Hardware Reference
In-Depth Information
In the past few years, a wide array of commer-
cial appliances has come on the market that
can connect directly to the Internet without the
aid of a personal computer. Companies like D-Link, Sony,
Axis, and others make security cameras with network
interfaces, both Ethernet and WiFi. Ceiva, eStarling, and
others make picture frames with WiFi connections to
which you can upload images from the Net. Ambient
Devices makes lamps and displays of various sorts that
connect to the Net and change their appearance based
on changes in information, such as stock market data,
weather, and other scalar quantities. Cable television
set-top boxes are computers in a small box, capable of
routing streams of audio, video, and data all at the same
time. In fact, the operating system in your set-top box
might even be a variation of the same Linux operating
system that's running on your network provider's web
hosting machine. Home alarm systems are made up of
networks of microcontrollers that talk among themselves,
with one that can communicate with a central server,
usually over phone lines using a modem.
All of these appliances engage in networked communica-
tion. The simplest handle only one transaction at a time,
requesting information from a server and then waiting
for a response, or sending a single message in response
to some physical event. Others manage multiple streams
of communication at once, allowing you to surf the Web
while watching television. The more processing power a
given device has, the more it can handle. For many applica-
tions, however, you don't need a lot of processing power,
because the device you're making has only one or two
functions.
X
1
2
3
4
Figure 4-1.
New parts for this chapter:
1.
Arduino Ethernet shield—this one has a Power over Ethernet module on board
2.
Photocells
3.
Red, green, and blue lighting filter gels
4.
Voltmeter. You can use an off-the-shelf one, but it's better if you can find
one that's antique. Don't forget plenty of male header pins for the breakout boards.
