is blocking the path, you must move either the obstruction or the controller to reopen the
line-of-sight. Using an IR connection, a portable PC or a PDA (personal digital assistant)
can connect to another PC, keyboard, mouse, or printer without the need for a physical
cable connection. Most IR ports (receivers) are built into the case of the PC or notebook,
but external IR receivers can be attached to the PC through a serial port or USB port.
Here are some tips for working with IR devices: Two IR devices must have a clear, unobstructed line-of-sight between them.
The devices you are trying to connect via IR must be at least six inches apart,
but not more than three feet.
The transmission pattern of the IR signal is a cone about 30 degrees wide.
Make sure the devices are oriented to one another inside the transmission cone.
Make sure there are no competing IR devices in the vicinity that may interfere
with the connection, such as a TV remote control.Radio Frequency Interfaces
Many cordless peripheral devices, especially those that are typically used in close proximity
of the PC’s system case, use radio frequency (RF) transmitters, receivers, and transceivers
(the combination of a receiver and transmitter) to send data to the PC. RF devices include
mice, keyboards, modems, and even network adapters for desktop and portable PCs.RF Keyboards and Mice
Cordless RF mice and keyboards transmit data to a base receiver that is attached to the PC
through either a serial or PS/2 connection (discussed in the next section). The operating
range of these devices, despite claims of good performance as much as 50 feet away, is more
like 6 to 10 feet. In that range, the performance of the cordless RF keyboard and mouse is as
good as a wired device. Figure 19-14 shows a cordless RF keyboard and mouse.
RF networking devices, which are covered by the IEEE 802.11 wireless networking
standardandthenewBluetoothtechnology,arediscussedinmoredetailinChapter20.PS/2 and DIN Connectors
Thetwomostpopularconnectorsforconnectingkeyboards,mice,andexternalIRandRF
receivers are the PS/2 and the 5-pin DIN connector. For more information on these two
connector types, see Chapter 18.
Nearly all mice sold today use the PS/2 connector. This connector has essentially re-
placed the DB-9 serial connector that was used in the past. Serial mice are still available,
but since newer PC systems rarely offer more than a single serial port and do include
PS/2 connectors for the keyboard and mouse, the serial mouse connector has all but dis-
appeared, except on legacy systems.Chapter 19: Ports and Connectors^499