keyboards
Most keyboards have 80-110 keys,including:The typing keys include the letters of the alphabet,symbols,and the numbers,generally laid out in the same pattern used for typewriters.
1 control keys:provide cursor and screen control,including Home,End,Insert,Delete,Page Up,Page Down,Ctrl,Alt,and Esc;
2 Function keys:Applications and operating systems can assign specific commands to the function keys.
3 The numeric keypad,a set of 17 keys,is a more recent addition to the computer keyboard as the use of computers in business environments increased.
A large part of a keyboard is the key matrix and keyboard switches underneath the keys.A keyboard also has it own processor and circuitry that controls information to and from the computer
When a key is pressed,it presses a switch,completing the circuit and allowing a tiny amount of current to flow through.When the processor in the keyboard finds a circuit that is closed,it compares the location of that circuit on the key matrix to character map in its read-only memory.
A character map is basically a comparison chart or a lookup table,It tells the processor the position of each key in the matrix and what each keystroke or combination of keystrokes represents.
A computer can also use separate character maps,overrinding the one found in the keyboard.This can be useful to typing in a language other than English.
In addition,operating systems and applications have keyboard accessibility settings that let people change their keyboard's behavior to adapt to disabilities.
Keyboard switches use a variety of technologies:
Metal contact
Foam element
rubber dome
membrane
capacitive switch
Many keyboards connect to the computer through a cable with a PS/2 or USB connector.The cable carries power to the keyboard,and it carries signals from the deyboard back to the computer.
Wireless keyboards connect to the computer through infrared,radio frequency or Bluetooth connections.Such keyboard have a build-in transmitter,and require a receive on the computer side.either builtin or plugged in to the USB port.Since they don't have a physical connection to the computer,wireless keyboards use their own power.
When the OS is notified that there is data from the keyboard,it checks to see if the keyboard data is a system level command.if not,then the OS passes the keyboard data on to the current application.
The application determines whether the keyboard data is a command,like Alt-F,which opens the File menu in a Windows application.If the data is not a command,the application accepts it as content.if the current application does not accept keyboard data,it simply ignores the information.
1) Track-ball Mice
2) Optical Mice
Optical mouse actually uses a tiny camera to take thousands of pictures every second.Here's how the light source,the sensor and other parts of an optical mouse work together.
Most optical mice use a small,red LED as the light source.
The light bounces off almost any surface onto a CMOS sensor.
The CMOS sensor sends each image to DSP(digital signal processor) for analysis.
The DSP detects patterns in the images and examines how the patterns have moved since the previous image.
Based on the change in patterns over a sequence of images,the DSP determines the direction and distance the mouse has moved,and sends the corresponding coordinates to the computer.
The computer moves the sursor on the screen based on the coordinates received from the mouse.This happens hundreds os times each second,making the cursor appear to move very smoothly.
a number of factors affect the quality of an optical mouse:
Resolution:it is the number of pixels per inch that the optical sensor and focusing lens can see.most mice have a resolution of 400-800 dpi.Laser-baser-based optical mice designed for games can offer as high as 1600 dpi resolution.
Size of the optical sensor:sizes range from 16*16 pixels to 30*30 pixels.
Refresh rate:it is how often the sensor samples images,Rates range from 1500 to 6000 samples per second.
Image processing rate:it is a combination of the size of the optical sensor and the refresh rate,Rates range from 0.486 to 5.8 mega-pixel per second.
Maximum speed:it is the maximum speed that you can move the mouse and obtain accurate tracking.Rates range from 16 to 40 inches per second.
Motion -Based Mice
Biometric Mice.