Making Things Talk

SESSIONLESS NETWORKS 251

Figure 7-16

ITP students Angela Pablo

and Gilad Lotan with the

solar battery pack and

XBee monitor radio.

Figure 7-17

Network diagram for the

solar project.

Sensor XBee

Radio

Internet

RelayXBee

Radio

XPort XBee

Radio

XPort

Processing

program on

personal

computer

The XBee radios can be configured as a mesh network,

using the ZigBee protocol. In a mesh network, some radios

function as routers, similar to how the relay radio works

in this project. Routers can not only relay messages,

but can also store and forward them when the radios

at the end node are not on. This provides the whole

network with net power saving, as the end nodes can be

turned off most of the time. At the time of this writing,

MaxStream’s implementation of the ZigBee protocol

was not fully finished, so this simpler solution was used.

MaxStream recently announced a second generation

of the XBee radios, which uses a different chipset and

implements the ZigBee protocol better than the original

did. For more information, see www.maxstream.net.

Mesh Networking

from the solar cell like batteries, to keep the radio’s supply

constant. Figure 7-18 shows the circuit.

The XPort radio circuit is identical to the one used in the

last project. Build it as shown in Figure 7-9.

Making_Things_Talk.indb 251 11/13/09 4:55 PM

252 MAKING THINGS TALK

MATERIALS

» 1 USB-to-TTL serial adaptor You’ll use this for

testing only ...