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Chapter 18
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Input Devices
Because of the problems with IR devices shown in Figure 18.15, almost all vendors of wireless input
devices now use radio waves (RF) for transmission between the device and transceiver. RF-based wireless devices have no line-of-sight problems, but most have a limited range of about 6 ft. from the
transmitter (see Figure 18.16).
1
A
2
2
B
6 ft.
Obstructive
object
2
2
A. Acceptable angle for receiving transmissions (360)
B. RF transceiver
1. Mouse can’t connect (out of range)
2. Mouse with connection to RF transceiver
Figure 18.16 A wireless mouse using RF must be within range of the transceiver, but unlike IR-based
wireless mice, the angle of the mouse to the transceiver doesn’t matter and radio signals can’t be blocked by
books, paper, or other obstacles.
Although RF overcomes line-of-sight issues that can cripple an IR mouse, early versions of RF products
had a high potential for interference from other devices and from other devices in use in the same
room because of a limited range of channels. For example, early Logitech wireless MouseMan products required the user to manually select the channel used by the transceiver and mouse. If more than
six users in a small room had wireless devices, interference was practically inevitable and user error
could lead to a user’s mouse movements showing up on the wrong computer screen.
Fortunately, improvements in frequency bands used and automatic tuning have enabled all users of a particular type of device to avoid interference with other electronic devices or with each other. For example,
Logitech’s current line of wireless products uses its patented Palomar technology. Although the 27MHz
frequency used by Palomar has become a de facto standard for most recent wireless input devices (it’s also
used by Microsoft and IBM for their wireless products), Logitech allows users to enable a digital security
feature that uses one of more than 4,000 unique codes to prevent accidentally activating another computer with a wireless device or signal snooping by another user. Most vendors use similar technology but
might use a much smaller number of codes. The range of 27MHz RF devices is short—about 6 ft.—but the
transmitter can be located behind the computer or under the desk without loss of signal.
Although most wireless products use proprietary radio transceivers, the Bluetooth wireless standard
can now be used by some keyboards and mice, such as Microsoft’s pioneering Wireless Optical
Desktop mouse and keyboard bundle or the Wireless IntelliMouse Explorer for Bluetooth. Logitech
also offers a Bluetooth-enabled input device: its Cordless Presenter handheld pointing device.
Bluetooth-enabled devices have an effective range of up to 30 ft. and might be compatible with other
brands of devices that are also Bluetooth enabled.