Hardware Reference
In-Depth Information
Figure 15.2. A typical mechanical switch used in older NMB Technologies keyboards. As the key
is pressed, the switch pushes down on the contacts to make the connection.
Mechanical switches are durable, usually have self-cleaning contacts, and are normally rated for 20
million keystrokes (which is second only to the capacitive switch in longevity). They also offer
excellent tactile feedback.
Despite the tactile feedback and durability provided by mechanical keyswitch keyboards, they have
become much less popular than membrane keyboards (discussed later in this chapter). In addition,
many companies that produce keyboards that employ mechanical keyswitches either use them for only
a few of their high-priced models or have phased out their mechanical keyswitch models entirely.
With the price of keyboards nose-diving along with other traditional devices, such as mice and
drives, the pressure on keyboard makers to cut costs has led many of them to abandon or deemphasize
mechanical-keyswitch designs in favor of the less expensive membrane keyswitch.
The Alps Electric mechanical keyswitch is used by many of the vendors who produce mechanical-
switch keyboards, including Alps Electric. Other vendors who use mechanical keyswitches for some
of their keyboard models include Adesso, Inc. (
www.adesso.com
)
, Avant Prime, and Stellar
(revivals of the classic Northgate keyboards are available from Ergonomic Resources;
www.ergonomicsmadeeasy.com
)
, Kinesis (
www.kinesis-ergo.com
), and SIIG (
www.siig.com
).
Many of these vendors sell through the OEM market, so you must look carefully at the detailed
specifications for the keyboard to see whether it is a mechanical keyswitch model.
Foam Element Switches
Foam element mechanical switches were a popular design in some older keyboards. Most of the
older PC keyboards, including models made by Key Tronic and many others, used this technology.
These switches are characterized by a foam element with an electrical contact on the bottom. This
foam element is mounted on the bottom of a plunger that is attached to the key (see
Figure 15.3
)
.
Figure 15.3. Typical foam element mechanical keyswitch.
When the switch is pressed, a foil conductor on the bottom of the foam element closes a circuit on the
printed circuit board below. A return spring pushes the key back up when the pressure is released.
The foam dampens the contact, helping to prevent bounce, but it gives these keyboards a “mushy”
feel. The big problem with this type of keyswitch design is that little tactile feedback often exists.
These types of keyboards send a clicking sound to the system speaker to signify that contact has been
