Electronic Design

ZigBee Bonanza

Technology Editor Bill Wong begins a series of reviews on new ZigBee kits

A lot has changed since I first tried out ZigBee kits. Though I’ve been delinquent in reviewing new kits, that’s about to change. This is the first in a series of articles that sorts out the stack of kits that has piled up over the past year. This series will group a handful of kits with each main article. If you don’t see the one you want, let me know; I may have it in the queue. 802.15.4/ZigBee Mayhem and Modules The buzz around 802.15.4 and ZigBee has been steadily increasing as things have moved from paper standards to chips and modules. For those new to the technology, 802.15.4 is one of many low speed (250Kbits/s), short range (100m) wireless technologies (See "Short-Range Wireless Needs Long-Range Plans"). It is the basis for ZigBee and it can be used without resorting to the ZigBee stack (See "ZigBee Or 802.15.4 Network Layer—Is There Room For Both?"). In fact, there are a number of stacks built on 802.15.4, but that’s for another article. Still, ZigBee is adds a number of features not found in the basic 802.15.4 protocol stack. The ZigBee standard defines additional layers and services such as self-healing mesh networks. 802.15.4 provides the basic plumbing but ZigBee makes the house livable. In fact, home applications will be a major target of ZigBee products. The ZigBee standard is managed by the ZigBee Alliance. The standard definition includes the idea of profiles that provide a layer of interoperability between products. Profiles are being defined for a range of applications such as HVAC (heating, ventilating, and air conditioning) and Home Automation. In theory, products that support a particular profile should work with each other. For example, a Home Automation ZigBee switch should be able to turn a Home Automation ZigBee light on and off. The ZigBee standard and ZigBee Alliance bring a good bit to the table but initially there was some confusion regarding who needs to join the Alliance (See "ZigBee Surprise"). Not surprisingly, The Alliance now posts its membership and certification links on its main site and some vendors are starting to include similar information in their development kits. Why is this necessary? Because working with wireless is not just a matter of ordering a chip, plugging it in, adding a protocol stack and selling the product. If you want the ZigBee logo on your product then it is time to dig deeper. This is true whether you use raw chips or modules. The kits and software in this set of reviews and subsequent articles in this series address the chip, module and software aspects. In general, software stacks will be a “buy, not build” issue and there is quite a bit of variance between each vendor in terms of features, performance and licensing. For hardware, if you start with a chip then be prepared for some major discussions with the FCC. Everything built from scratch must be approved, and the process is not cheap for small runs; amortizing the costs over tens of thousands of products can have a major impact. This is where modules often come into play. Modules typically package a wireless chip and possibly more, for instance a microcontroller that often has the protocol stack built in. The interface to the modules is often via a serial interface such as SPI (serial peripheral interface) or I2C (Inter-Integrated Circuit). The modules are FCC-approved but their use is not so it is a quick way to incorporate wireless technology into a design. Tools and Kits In Review To start this series, I take a look at a diagnostic tool and two module-based solutions. I am doing these reviews pretty much on a FIFO basis so don’t look for a major trend in my choices. The diagnostic tool is Daintree Networks’ Sensor Network Analyzer (SNA). It is often bundled with other vendors’ hardware and development kits. If not, there is usually a comparable application, although not always as capable. Working without an analyzer is just nuts since a developer is essentially blind to what is actually happening on a network. Rabbit Semiconductor’s offering utilizes MaxStream’s XBee OEM RF Modules. It combines this with the RCM3720 module based on the Rabbit 3000 microcontroller. The XBee modules can be combined with most of Rabbit Semiconductor’s Rabbit 3000 and Rabbit 4000 modules. The RF modules utilize an AT-style serial command set, and can operate in a standalone mode or combined with a microcontroller. Crossbow Technology’s solution is also module-based. Its Mote technology provides a robust mesh networking environment. The reviews in this series are targeted at kits designed to provide out-of-the-box support for developers versus demo kits or platforms designed for protocol stack development. While it is possible to get something up-and-running in a day with these kits, the time-to-market can vary significantly depending upon the level of customization in the final product. This is especially true if you plan on building a design into your own board. That requires FCC approval, which is a whole other story. Chips tend to be under $5 while modules start at $20 and go up depending upon their functionality. All will operate off batteries but the battery lifetime is variable since it can be affected by how long a node may be active. Be careful when reading specs and designing systems. Your mileage will definitely vary. Most of the kits in this series are at least second- or third-generation so they are significantly more polished than kits addressed in prior reviews. We will be looking at 2.4GHz and 900MHz versions. Check out the first review: Sniffing ZigBee Related Links ZigBee Alliance

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