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