Building Wireless Sensor Networks

Chapter 6. Sleeping, Then Changing the World

Whew! At this point, the book has covered a lot of ground and you have come a long way in a very short time. Now we’ll ease the pace just a bit and address some nuances of ZigBee mesh networking, including sleep mode, end devices, and power management. Then it’s time to change things in the world with direct actuation. This chapter features a powerful control project you could use to automate your home or to play Pong using the window lights in a skyscraper.

Sleep Mode

Going wireless often means cutting the electric cord. Projects that are mobile or remotely located frequently use batteries or another constrained power source that demands economizing on energy. XBee radios, like many other communications and microcontroller devices, can put themselves into a temporary sleep state where nearly no current is consumed. The trade-off is that during this state no activities can take place. During sleep, the device is almost completely turned off and is incapable of receiving or sending messages until it wakes back up. ZigBee mesh networking is specifically designed to smoothly handle communications on a network where at any moment many radios might be in this type of low-power state. In fact, by getting very stingy and using the right kind of power cell, we can envision ZigBee networks where batteries last many years at a time, while the networks still perform sufficient sensing and dependable actuation.

End Devices

We introduced end devices