability
  • The screen is durable, doesn’t shatter easily


  • Only form of input is fingers, and the latest screen screens permit a special stylus to be used


  • Heat Sensitive: uses glass as the screen
  • needs a warm object to carry out operations
  • Optical: uses glass as a screen
  • uses an array of sensors to pin point the contact of where the screen is touched from


  • Multi touch capabilities
  • Optical system can allow the use of bare fingers/gloved fingers/stylus for input
  • Good screen durability, doesn’t shatter the glass easily.


  • Expensive technology
  • Heat sensitive system is only used for bare fingers, nothing else to input from.
  • Fairly good screen visibility in strong sunlight.


  •  the top layer is made out of polyester and the bottom is glass
  • the top and bottom layer are connected via a circuit
  • signals are sent out, which are interpreted by a micro processor and does the calculation and finds the co-ordinates of where the screen was touched,


  • inexpensive technology
  • can allow the use of bare fingers/gloved fingers/stylus for input operations


  • Screen visibility is poor in strong sunlight
  • Doesn’t permit multi touch capability
  • It is vulnerable to scratch/break the screen.


Sensors are devices which read or measure physical properties . These can include temperature, pressure and so on. Real data is analogue (it’s constantly changing and doesn’t have a discrete value). However, computers cant make any sense of these physical quantities and the data needs to be converted to a digital format. This can be done by using an Analogue to Digital Converter (ADC). 

Analogue to Digital Converter (ADC).

When the computer is used to control devices, such as a motor or a valve, it is necessary to use a Digital to Analogue Converter (DAC) since these devices need analogue data to operate in many cases. Frequently, an Actuator is used in these control applications. An actuator is an electro-mechanical device such as a relay, solenoid or motor.

Digital to Analogue Converter (DAC)

Examples of sensors and applications


  • control a central heating system
  • control/monitor a chemical process
  • control/monitor the temperature in a greenhouse
  • The data can be fetched and output using an ADC
  • Uni-Directional


  • Switch street light on at night and off at day
  • monitor/control light levels in greenhouse
  • automatically switch on car headlights when dark
  • Using an ADC, the digital data can be output-ed and instructions can be given
  • Bi-Directional


  • detects intruders in a burglar alarm system
  • weigh things
  • monitor/control a process where gas pressure is crucial
  • Using an ADC, the data can be converted into digital data


  • picks up noise levels
  • detect the noise of liquids dripping in a pipe
  • Using an ADC, the data can be converted and output-ed into digital data, or using a DAC, digital data can be picked and amplified


  •  monitor/control acidity/alkalinity in the soil in a greenhouse
  • pollution/environmental monitoring in rivers

Magnetic Field:

  • any application where detection of changes in a magnetic field is required
  • used in anti-lock braking systems in motor vehicles

Sensors are used in both monitoring and controlling applications

These are how the 2 methods work:


Examples of Monitoring include:

  • checking temperature levels in a car engine
  • monitoring pollution levels in a river
  • monitoring intruders in a burglar alarm system

Examples of Control include:

  • turning street on at night and off at day
  • changing traffic lights at a road junction
  • anti lock brakes on a car when necessary
  • regulating the temperature in the air conditioning
  • regulating the environment in a greenhouse


Monitoring Applications:

Burglar Alarm System-

burglar alarm system


The burglar monitoring system carries out the following instructions:

  • The system is activated by keying in a password on a keypad
  • The infra-red sensor picks up the movement of an intruder in the building
  • The acoustic sensor picks up sounds such as footsteps or breaking glass
  • The pressure sensor picks up the weight of an intruder coming through a door or window
  • The sensor data is passed through an ADC if its in an analogue form, to produce digital data
  • The computer/microprocessor will sample the digital data coming from these sensors at a given frequency (e.g. every 5 seconds); the data is compared with the stored values
  • If any of the incoming data values are outside the acceptable range, then the computer send signals to:
  • A siren to sound the alarm, or
  • a light to start flashing
  • A DAC is used if the devices need analogue values to operate them.
  • The alarm continues to sound/lights continue to flash until the system is reset with a password

Control Applications: 

Control of a street lighting:

street lighting


The lamp is fitted with a light sensor which constantly sends data to the microprocessor. The data value from the sensor changes according to whether it is sunny, cloudy, raining or if its night time, day time, etc.

  • The light sensor sends the data to the ADC interface
  • The digital data then gets sent to the microprocessor
  • The microprocessor then samples the data every minute (or at some other frequency rate)
  • If the data from the sensor is < the value stored in memory:
  • a signal is sent from the microprocessor to the street lamp
  • and the lamp is switched on
  • The lamp stays on for 30 minutes before the sensors readings are sampled again
  • If the data from the sensor is >= value stored in the memory:
  • A signal is sent from the microprocessor to the street lamp, and lamp is switched off
  • The lamp stays switched off for 30 minutes before the sensor readings are sampled again.



A robot is an Independent device which capable of doing jobs, human cannot, reducing human error

  • The word robot was coined by a Czech novelist Karel Capek in a 1920 play titled Rossum’s Universal Robots (RUR)
  • Robota in Czech is a word for ‘worker’ or ‘servant’

What do we need the robot to do:

Moving: The robot must be able to control some set of actuators to move how and when we want it to. We must be able to reliably place the robot anywhere we want.

Sensing: The robot must be able to perceive its environment through sensors locate obstacles to avoid, and objects of interest that we want it to interact with.

Plan/Act: The robot must be able to make decisions using its processor based on its sensors and feed them to its actuators to be able to move.

What are Robots used for:

Robots can be used for many things, technology is advancing very quick. They can do jobs which humans are uncapable, or humans take too much time on, etc.

Industries Using Robots:

  • Agriculture
  • Automobile
  • Construction
  • Entertainment
  • Health care: hospitals, patient-care, surgery , research, etc.
  • Laboratories: science, engineering , etc.
  • Law enforcement: surveillance, patrol, etc.
  • Manufacturing
  • Military: demining, surveillance, attack, etc.
  • Mining, excavation, and exploration
  • Transportation: air, ground, rail, space, etc.
  • Utilities: gas, water, and electric
  • Warehouses


  • Greater flexibility, re-programmability, kinematics dexterity
  • Greater response time to inputs than humans
  • Improved product quality
  • Maximize capital intensive equipment in multiple work shifts
  • Accident reduction
  • Reduction of hazardous exposure for human workers
  • Automation less susceptible to work stoppages


  • Replacement of human labor
  • Greater unemployment
  • Significant retraining costs for both unemployed and users of new technology
  • Advertised technology does not always disclose some of the hidden disadvantages
  • Hidden costs because of the associated technology that must be purchased and integrated into a functioning cell. Typically, a functioning cell will cost 3-10 times the cost of the robot.

Sensors in Robots:

Human senses: sight, sound, touch, taste, and smell provide us vital information to function and survive

Robot sensors: measure robot configuration/condition and its environment and send such information to robot controller as electronic signals (e.g., arm position, presence of toxic gas)

Robots often need information that is beyond 5 human senses (e.g., ability to: see in the dark, detect tiny amounts of invisible radiation, measure movement that is too small or fast for the human eye to see)


  • Assembly dexterity does not match that of human beings, particularly where hand-eye coordination required.
  • Payload to robot weight ratio is poor, often less than 5%.
  • Robot structural configuration may limit joint movement.
  • Work volumes can be constrained by parts or tooling/sensors added to the robot.
  • Robot repeatability/accuracy can constrain the range of potential applications.
  • Closed architectures of modern robot control systems make it difficult to automate cells.



Sony Aibo


Welding Robot


wheeled robot

Wheeled Robot



Output Devices:

Inkjet Printers:

Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper, plastic, or other substrates. Inkjet printers are the most commonly used type of printer, and range from small inexpensive consumer models to expensive professional machines.


Inkjet printers are best for one-off photos or where only a few pages of good quality, color printing are needed; the small ink cartridges or small paper trays would not be an issue with such applications.

Laser Printers:

Laser printers differ greatly from the inkjet printers in the way they print pages. Rather than using liquid ink, they used dry powder ink to produce text and images. Laser printers are very fast and they can print a whole page in one whole go. This is far more faster and better over inkjet printers.


Laser Printers produce high quality printouts and are very fast when producing multiple copies of a document. They are used often for advertisements as well, as a large number of high-quality flyers or poster are used. Laser printers have two advantages over inkjet: they have large toner cartridges and large paper trays.



Projecters are used to project computer output onto larger screens or even onto interactive whiteboards. They are often used in presentations and in multimedia applications.

There are 2 common types of projectors:

  • Digital Light Projectors (DLP)
  • LCD Projectors

LCD Projectors:

Older technology than DLP projectors, and has a high intensity beam of light. This is how it works:

  1. Powerful white light beam is generated from a bulb or LED inside the projector
  2. The beam is sent to a group of chromatic-coated mirrors, these reflect light back at different wavelengths
  3. When the white light hits the mirrors, the reflected lights has wavelengths that correspond to red, green, and blue light components
  4. These three beams then pass through three LCD screens; these screens show the image to be projected as millions of pixels in a grey scale
  5. When the colored beams pass through the LCD screen, the colored version of the grey image emerges
  6. These images are then combined using a special prism to produce a full color image – this final image consists of millions of colors (each shade of grey in the original image produces a different shade  in each of the color images)
  7. The image passes through the projector lens onto the screen

lcd diagram


Digital Light Projectors (DLP):

In the DLP uses millions of micro mirrors in order to display a image, the amount of micro mirrors determines the resolution of the picture. When the micro mirrors are tilted towards the light source they are switched ‘on’ and when they are tilted away, they are switched ‘off’ . This creates a light or dark pixel on the screen.



Loudspeakers convert analogue voltages into sound. If the output is from a computer, the digital signals will then first be converted into analogue voltages using DAC. But if the output is from a loudspeaker, the sound will go through an ADC, and be converted into digital signals


LCD: (Liquid Crystal Display/Diode) The front layer of the monitor is made up of tiny diodes in groups (which are also known as pixels). The colors are grouped together to make the colors more vivid.

  • They reach maximum brightness much faster
  • They give a whiter light making the image more vivid
  • The brighter light improves colour definition
  • The displays can be much thinner and lighter in weight
  • LEDCs last almost indefinitely
  • They consume much less power and therefore also run much cooler.

LED: (Light Emitting Diode) LED is a  device that emits visible light when an electric current passes through it.

  • LEDs reach their maximum brightness almost immediately
  • LEDs give whiter light which sharpens the image and make the colours appear in more detail and more vividly.
  • LEDs produce a brighter light in which improves the colour definition
  • LEDs last almost indefinitely. Therefore this makes the technology more reliable and it also means a more consistent product.
  • LEDs consume very little power which means that they produce less heat as well as using less energy. Thus cutting down on the cost of electricity that is used to run the LED itself.

OLED:  OLED is a “light-emitting diode containing thin flexible sheets of an organic electric material, used for visual displays.”

Advantages of using OLED when compared to older LED technology  are:

  • They allow for very thin and very flexible screens which are very light weight
  • They produce a much brighter light than LEDs
  • They don’t require any form of backlighting
  • They allow for a much larger field of view