Input / Output Devices 

1.1 Mouse

• basics developed by Douglas C. Englebart (he won a Turing Award for it)
• most intuitive of the input devices; children will use them naturally
• supplements the keyboard by moving and pointing things on the screen
• signals: movement, double click, single click, right click.
• mechanical mouse 
  • you move mouse and the rubber mouse ball moves.
  • rollers pick up movements of ball - one to pick up back and forth movements, one up and down.
  • roller's data is encoded and is sent to the PC via the tail
  • clicking a button creates another signal to send to the PC
  • mouse ball and rollers needs frequent cleaning
• optical mouse
  • has a camera in place of the rubber ball
  • it takes thousands of 'pictures' and figures out were it is by comparing surface imperfections
  • huge benefit is that the mouse ball never gets dirty!
  • chip to do all of the processing of movement was very expensive. It is getting much cheaper.

1.2 Keyboard

• very important input device; requires special training to use it well
• mice cause some carpal tunnel, but keyboards are by far the worst cause of carpel tunnel
• many ergonomic designs of keyboards (split keyboards)
• signals: individual keys and CTRL, ALT, SHIFT combinations
• keyboard
  • pressing a key causes change in current flow
  • microprocessor picks up changes in current flow and determines which keys are pressed. passes it onto BIOS
  • BIOS takes the keyboard code and translates to a letter
  • BIOS also handles the CTRL, ALT, Caps, SHIFT keys

1.3 Touch Screen

• use finger or a special light pen to control the software
• too tiring to use for any length of time
• how it works
  • many types of screens which all essentially generate an electric current when the pen touches the screen. The sensor detects the x,y co-ordinates of the pen's location.
  • pen's position is indicated on the screen called "showing ink"
  • at the end of the pen stroke, the computer needs to interpret which letter or line it needs to record
  • the software takes the pen strokes and compares each letter to character template. The scanned images are related to actual letters or symbols. 

1.4 Scanner (marksence, barcode, page)

• eyes of the computer 
• how scanner works
  • light shines on paper, reflections of light are used to measure colours
  • page is divided into tiny pieces. scan head measures light reflected in each of areas. 
  • light (analog) is converted to digital pixel. 
  • digital data is passes back to the computer
• barcode is a small handheld scanner, page scanners are generally referred to as flatbed scanners

1.5 OCR - Optical Character Recognition

• how OCR works
  • scanner hardware is present. they pass the pixel digital data to computer
  • OCR software takes the bitmap image and compares each letter to character template. The scanned images are related to actual letters or symbols.
• many uses to it: translates written data (barcodes, books) to digital form that can be manipulated directly. 

1.6 MICR - Magnetic Ink Character Recognition

• the numbers on the bottom of a cheque are printed in magnetic ink so they are easily read by a computer's MICR machine.

1.7 LCD - Liquid Crystal Displays

• flat screen monitors and digital watches use the method of displaying data
• liquid crystals are put between two sheets of polarized glass and a grid of wires. When current is put through the wires, the crystals shift position

1.8 Voice Recognition

• useful to prevent carpel tunnel syndrome
• are special packages for most industries (doctors, lawyers...) with words that would be used by the people in the industry.
• how voice recognition works
  • you speak into a microphone. your voice is an analog sound wave.
  • the computer translates your voice into a digital sound wave and ultimately binary code.
  • it takes the binary code and attempts to figure out which word you said by matching it to a database of your speaking.
  • the computer also tries to look at groups of words to figure out if what you said is probable. "Eye live compare" is not probable but "I love computers" is.
  • the words are printed to the screen

1.9 Digital Cameras

• causing huge changes in photography industry - not as fast as predicted. Some companies are making the change away from film, some aren't.
• often used with software like Adobe Photoshop or Illustrator or Corel Paint/Draw to manipulate the image
• how a camera works
  • light enters the lens of a camera, as it does in a film camera
  • light is focused on a surface inside the camera. this surface has transistors on it that change current in portion to the light that hits them. 
  • the surface relays the information about how much light has hit each of the transistors to another device which translates the information into digital format.
  • the digit format of the picture is stored on the memory in the camera.
  • the picture is moved from the camera to another medium (PC) via a cable, or another method

1.10 Graphics Tablets

• popular with engineers and architects who must translate pen movements to computerized lines
• it is difficult to write software that can easily interpret people's messy handwriting.
• how it works
  • many types of screens which all essentially generate an electric current when the pen touches the screen. The sensor detects the x,y co-ordinates of the pen's location.
  • pen's position is indicated on the screen called "showing ink"
  • at the end of the pen stroke, the computer needs to interpret which letter or line it needs to record
  • the software takes the pen strokes and compares each letter to character template. The scanned images are related to actual letters or symbols. 

1.11 Printers

• Laser Printers produce a higher quality printout, but they are more expensive. Ink Jets tend to be the norm in the home because they are cheaper and their printout is quite a good quality.
• Laser Printers
  • reflects a laser beam on a mirror
  • electric charge builds where the laser hits the mirror, it attracts particles of toner
  • the roller turns and passes the toner to the sheet
  • the particles are heated and are fused onto the sheet
• Ink Jet Printers
  • tiny drops of ink are squirted at the pages
  • magnetic plates attract the ink to the correct configuration on the page

1.12 Plotters

• drafting tool that is run by a computer
• has multicoloured pens that draw the image on the paper
• used by some engineers and architects

2. Further Information

• How Stuff Works - the classic. Great pictures, great explanations.