Keyboard

One of the best basic PC components, which is the primary input device. Key board was available in PC’s since the introduction of original IBM PC. There are several standards available for key board in the industry.

• 101-key Enhanced keyboard
• 104-key windows keyboard
• 83-key PC and XT keyboard (obsolete) 
• 84-key AT keyboard

Keyboard technology

There are several technologies used to manufacturer keyboard. These technologies normally refer to the method how the keys are designed in the keyboard. Several technologies are as follows.

• Mechanical keyboard

As the key is pressed, the switch pushes down one the contact to create the connection.

• Foam element keyboard

When the switch is pressed, a foil conductor on the bottom of the foam element closes a circuit on the printed circuit below. A return spring pushes the key back up when the pressure is released.

• Membrane keyboard

Instead of the spring you get in a mechanical keyboard, these switches use a rubber dome that has a carbon button contact on the underside. As you press a key, a key plunger presses the rubber dome, causing the carbon button to make contact between the circuit board traces below.

• Capacitive keyboard

When the key is pressed, the plunger moves the top plate in relation to the fixed bottom plate. As the top plate moves, the capacitance between the two plate changes. The comparator circuitry in the keyboard detects this change.

• Keyboard interfaces

There are several keyboard interfaces invented so far. Following figures show the physical layout and pinouts of keyboard connectors and ports in various standards.