Hardware Reference
In-Depth Information
Buying Radios
You've seen a few different kinds of wireless modules in this chapter. Though they
do the job well, they're not the only options on the market. You should definitely shop
around for modules that suit your needs. Here are a few things to consider when
choosing your radios.
The wisest thing you can do when buying your radios
is to buy them as a set. Matching a transmitter from
one company to a receiver from another is asking for
headaches. They may say that they operate in the same
frequency range, but there's no guarantee. Likewise,
trying to hack an analog radio—such as that from a baby
monitor or a walkie-talkie—may seem like a cheap and
easy solution, but in the end, it'll cost you time and eat
your soul. When looking for radios, look for something that
can take the serial output of your microcontroller. Most
microcontrollers send serial data at TTL levels, with 0V for
logic 0 and 3.3V or 5V for logic 1. Converting the output to
RS-232 levels is also fairly simple, so radios that can take
those signals are good for your purposes.
mance devices like samplers and lighting dimmers. You
might think that you need your radios to work at MIDI data
rates to do this, but you don't. You can send the sensor
data from the performers wirelessly at a low data rate to a
stationary microcontroller, then have the microcontroller
send the data via MIDI at a higher data rate.
Consider the protocols of the devices that you already
have at your disposal. For example, if you're building an
object to speak to a mobile phone or a laptop computer,
and there's only one object involved, consider Bluetooth.
Most laptops and many mobile phones already have
Bluetooth radios onboard, so you'll need only one radio
to do the job. It may take some work to make your object
compatible with the commands specific to your existing
devices, but if you can concentrate on that instead of on
getting the RF transmission consistent, you'll save a lot of
time.
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Consider the data rate you need for your application—more
specifically, for the wireless part of it. You may not need
high-speed wireless. One common use for wireless com-
munication in the performance world is to get data off
the bodies of performers, in order to control MIDI perfor-
What About WiFi?
So far, you've seen the most basic serial radios in action in the transmitter-receiver
project, and more advanced radios at work in the transceiver projects. If you're thinking
about networks of microcontrollers, you're probably wondering whether you can
connect your projects to the Internet and to each other using WiFi. You can, but there
are complications to consider.
Until recently, WiFi wasn't very common in microcon-
troller projects for a couple reasons: cost and power.
Microcontroller-to-WiFi modules on the market are more
expensive than equivalent transceivers implementing
other protocols. That's starting to change. Many earlier
WiFi modules were also power hungry, but that too is
changing.
There are currently a few WiFi solutions on the market.
Spark Fun makes the WiFly shield, and Digi just announced
WiFi versions of their XBee modules. There's also a forth-
coming Arduino WiFi shield, which is designed to be easy
to incorporate into an existing Ethernet project with only
minor code changes. A short introduction follows.
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