PC Hardware A Beginner’s Guide

Chapter 18: Keyboards, Mice, and Pointing Devices^461

Contact Keyswitches Contact keyswitches require two parts of the switch to make con-
tact in order to complete a circuit. There are three types of contact keyswitches used in
PC keyboards:

 Mechanical contact keyswitch A very simple switch in which two metal

contacts are brought into contact or a metal plunger is pressed against contacts

on a circuit board when the switch is pressed. This type of switch is not

common on current keyboards.

 Foam and foil contact keyswitch This keyswitch is made up of a plunger that

is connected to a foam pad that has a piece of foil on its underside. A circuit

board (which provides the keyswitch grid) with a pair of copper contacts for

each keyswitch sits underneath the keyswitches. When a key is pressed, the

foam pad is pressed down and the foil contacts the contacts, completing the

Character Hexadecimal Decimal

SPACE 20 32

!2 133

”2 234

03048

13149

23250

=3D6 1

>3E6 2

?3F6 3

A4 165

B4 266

C4 367

H4 872

I4 973

J4A7 4

a6 197

b6 298

c6 399

Table 18-3. A Sampling of ASCII Codes