input and output devices

input and output devices

1. scanner

   • 2d scanners
     • place the document onto a glass panel
       • a bright xenon lamp lights up the document
         • the scan head then moves across the document. this will scan it all and produce an image which is sent to a lens using mirrors
           • the image then falls onto a CCD (charge couple devices)
             • the CCD is made up of thousands of pixels. when light hits the pixels they create an electric chage
               • the item you were scanning is now put into electronic form.
     • uses
       • in an airport
         • the passport photo is used as a reference
           • the person then gets an image taken of themselves
             • the computer then scans both images and compares things like:
               • distance between eyes
                 • width of nose
                   • shape of cheek bones
                     • length of jawline
                       • shape of the eyebrows
                         • these are then cross referenced with each other and if they get a match the person is allowed through airport security
     • how they work:
   • advantages
     • fast
       • simple
         • relatively cheap
   • disadvantages
     • bad quality
       • can't edit

2. 3d scanners

   • 3d scanners work by using 3 co-ordinates.
     • an x y and z co-ordinate
       • these stand for length width and depth
         • the scanner takes an image at several points along these co-ordiante's
           • an image which represents the object is formed
             • this image is then interpreted by the computer to make 3d model of the object
   • applications
     • CAD (compute aided design)
       • these images are then used by architects or other designers for things such as
         • 3d printing
     • medical applications
       • 3d scanners can be used in medical applications but they have different ways of doing it
         • for example x rays use computer tomography (what i outlined)
           • but MRI scannes use radio frequencies (MRI actually stand for magnetic resonance imaging)
             • SPECT scanners use gamma rays (singel photon emiision computed tomography.
       • all of these work by taking slices of the thing which is being scanned and the creating a 3d image out of it.

3. barcode scanners

   • barcode scanners are used in supermarkets mainly to keep track of how much stock of 1 item there is left
     • these use 2d scanning to read bars which represent numbers.
       • each number is split up into 7 bars. this is why there are black lines on a barcode
         • these represent the USP binary number for the number
           • the light and dark bars represent different numbers. for example the number 5 would be LDDLLLD
             • the light bars represent 0 and the dark bars represent 1
               • for example the number 1 would be represented as 0011001
           • the barcodes are also split up into two sides with three numbers on each side
             • this enables them to be scanned from any direction and orientation
   • whenever a barcode is scanned it sends a signal to the stock interface saying that there is 1 less of this item. when the number of items drops below a certain amount it automatically orders more stock
   • disadvantages
     • limited number of barcodes
       • need a full system in tact
   • advantages
     • fast
       • easy
         • simple

4. QR codes (quick response codes

   • a qr code is a matrix of lots of different black dots which could contain a message or a url
     • QR codes can hold over 7000 digits this gives a much larger scope for information storage
       • as they can be scanned anywhere they are ideal for advertising where you could just scan the code whilst on a train or walking around a city
         • these can also hold urls for a companies website or a phone number

5. digital cameras

   • Digital cameras have replaced the traditional film cameras. this is becuase the film cameras were very expensive to use and you didn't know what the picture would look like until you had got it developed. but using digital cameras they will scan the light image in front of them and then interpret the image and display it on the screen

6. keyboards and pointing devices

   • keyboards are used mainly for data entry
     • each character has an ASCII value that the computer then displays at the character on screen
       • these are the easiest way to enter text into a computer but people can develop injures over time
   • the mouse is the most common pointing device and comes in various forms
     • tracker ball. this is the most traditional type where it is connected to you computer through a usb port
       • LED these use red LED's to detect movement and change the position of the mouse depending one how you x-y value has changed

7. microphones

   • microphones work using vibrations. when a vibration enters the microphone the diaphragm moves. this then gets converted into binary and is interpreted by the computer.
     • this system is also used for speech recognition
       • for example when the word "hut"is said the computer recognises it as the first two letters and then works out hte rest of it. for example it would first hear sound h
         • after it hears this it will try to guess the word. for example it would first thing "hang" and after it would hear the "uh" sound it wuld think hung and after it hear the "t sount it will thing "hunt","hurt" and then recognisse "hut"

8. touchscreens

   • types of touchscreens
     • capacitive
       • a capacitive touchscreen use many layers of glass which act as capacitors that create electric field between the layers of glass
         • when the top layer of glass is touched the current changes. this will then be made interpreted and given different co-ordinate's depending where touched
       • benefits
         • medium cost
           • good visibility in sunlight
             • multi-touch capability
               • very durable screen
       • disadvantages
         • only allows use for bare fingers
           • strong screens
     • infra red (heat and optical)
       • heat- sensitive
         • uses glass as screen
           • needs warm object
       • opticial
         • uses glass as screen
           • uses sensors in a grid to find out where you are touching
       • disadvantages
         • its expensive
           • only allows bear fingers
             • kay visibility in strong sunlight
       • allows multi- touch capabilites
         • good durability
     • resisistive
       • uses an upper layer of plastic and a lower layer of glass
         • wehn the top layer touches the bottom layer it creates a circuit
           • signals are sent which determine where the screen is touched

9. output devices

   • whiteboards
     • whiteboards combine digital projectors and touchscreens
       • things can be written on the touchscreen and stored for later use
   • inkjet printers
     • inkjet printers uses nozzles which spray ink on the paper
       • a stepper motor on a belt moves the nozzle along to where its supposed to go
         • paper gets fed through a tray to where its supposed to go
           • types of nozzles
             • thermal bubble
               • resistors create heat which makes the ink vaporise. this makes the ink to form a tiny bubble. the bubble expands, some of the ink is ejected from the print head onto the paper. this is repeated until it is finished
             • piezoelectric
               • there is a crystal located at the back of a reservoir. the crystal is given a tiny electric charge which makes it vibrate. this forces the ink to be ejected onto the paper
   • laser printers
     • use dry ink powder instead of liquid ink
     • use a laser to charge the paper in different parts which the ink then sticks to
     • they print the whole page instead of one line at a time
   • 3d printers
     • 3d printers use a 3d computer model to make a real life model
       • they are built up layer by layer using a heated plastic filament
         • there are two types of 3d printing
           • direct
             • the print head moves left to right but also up and down
           • binder
             • binder 3d printers use 2 passes 1 for spraying a glue and another one for setting the filament
   • loudspeakers/ headphones
     • sound is produced from a computer by passing the data through a digital to analogue converter
       • this is a DAC
         • how fast the DAC can work is the sampling rate
           • if the DAC is 16 bit then it can accept numbers between 32767 and -32768
             • if a piece of music is sampled 44100 times a secondand each sample is 16 bits and it was in stereo the calculation would be 44100x2x16
   • led and lcd screens
     • lcd monitors
       • lcd screens use liquid crystal diodes. these tiny diodes are grouped together in 3's or 4's these are known as pixels
         • these are now backlite with led's but they used to be lit with a CCFL (cold cathode fluorescent lamp)
           • the CCFL uses two fluorescent tube behind a lcd screen and this is what provides a light source
             • when led's are used, a matrix of tiny LED's light up the screen.
               • LCD screens don't emit any light of there own so they need some form of backlighting
                 • new types of leds are emerging called OLED's
                   • these are organic leds which are semi conductors and are also very flexible
                     • these films are sandwiched between two electrodes one is a metallic cathode and another is a glass anode. when an electric field is applied to these electrodes they give off light
   • light projectors
     • there are two types of projectors
       • LCD projectors
         • this is an older technology than DLP
           • they fire a high intensity beam of light through an lcd display and then on to an a screen
       • digital light projectors
         • DLP's use millions of small mirrors on a DLP chip. this is key to how it works
           • the mirrors have two positions. on and off. in the on position they tilt towards the light source. when they are off they tilt away from the light source
             • these mirrors can turn on and off several thousand times a second.
               • these produce different shades of gray also known as grayscale
                 • using dlp technology it will interperate the grayscale as colours