THE DESIGN CYCLE
■ BY FRED EADY
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
HERDING DATA OVER BRIDGES
Small autonomous
networks are wonderful
things. Data flies about
from node to node. Relays,
LEDs, and switches submit
to the modulated RF
energy. Things are good.
Well, things are good until
you want to intrude on the
data exchanges and
harvest the bits and bytes
for human consumption.
Small self-contained
networks are like cattle.
You can fence them in and
they get along just fine.
When you need access to
them, you open the gate
and enter their domain.
Our silicon cattle normally
stroll around in the
Industrial, Scientific, and
Medical (ISM) grass and
feed on the 802.15.4
protocol. To keep tabs on
the data within the herd,
we as humans must have
similar beasts that can
speak to the silicon cattle
and to us. That interpreter
is known as a bridge. Once
we "cross the bridge" with
our data, we can distribute
it using a gateway.
This month’s discussion will center on moving data back and forth
between a small embedded network
and the Internet. It sounds like a
daunting task. I’ll show you how to
make it look easy.
CROSSING THE
FIRST BRIDGE
The radios in our small network
can pass data between each other till
the cows come home. What good is
that data if we can’t access and use
it? Odds are the radios are controlled
by something. That something is
usually some type of microcontroller.
The microcontroller is the first bridge
that the data flying within our tiny
network crosses.
For example, the radio you see in
Photo 1 is a Lemos LMX-ISM-242-LR.
The LMX-ISM-242-LR is a high power
version of the LMX-ISM-242-SR we
discussed in last month’s Design
Cycle. The LMX-ISM-242-LR contacts
other LMX-ISM-242-LRs and LMX-
ISM-242-SRs in the network using
GFSK-modulated packets.
A DROP-IN GATEWAY
PANs (Personal Area Networks)
■ PHOTO 1. The LMX-ISM-242-LR's maximum power output is 100 mW.
We can put this radio to work using the same driver package
that we constructed for the LMX-SR.
14
February 2013
