Look Who’s
Talking!
Explore this
simple method
that lets you and
your robot play
together in a
wireless world!
By Fred Eady
PHOTO 1. This is the MRF24J40MA module variant that is
designed to interface to the PICDEM Z development platform.
Note that the surface-mountable version of the MRF24J40MA
module is actually soldered onto the PICDEM Z 12-pin socket
carrier printed circuit board.
Robots are much like people.
There are soldier robots and there
are hunter-gathering robots. There
are thinking robots and robots that
perform physical work. Robots also
have another commonality with
their human counterparts. They
need to communicate. This
communication can occur in the
form of internal system to system,
robot to robot, human to robot, or
robot to human. This month, we’re
going to explore a very simple
wireless method of invoking
internal-to-internal, machine-to-machine, and machine-to-human
data communications using the bus
that ZigBee rides — 802.15.4.
48 SERVO 04.2010
What is 802.15.4?
Formally known as IEEE 802.15.4, the 802.15.4
standard specifies the rules for the MAC and PHY layers
used for low power networks. The MAC (Media Access
Control) layer is responsible for logically handling the
transmission and reception of data that passes through the
PHY. The PHY layer is comprised of the actual hardware
that moves the data. The hardware can be wire or a radio.
The most popular protocol implementation of the 802.15.4
standard is ZigBee which uses 802.15.4 to fly ZigBee
packets around in a ZigBee network. The low power
networks targeted by 802.15.4 are commonly used for
monitoring and control. ZigBee — which is designed for
monitor and control purposes — is a good example of a
typical 802.15.4-based network. The IEEE 802.15.4
implementation is actually a part of the 802.15.4 wireless
PAN (Personal Area Network) specification. PANs are simple
packet-based networks that usually support sensors and
battery-operated devices.
The interesting aspect of battery-powered devices that
work on PANs is their battery life which is commonly
measured in years instead of hours. The factors that
contribute to a PAN node’s long battery life are the length
of the messages and the distance between nodes. PANs
more often than not are designed to transfer low
