Chapter 5: Input and output devices

Input devices:

1.       Scanners:

a.       3D – These scanners scan an object along the x, y and z axes. These scanned images are then used in Computer Aided Design (CAD), or sent to a D printer to take a 3D printout. 3D scanners are used in computed tomographic (CT) scanners. These scan through very thin slices of the object by the use of x-rays, gamma rays and radio frequencies.

b.       2D – These scan the x and y axes of an object. These are used at airports and make use of OCR (Optical Character Recognition) technology. This software scans the text and automatically inputs this text into pre-existent databases. The text may be stored in the ASCII format.

2.       Barcode reader/scanner: Barcodes are a series of black and white parallel lines with varying thicknesses. The digits from 0 to 9 are represented by a unique series of lines. Normal barcodes can hold up to 30 digits.

a.       Working of a barcode:

                                                     i.     It is first read by a red LED or a red laser

                                                    ii.     Light is reflected back (dark areas do not reflect light), and hence, the dark and light areas are determined

                                                  iii.     The reflected light is read by sensors

                                                   iv.     At the laser or red LED, light is scanned across which generates a pattern which is then converted to digital data that allows the computer to understand the barcode

                                                    v.     After being scanned, the barcode is looked up in the stock database and the price and stock item details are sent to the check out (or Point of Sale terminal – POS)

                                                   vi.     The number of stock items is reduced each time the barcode is read

                                                 vii.     If the stock items are lesser or equal to a user-specified value then stocks are automatically reordered

                                                viii.     Once stock is reordered, a flag is put to stop reordering until the stock has arrived

b.       Advantages to the management

                                                     i.     Easier and faster to change prices on stock items

                                                    ii.     Better, updated sales information

                                                  iii.     No need to price every stock item on the shelves

                                                   iv.     Allows for automatic stock control

                                                    v.     Possible to analyze customer buying habits more easily by linking barcodes to loyalty cards

c.       Advantages to the customers

                                                     i.     Faster queues as staff don’t need to remember prices

                                                    ii.     Errors in charging customers are reduced

                                                  iii.     Customer is given an itemized bill

                                                   iv.     Cost savings can be passed on to the customer

                                                    v.     Better track of ‘sales-by-dates’; so food should be fresher

3.       Quick Response (QR) Code: It is made up of a matrix filled-in with dark squares on a light background. These codes can hold up to 7000 digits. These are used for redirecting devices to specific web pages after these codes are scanned. They are used in shopping malls and on public transport for advertising.

4.       Digital cameras: Modern digital cameras can link with a computer using a Universal Serial Bus (USB). The photograph is captured when light passes through the lens onto light-sensitive cells.

5.       Keyboards: used to input text. In Concept Keyboards, each key has a specific function.

6.       Pointing devices: Mouse and tracker ball are examples of a pointing device.

7.       Microphones:  These are used to input sound into a computer. These are also used in sound recognition.

8.        Touch-screens: These allow users to interact with devices just by touching the screen. There are 3 types of touch screens: capacitive, infrared and resistive.

a.       Capacitive: Made up of layers of glass that act like a capacitor creating electric fields between layers. Touch is sensed when electric field changes due to a touch. This allows multi-touch, is visible in sunlight and is a medium-cost technology. However, it only senses touch from bare fingers (latest screens permit a stylus too). There is a good durability.

b.       Infrared: These need a warm object to sense a touch in the glass screen – this is in a heat-sensitive system. In an optical system, it uses an array of sensors like a grid on the screen where touch is categorized into the coordinates of the sensors on the grid. There is multi-touch and allows touch from gloved fingers too. There is a good durability. However, it is an expensive technology. Heat-sensitive doesn’t allow for gloved fingers to touch, and the visibility in sunlight is mediocre.

c.       Resistive: There is a layer of polyester on the top layer of the screen and a bottom layer of glass. When the top layer is touched it completes a circuit with the bottom layer and touches are sensed. Microprocessors determine the coordinates of the touch. It is cheap and senses touches with gloved fingers too. However, screen visibility is poor in sunlight and there is no multi-touch and the screen durability is mediocre – it is vulnerable to scratches and the screen wears out through time).

Sensor: This is a device that detects or measures a physical property and records, indicates, or otherwise responds to it. ADC is analogue-to-digital converter and DAC is vice versa.  An actuator is a type of motor that is responsible for moving or controlling a mechanism or system (example: relay, solenoid, etc.). A system can be developed using sensors, converters, a feedback cycle and a control system.

Output devices:

1.       Printers:

a.       Inkjet: This is made up of a print head which consists of nozzles that spray ink, an ink cartridge hat contains ink, a stepper motor which moves the print head from side-to-side and a paper feed which feeds the printer with pages as required. These are slower and cheaper than laser printers and are good for small printouts.

b.       Laser: Use dry-powder and make use of static electricity to print and they print the page in one go. They are fast, produce high-quality printouts, don’t run out of ink halfway and can carry out big printing tasks.

c.       3D printers: These are used in CAD (Computer-Aided Design), prosthetic limbs (artificial arms and legs) manufacturing, items to allow precise reconstructive surgery, in aerospace where 3D parts of space crafts are manufactured, in fashion and art and in making parts that are no longer manufactured in industries.

                                                     i.     Additive manufacturing: In this method, an object is created layer-by-layer.

                                                    ii.     Subtractive manufacturing: In this method, breaking down a block to the shape of the desired object printout creates an object. This is an older method.

                                                  iii.     Direct printing uses inkjet technology: a printer head moves left and right and up and down too to build up layers of the object.

                                                   iv.     Binder 3D printing is similar to direct 3D printing but in this method there are two passes: the first pass sprays a powder while the second pass sprays a glue to form a solid layer.

2.       3D Cutters: These are lasers that cut through objects made of glass, crystal, metal, polymer or wood by detecting it across the x-y-z axes. These cutters can produce very intricate designs.

3.       Loudspeakers: These consist of a DAC that converts digital signals to sound signals that are amplified by a connected amplifier after which it goes to a speaker.

4.       Monitors:

a.       LCD: Liquid Crystal Display/Diode. Modern monitors are backlit using LED monitors.

b.       LED: Light Emitting Diode. These reach maximum brightness almost immediately.

c.       OLED: Organic Light Emitting Diode. These are very flexible, which allows for very thin screens. These also have a brighter light than LEDs.

5.       Light Projectors:

a.       Digital Light Projector (DLP):

                                                     i.     These use millions of micro mirrors, which when tilted towards the light source are considered on and when tilted away, off. These mirrors can switch on and off thousand times a second.

                                                    ii.     A bright light source passes through a color filter on its way to the DLP chip. The white light is then split into 3 primary colors: red, green and blue.

b.       LCD Projectors: This is an older technology than DLPs.

                                                     i.     A powerful beam of light is generated from an LED inside the projector body.

                                                    ii.     This light is then sent to chromatic-coated mirrors which reflect the light back at different wavelengths

                                                  iii.     The reflected light has wavelengths corresponding to red, green and blue light components.

                                                   iv.     These 3 colors pass through LCD screens, and then these rays are combined using a prism to produce a full color image.