To Communicate with the computer system we require some kind of input device and output device. Input device is used to feed data into the computer system and output device is required by the computer to communicate the result to the user
The keyboard is most useful part of the computer. It can not be thought the computer without the keyboard. It is used in most application as an input device. The keyboard is an integral part of the computer.
One of the main component of any keyboard is the switch. These switches convert our typing action into proper signal for the keyboard interface, so that the interface will know that a key is being depressed
Different technology used to make these switches are
A membrane keyboard is multi-layer plastic or rubber assembly which is commonly used as keyboard in video game machines, calculators, medical instruments, cash register etc.
In this keyboard, two rubber or plastic sheet are used as row conductor sheet and column conductor sheet. These row and column sheet are separated by another sheet with holes at the key top positions.
When the row lines o the row conductor sheet touch the column line on the column conductor sheet, key contact is made. This is interpreted by the keyboard interface as key closure.
Various types of mechanical switches are sued to make keyboard, the basic theory behind these switches are same. In this type of switches, two metal pieces or contacts are kept in open position and moved into close position when the switch depressed.
When the switch is in normal position the contact is open, when the switch is pushed the contact closes, and this closure is sensed by the keyboard interface.
As this type of switches require physical contact for proper working, after some use these contact becomes oxidized or dirty and switch becomes problematic.
Most of the quality manufacturers provide gold plating on switch contacts to improve the switch's life span.
In this type of keys, a rubber like synthetic material is molded to form a dome like shape, the dome like rubber structure keeps the key in up position. When the key is pressed, dome collapse and a small tab of carbon or some other conductive material inside the dome completes the circuit.
Once the pressure form the keys is released, the rubber dome goes back to its normal shape, with it pushing the key into nora ml up position and breaking the contact.
One drawback of this keyboard is, by the time as the rubber loses its elasticity, the keys becomes stiff.
In the most common organization of the keyboard is the key switches are arranged in a matrix of row and columns.
This matrix organization saves a lot of complication and additional circuits required for directly connecting each key to a separate sensing circuit.
In this method, each key switch has a corresponding row and column number associated to it. When the switch is closed, the row and column sensor senses the switch closure.
The process of sensing which key is being pressed by reading the row and column values is called "Keyboard Scanning".
The word "scanning" is used here because the interfacing circuitry scans each row and column one by one to find out the key switch being pressed.
The complete process of keyboard scanning is as follows
Keyboard sends a scan code to the processor to inform about the pressing of a key on the keyboard. This scan code has nothing to do with the characters printed on top of the key switches, it completely depends on the position of the keys on the keyboard.
Once the scan code is send to the processor, it is the job of the processor to convert this scan code into some meaningful format such as ASCII code.
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