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COMPUTER HARDWARE 107
business life, every computer is hooked up to the network in the office. The network,
as it applies to a computer, looks just like a single cable that hooks into the back of the
computer. The computer software knows how to talk to the other computers on the net-
work and can use the wire to do so. We will discuss just how this occurs in the chapter
on communications. The commonly used communication links (between computers)
used in network communication are the following:
10/100BaseT A single cable attaches to the back of the computer to provide
10/100BT connectivity. The cable may look like a phone cable or it may be coax-
ial like a cable TV cable. It may well use the Ethernet signaling voltages and pro-
tocols, and it probably is directly connected to a switchbox in a back room full of
server computers. It’s the single most popular way of connecting computers
together and would be a good choice for the robot. Most computer boards that are
purchased off-the-shelf have a network connector on board, but beware; this type
of communication system requires a sizeable amount of software to support it. If
the robot needs such a communication link (and connector), make sure the robot’s
computer will include the proper operating and network stack software. We’ll dis-
cuss this further later.
A 10BT interface has a raw bandwidth of 1.25 MBps but generally cannot sup-
port more than 75 percent of that. The 100BT is 10 times faster. Many computers
support both interfaces. A 1000BT interface is 10 times faster again, supporting
a bandwidth of 125 MBps. Don’t forget to derate this number for practical pur-
poses. However, at such speeds, many computers cannot even keep up with a
1000BT interface; high-speed, 32-bit systems are needed. Remember, the robot’s
computer system will only be as fast as its weakest link. Here are a couple of web
sites about the type of wires needed for such communication links:
www.linksys.com/faqs/default.asp?fqid=18
www.zytrax.com/tech/layer_1/cables/tech_lan.htm
Wireless (RF) It’s not unlikely that the robot will need to be mobile. Assuming
that’s the case, having a local area network (LAN) wire plugged into the wall is
impractical (and not cool). Designers long ago freed the owners of portable PCs from
such wiring tethers with the introduction of a few wireless protocols. The most pop-
ular is 802.11, which comes in various versions, the most prevalent of which is
802.11b. It boasts speeds of up to 1.3 MBps, comparable to the wired 10BT standard.
If we can restrict the communication needs of the robot to a fraction of that band-
width, then 802.11b might make an excellent choice for external communications.
Just be aware that an RF communication link is much more prone to errors than a
wired link. Motors, computers, lights, radio stations, and even the stars all put out
interference that can quickly corrupt a well-designed, standard RF communication