3.2 (A) Input Devices Flashcards
What is a barcode
a series of dark and light parallel lines of varying thickness
Process of scanning a barcode
Read by a laser or led light source
Light is reflected of the barcode - the white lines reflect more light compared to the black lights
The reflected light is read by sensors
A pattern is generated by the light that is reflected which is converted into digital data
What happens after the barcode is read (supermarket)
The barcode is looked up in stock database
When the barcode number is found, the stock item record is looked up
The price and other stock item details are sent back to the checkout or the POS
the number of stock items in the record is reduced by 1 each time the barcode is read
this new value for number of stock is written back to the stock item record
the number of stock items is compared to the re-order level; if it is less than or equal to this value, more stock items are automatically ordered
once an order for more stock items is generated, a flag is added to the record to stop re-ordering every time the stock item barcode is read
when new stock items arrive, the stock levels are updated in the database.
What is a key field
how does it relate to a barcode
the field that uniquely identifies a record in a file
barcode acts as a key field for items in a supermarket
What is the POS
point of sales terminal
Advantages of barcodes (managers)
Automatic stock control
More up-to-date sales information and sales trends
Much faster and easier to change prices on stock items
Advantages of barcodes (customer)
Faster checkout queues
Errors in billing are reduced
An itemized bill is given to the customer
What is a QR code
a matrix of dark and light squares which represent data
Full form of QR
Quick Response
How can a QR code be read
QR code apps and smart phone cameras
Common uses of QR codes
Advertising
Restaurant menus
Storing boarding passes of flights and trains
How a QR code is read
Point the phone camera towards the QR code
The app will process the image of the QR code, converting the squares to readable data
The data is then read and the user is directed to the website, phone app, or the data stored in the qr code is downloaded on the user’s phone.
Advantages of QR code compared to Bar code
More information
Few errors - QR Codes have a built in error checking systems. This helps guard against badly printed, damaged QR codes
Easy to read - don’t need a laser or an led light source
Disadvantages of QR codes
Can be used to transfer malicious codes. It is very easy to embed malicious code into a QR code. This code could be a virus, etc.
What is the process of transferring malicious codes through a QR code called
Attaging
What is a Frame QR code
a type of QR code that includes a space for advertising
What happens when a photo is taken (camera)
Light passes through the lens onto a light sensitive cell which converts light into electricity
Each tiny sensor is called a pixel
The image is converted to tiny electric charge which is then passed through an ADC to form a digital image array
The ADC then converts the electric charge from each pixel to levels of brightness
Finally, apart from brightness, the sensors also measure colour which produces another binary pattern
What is a CCD (Cameras) - full form and function
Charged Couple Devices - a light sensitive cell made up of millions of tiny sensors acting as photodiodes. Converts light into electricity
What is an ADC (full form and function)
Analogue to digital converter – a device that converts analogue data into a form understood by a computer
X-bit adc gives how many levels of brightness
2^x diff levels of brightness
What colour system do most cameras use
24-bit RGB Colour system - 3 primary colours, each get 8 bits.
What does the number of pixels in the picture determine
size of the file used to store the photograph
What does the quality of the image (camera) depend on
Recording device (how good the camera lens is and how good the sensor array is)
Number of pixels used (the more pixels used, the better the image)
Levels of light and how the image is stored (JPEG, raw file, png, etc)
What is a DAC (full form and def)
Digital to analogue converter - device that converts digital data into electric currents
What is a virtual keyboard
an onscreen keyboard which uses the features of the touch screen to emulate a physical keyboard
How does an ergonomic keyboard tackle RSI
these have the keys arranged differently
They are also designed to give more support to the wrists and hands when doing a lot of typing.
What is RSI (full form and def)
repetitive strain injury - pain felt in the muscles,
nerves and tendons caused by a repetitive action (for
example
How does a computer recognize the letters being pressed on the keyboard
There is a membrane or circuit board at the base of the keys
When the key is pressed the circuit is completed
The CPU in the computer can then determine which key has been pressed by referring to an index file to identify which character the key press represents
Each character on a keyboard has a corresponding ASCII value
What does a microphone do
Converts sound waves into an electric current. The current is then converted to a digital format so that the computer can process/store it
How does the microphone work
When sound is created, it causes the air to vibrate.
The diaphragm in the microphone picks up the air vibrations and begins to vibrate itself
A copper coil is wrapped around the cone which is connected to the diaphragm. When the diaphragm vibrates, the cone moves in and out causing the copper coil to move backwards and words
The motion of the coil allows it to cut through the magnetic field of the permanent magnet, which induces a current
This current is then amplified or sent to a recording device
What is the nature of the current gen by the microphone
analogue
What is an optical mouse
a pointing device that uses a red LED to track the movement of the device and then relays its coordinates to a computer
What is a pointing device
an input device that allows the user to control the movement of an onscreen cursor or to allow onscreen selection by clicking a button on the device
How many images per second does an optical mouse take
1500
What is a CMOS (full form and func)
complementary metal oxide semiconductor - a chip that generates an electric current when light falls on its surface
What is a DSP (optical mouse)
digital signal processor - a processor that calculates, the coordinates of a pointing device based on the pulses of electricity received
How does an optical mouse work
Red light is bounced off the surface
Reflection is picked up by the CSMO
CSMO generates electric pulses to represent the reflected red light
Pulses sent to a DSP
The DSP works out the coordinates of the mouse based on the changing image patterns as it is moved about on the surface
Computer reflects the movement on screen according to the coordinates sent by the mouse.
Why an optical mouse is better than a mechanical mouse
No moving parts - more durable
Dirt can’t get trapped in any of the mechanical components
No special surfaces are required
Advantages of wired connections over Bluetooth and wireless (mouse)
No signal loss - consistent pathway
Cheaper to operate - no need to buy batteries over and over again
What is a 2D scanner
Most common form of scanners that are used to input hard copy (paper) documents
How a 2D scanner works
Cover is raised, paper is placed on the glass, cover is closed
A bright light illuminates the document using a xenon lamp or LED that produces a bright white light
Scan head moves across the document, to scan the full document.
An image of the document is produced - is then sent to a lens using a series of mirrors.
The lens focuses the document image.
The focused image falls onto a CCD, converts light to electric current which converts it into an electronic form
Software produces a digital image from electronic form
What is an OCR (full form and function)
Optical character recognition - Technology that can convert hard copy text or images into a digital format such as a text file that is to be stored in a computer memory
What is a 3D scanner
Scan solid objects and produce a three-dimensional image.
Take images on several different points along the X, Y and Z coordinates.
Where can the images from a 3D scanner be used to design and create
CAD - computer aided design which is a software used to create drawings
What is a application of a 3D scanner
Computed tomographic scanners.
What does a CT scanner do
used to create a 3D image of a solid object
How does a CT scanner work
uses tomography technology, builds up an image of the solid object through a series of very thin ‘slices’.
What is a touchscreen
Allows the user to select or
manipulate a screen image using the touch of a finger or stylus
3 Types of touchscreen
resistive
Capacitive
Infrared
What is a capacitive screen made out of
Composed of layers of glass, a transparent electrode, and a glass substrate.
How does a capacitive screen work
Human skin is a conductor of electricity, when bare fingers touch the screen, the electrostatic field of the conductive layer is changed.
The installed microcontroller is able to calculate where this change took place and hence determine the coordinates of the point of touching.
Two types of capacitive screens
Surface
Projective
How does a surface capacitive screen work
sensors are placed at the corners of a screen.
Small voltages are also applied at the corners of the screen creating an electric field finger touching the screen surface will draw current from each corner
reducing the capacitance.
A microcontroller measures the decrease in capacitance and hence determines the point where the finger touched the screen.
How does a projective capacitive screen work
The transparent conductive layer is now in the form of an X-Y matrix pattern.
This creates a three dimensional (3D) electrostatic field. When a finger touches the screen, it disturbs the 3D electrostatic field allowing a microcontroller to determine the coordinates of the point of contact.
Surfaces that can control a surface capacitive screen
bare fingers
stylus
surfaces that can control a projective capacitive screen
bare fingers
stylus
thin surgical or cotton gloves
What other facilities does a projective capacitive screen allow for
Multi-touch
Advantages of capacitive screens compared to others
Better img quality comp to resistive
Durable
Projective allow multi touch
Disadvantages of capacititive screens comapred to others
Surface capacitive screens only work with bare fingers or stylus
This screen is sensitive to electromagnetic radiation
What is an infrared touch screen
Infrared touch screens use a glass screen with an array of sensors and infrared transmitters
How does an infrared touch screen work
The sensors detect the infrared radiation.
If any of the infrared beams are broken (for example, with a finger touching the screen), the infrared radiation reaching the sensors is reduced.
The sensor readings are sent to a microcontroller that
calculates where the screen was touched
Advantages of infrared touch screens comp to others
Multi-touch
good durability
operability isn’t affected by a scratched or cracked screen
Disadv of infrared touch screens comp to others
Screen is sensitive to water and moisture
Accidental activation can take place if beams are broken by any other objects or are disturbed in someway.
Could be sensitive to light interferance
What is a resistive touch screen
made up of two layers of electrically resistive material with a voltage applied across them
What is the upper layer of a resistive touch layer made of
made of flexible polyethylene (a type of polymer) with a resistive coating on one side
What is the lower layer of a resistive touch layer made of
The bottom layer is made of glass also with a resistive coating (usually indium tin oxide) on one side
How does a resisitive screen work
These two layers are separated by air or an inert gas (such as argon).
When the top polyethylene surface is touched, the two layers make contact.
Since both layers are coated in a resistive material a circuit is now completed which results in a flow of electricity.
The point of contact is detected where there was a change in voltage.
Adv of resistive touch screens comp to others
Good resistance to dust and water
Can be used by bare fingers, stylus and gloved hands
Disadv of resisitive touch screens comp to others
Low touch sensitivity
Doesn’t allow multi-touch
Poor visibility in strong sunlight
Vulnerable to scratches on the screen
