Figure 3-1.—Examples of switches used with computers.
. Alternate-action key switches —When you
depress a key, it activates that function. Alternate-
action keys come in a couple of varieties. With one
variety, you simply depress the key to activate the
function. To deactivate the function, you depress the
key again. The second variety is the inward/outward
variety. The function is activated when the key is
latched inward and disabled when the key is unlatched
outward. Some alternate-action keys have an indicator
light telling you the function is active. These are called
indicating keys/switches. Non-indicating lamp keys are
the same as indicator keys except no indicator light
shows the function is active.
. Momentary-action/contact key switches —
Momentary-action/contact key switches operate on the
principle that depressing them one time momentarily
activates a function or sends data to the computer.
Some momentary-action/contact keys are designed so
that when you hold down the key, it repeats the function
continuously.
Also some momentary-action/contact
keys are backlit to indicate they are actuated.
Position Switches
Two types of position switches are used on
computer controlling units. They are the rotary and
thumbwheel switches.
. Rotary switches —Rotary switches usually have
several positions the operator can select by turning a
knob. The values for the positions are usually marked
on the controlling unit’s cover. The position selected
by the operator can be locked in that position until the
operator selects another position.
l Thumbwheel switches —Thumbwheel switches
are rotary position switches with alphanumeric
characters built into the switch to indicate their position
or value setting. You dial the alphanumeric settings on
the switch in a manner similar to dialing the numbers
on a thumbwheel combination lock. Each position is
locked until you select another position.
Pushbutton Switches
Pushbutton switches may or may not have
indicators.
l Pushbutton non-indicator switches —
Depressing a pushbutton non-indicator switch usually
activates a function instantaneously. On some units and
depending on the function, holding the pushbutton
down continuously will have no effect. On other units,
the function will be continuous until the pushbutton is
released.
l Pushbutton indicator switches —Pushbutton
indicator switches can be used manually to select a
function or mode, to input data to the computer, or to
indicate status automatically when under the control of
the computer’s software. Lens colors vary on
pushbutton indicator switches. Also, on some
pushbutton indicators switches, the lamp and switch are
separate. This enables you to replace either the lamp or
switch. On other pushbutton indicator switches, you
must replace the whole item; the lamp and switch are
not separate.
3-3
