Pushbutton Switches

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. 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. 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. 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