L4 - Input and Output Devices

What is an input device

any device that allows you to pass information from the outside world into a computer system

pen type barcode readers

• contain a light source and a photo diode

• the tip of the pen is dragged across the bars

• the diode measures the light intensity and generates a waveform that is used to measure the width of the bars and spaces

• durable because they can be sealed against dust dirt and environmental hazards

• limited applications because must be in direct contact with barcode

• laser scanners are basically the same but are more applicable and have a laser beam

camera based readers

• uses a camera and image processing techniques to decode 1D or 2D barcode, printed or onscreen, damaged or poorly printed

digital cameras

• uses CCD or CMOS sensors

• includes a grid of millions of light sensors

• records binary data onto camera’s memory card

• CCD produces higher quality images than CMOS because CCD uses 100 times as much power

characteristics of RFID tags

• can be read without line of sight and from 300m

• pass stored data from tag to receiver

• has a microchip transponder and an antenna

• smallest tags are rice-sized

passive and active RFID tags

• active tags include a battery to power tag so it actively transmits a signal for a reader to pick up so they are larger

• passive tags are cheaper because they don’t have a battery and they rely on the reader emitting radio waves to provide it with electromagnetic power, then the tag becomes energised and can send data to the reader

What is an output device

take data produced by the computer and turn it into a form that humans can understand

what are LCD (light crystal display) monitors?

• groups of rgb diodes to form each pixel

• sharper, realistic, vivid image

• back-lit by LEDS

• thin screens because LEDS are small

• long lasting, low power, low heat, bright light

Describe OLED (organic LED) screens

• brighter, thinner and lighter

• plastic, flexible screen

• flexible enough to print onto clothing

• don’t require backlighting

• refresh 200 times faster than LCDS

• allow colours to be viewed from a bigger viewing angle

• water-sensitive and not long lasting

laser printers

• high quality high speed printing

• use powdered ink called toner

• used in homes, businesses and printing services

• colour laser printers are more expensive to run than b/w

• 4 cartridges (cyan, magenta, yellow, black)

• not good for photorealistic things

Inkjet Printers

• spray dots of ink onto paper to create an image

• can produce excellent photo-realistic images depending on resolution, number of cartridges, quality of paper

• slower but cheaper than laser printers

• replace cartridges recently

Dot matrix/impact printer

• a matrix of pins strike the surface of the paper through an inked ribbon to form letters

• useful when multi-part stationery

• can operate in damp and dirty environments

• noisy, slow, poor print quality

3D printers

• can produce spare parts and prototypes

• can produce car parts, med equipment and accessories (basically anything)

• can also produce guns (hmmmmm)

  • can be used when one-off items are required

multimedia projectors

can present graphics, audio, text and video on the screen interactively

computer speakers

• most PCs, smartphones etc have basic inbuilt speakers

• high quality speakers can also be bought

• they give verbal sat nav instructions, act as screen readers, send notifications

actuators

• motors that are used in conjunction with sensors to control a mechanism

• open windows, start pump, turn wheel, control devices in a smart home