Electronic Design

A ZigBee Mote In God’s Eye

Ok, I stole the title from Larry Niven and Jerry Pournelle but it was just too good to pass up. In this case the “mote” is a small ZigBee node from Crossbow Technology. The motes in the WSN Professional kit I reviewed are just one platform of many from Crossbow Technology. There are mote buttons or dots that are smaller. The work with motes actually grew out of a Defense Advanced Research Projects Agency (DARPA) project at Berkley. Crossbow Technology’s products are practical implementations. The kit consists of six motes, one reference mote board designed to connect to a data acquisition board, and a base station that has inside it, of course, a mote. Each mote has an Atmel ATMega microcontroller with up to 512Kbytes of data flash divided into four blocks or slots. Programs can be loaded into the flash of the microcontroller that varies depending upon the platform. This particular one has 128Kbytes that includes the mote software. It also has an 802.15.4 transceiver capable of handling ZigBee. A number of different versions of the Mote are available. The MDA320 data acquisition board contains the same MICAz Mote board as the other units. The main difference is that this board is mated to the acquisition board. The Mote modules are designed to make a larger network. These modules include the MTS400CB sensor that can detect ambient light, relative humidity, temperature, 2-axis accelerometer, and barometric pressure. All the Motes can be reprogrammed using the USB board although typically a developer will work with the data acquisition board. An Ethernet gateway is available as well. The system works with Windows-based MoteView, Crossbow Technology’s management and development system. It is similar in function to Daintree Networks’ MDA but MoteView is specific to Crossbow Technology’s Motes. Although more restrictive, it is actually more powerful within a network of Motes because it understands the capabilities of the Motes and it can acquire data from the network making it more than just a network sniffer. In fact, MoteView front ends an SQL database. In its most basic form, MoteView allows a developer to work with a wireless mesh network without any programming right out of the box. Just plug in the base station, install MoteView and spread around the six standalone motes. I had the network up and running in under an hour including logging of environmental data. Motes can be used without any programming because of their built-in software. The system can be customized using command line scripts accessing the database and base station as well as configuration parameters that can be sent to the motes. Working With Motes Motes are usable out of the box. They have addition IO that can be wired up to other devices and these interfaces can be accessed without reprogramming the motes. Still, sometimes the motes need more real time control to process or filter IO. For this you need to turn to MoteWorks. MoteWorks exposes the innards of the system that include the XMesh protocol stack that runs atop 802.15.4 and ZigBee. It supports features such as debugging and over-the-air programming. It also provides access to the XServe middleware that sits between clients like MoteView and the motes themselves. The mote system consists of a number of components such as the open-source TinyOS operating system (TinyOS Plus ZigBee Stack Targets Tiny Tasks, ED Online ID #12927). Arch Rock also uses TinyOS in its wireless sensor platform that is similar to MoteWorks. Unlike most 802.15.4 or ZigBee development platforms, MoteWorks insulates developers from the complexity of interfacing with protocol stacks directly. Applications ride atop TinyOS and utilize the other MoteWorks APIs (application programming interface). This allows data to be automatically exposed to MoteView. This provides an infrastructure that developers normally have to build from scratch with other platforms. The ZigBee profiles begin to provide a similar environment though it is not as complete. Related Links Arch Rock Crossbow Technology

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