Tips for Designing ZigBee Applications

So that you suppose you need to develop a ZigBee software, however you have got some questions. What’s essential in a ZigBee growth? What instruments do I want? What steps are concerned? How a lot time will it take? What sort of funding is required? What are the unexpected questions?

The information offered right here cannot reply all of those questions for everyone, however they’ll present a tutorial for the event of your ZigBee software.

The primary and maybe most essential step in growing your software is to find out whether or not ZigBee is acceptable in your product. The ZigBee radio normal boasts many benefits over different wi-fi choices. With a public ZigBee profile and conformant platform, interoperability with different vendor units is assured. ZigBee was outlined to help extraordinarily low energy and remarkably lengthy battery life. However the ZigBee information charges are low relative to different wi-fi choices. And whereas considerably smaller than Bluetooth or 802.11/WiFi, the ZigBee stack is just not a easy piece of software program.

After deciding that you simply need to develop a ZigBee software, you should select a ZigBee supplier companion. A ZigBee companion will provide the ZigBee stack software program together with a radio chip and baseband microcontroller. Traditionally, these have been two chip options. Not too long ago, although, distributors have been introducing single chip ZigBee units with loads of extra sources to help your software code. A top quality ZigBee companion can even provide you with continuous updates on the latest options.

A number of ZigBee suppliers can be found, and every has invested many person-years of growth to reach at their ZigBee answer. In selecting a companion, you need to take into account technical features (the fee vs. functionality of their chipset, supported options) and enterprise features of the supplier (firm historical past, licensing prices, technical help). The ZigBee suppliers can even need to find out about you – info similar to your earlier product growth expertise and the variety of units that you simply plan to promote. When this trade of data is full, you need to quite rapidly be capable of discover a ZigBee supplier prepared to collaborate in your software.

After you have got chosen a ZigBee supplier, you should then resolve learn how to implement the ZigBee radio – as a module linked to the remainder of the system or as a chip built-in into the circuitry of your board.

Utilizing a ZigBee radio module gives many benefits. A module normally results in a shorter growth cycle. The RF design is already executed for you – so that you needn’t grow to be an RF knowledgeable. As well as, a module might carry FCC Modular Approval, which implies you will not need to take your product by way of the FCC’s intentional radiator approval course of.

Disadvantages to utilizing a ZigBee radio module versus an built-in ZigBee chip embody the next per-unit product price. A module design additionally requires extra bodily area contained in the housing and imposes extra constraints on the commercial design of the product. What’s extra, a module might have restricted antenna choices, which can be unsuitable in your product.

The ultimate structure job is to fully outline your ZigBee community construction. The ZigBee normal helps a number of topologies so that you can select from. These embody mesh, star, and cluster tree community configurations, that are proven in Determine 1.

The everyday ZigBee community configuration is comprised of low energy diminished perform finish level units, usually known as sensors. The sensors talk with full perform community management units that deal with the routing of packets over the community.

ZigBee radios might be applied in a number of RF bands. These working within the 2.4 – 2.48 GHz band are the commonest since that is the one RF band that’s usable worldwide. In North America, 915 MHz is offered for ZigBee radios and gives a couple of benefits over 2.4 GHz, similar to barely higher vary. Fewer chip suppliers can be found who provide the decrease frequency vary, as a result of antennas are usually bigger and the over-the-air information fee is decrease. The 868 MHz model of ZigBee additionally gives priceless options, although it’s out there to be used solely in Europe.

Now that every one the structure choices have been made, it’s time to open the event system supplied by your ZigBee companion and dig in. An instance is proven in Determine 2. The event system may have pattern software code to reference. Your closing software will doubtless resemble this pattern as a result of you’ll apply the identical Utility Programming Interface (API) that the pattern makes use of. You may additionally use the identical working system, system calls, and interrupts. Typical API instructions are “FormNetwork()”, “JoinNetwork()”, “SendMessage()”, and “ZigBeeStackTick().” Be taught to like this API – you’ll dwell with it for the subsequent couple of months.

In the course of the growth part, you’ll face many design challenges. Many will contain typical embedded growth points, whereas others will come up since you’ve added a brand new design aspect – the ZigBee stack.

ZigBee advertises extremely low energy. That is nice for the radio – however you must increase that to incorporate your total system design. To completely optimize energy utilization and battery life, the firmware, electrical, and RF groups should dedicate a great deal of time to optimizing energy consumption. As a part of this effort, microcontroller sleep modes have to be outlined and applied. Bear in mind that your growth system might not work correctly whereas the system is in sleep mode. Chances are you’ll want to make use of the old style “GPIO toggle and scope tracing” debug methods.

In case your system can be battery-powered, understand that ZigBee radios don’t violate the legal guidelines of physics. ZigBee radios use the present required to transmit on the chosen energy degree – usually within the vary of 20-50 mA. Reaching multi-year battery life is extremely depending on the utilization situation. Pay explicit consideration to how regularly the radio must get up, how lengthy it takes to get up, and the way a lot present it consumes whereas asleep. Chances are you’ll discover {that a} ZigBee supplier’s information sheets are solely useful to a restricted extent on this space, and you’ll find yourself making your personal measurements on present consumption.

Typically, the principal tradeoff you have to make is information latency versus battery life. It appears counterintuitive; nevertheless, since ZigBee transmissions are at low RF energy – within the vary of a milliwatt – battery energy utilization throughout transmit and obtain modes are comparable. Do not assume {that a} radio mode will use little energy if it spends more often than not in obtain mode.

The ZigBee growth system you begin with will in all probability not match your closing {hardware}. This implies you can be designing new interfaces to your units – buttons, shows, reminiscence, and many others. You may additionally want so as to add a communication channel to a different system, similar to a system monitor PC program. That is the place taking the time to totally perceive the API and your growth system’s place to begin helps, as a result of you will want to merge these new interfaces with the remainder of the present design.

In an effort to confirm interoperability of your system, you might must swallow your pleasure and buy a competitor’s product. Use of one other ZigBee authorized system throughout growth might make it easier to uncover how your product’s efficiency can finest be optimized. Another choice to check interoperability is to take part in one of many ZigBee Alliance’s quarterly interoperability occasions known as ZigFests. To take part in a ZigFest your organization have to be not less than an Adopter class member of the ZigBee Alliance. There are additionally certification firms that may present a pre-certification testing atmosphere.

Keep in mind that, luckily, the ZigBee radio is just not a frequency hopper like Bluetooth. Earlier than the community kinds, the community coordinator scans the out there channels to seek out the “clearest” one. A perform to carry out this computerized frequency choice is normally included with the ZigBee stack you buy, however is simple to implement if not. The community coordinator can then be programmed to periodically take a look at the community to find out if the chosen frequency stays the most suitable choice. If not, the community coordinator can transfer the community to a unique channel with out operator intervention. This insures the community will carry out optimally always.

If information safety is required in your software, ZigBee consists of provisions for sturdy information encryption. ZigBee information safety is predicated on the 128-bit AES algorithm. In case you are utilizing a public ZigBee profile then the safety choices have already been made and are pre-defined within the profile.

For a customized software that requires information safety, you have got choices relating to the place the safety is utilized – within the software code or within the decrease layers of the ZigBee stack. In case your software wants the strongest safety attainable, safe it in your software code. The ZigBee stack defines non-obligatory safety within the decrease layers of the stack, which can be utilized to validate every information packet that’s exchanged in your ZigBee community.

Your growth will almost definitely embody the event of two ends of a system – the sensors, which can be diminished performance ZigBee finish units, and the units with which they need to talk. Every finish of the system will current its personal design challenges. Energy optimization is mostly the biggest design difficulty for the sensors, whereas message administration is the biggest for the ZigBee routers.

Message administration is a vital a part of the applying code. Your software code will talk with the ZigBee stack by sending messages to the stack by calling stack capabilities and receiving messages from the stack by way of callback capabilities. The applying code will doubtless want to observe these messages and should must carry out duties, similar to timing messages and purging “misplaced” messages, on high of its regular community administration job.

As a part of the applying growth planning course of, make sure you embody time to put in writing take a look at code. Throughout your integration part, take a look at code will assist establish and confirm boundary situations of the function operations. Specialised take a look at code could also be required to place the system in perpetual transmit mode throughout {hardware} compliance testing. On the manufacturing facility, correctly designed take a look at code can rapidly and totally confirm operation of every system because it comes down the road.

One software important to designing a ZigBee software is the ZigBee RF sniffer/protocol analyzer. Even when your design makes use of a ZigBee radio module and a public ZigBee profile, you’ll finally want to look at instructions as they’re despatched over the air. Many protocol sniffers are at the moment out there with a variety of capabilities and value. Selecting the sniffer will rely in your expertise with protocol analyzers, the depth of protocol analyzing required, future anticipated ZigBee work, and the price of every unit. Probably the most logical path is to start out with a fundamental unit and improve later in case you want extra capabilities.

Time-to-Market

If time-to-market is a significant requirement for the system, use of a ZigBee radio module is sort of a given. A module-based design will present the quickest growth cycle.

Many tasks require quick time-to-market with a small variety of units to introduce a know-how or a product line. Typically, larger quantity manufacturing comes at a later date. If that’s the case, it might be attainable for a two-phase growth – the “quick” part utilizing a ZigBee radio module and a “cost-reduced” built-in design part to comply with. This price discount part typically entails merging performance from modules right into a single circuit board. The timing of a two-phase method additionally is sensible, as a result of experience is constructed with the know-how earlier than merging the radio chip on the circuit board. Plan forward, and the optimum market rollout is achievable.

Like some other digital system that is dropped at market, your ZigBee software should meet regulatory requirements. Since a ZigBee system is an intentional radiator, the system should meet world requirements. Because the proprietor of the design, you can be accountable for submitting the product for compliance testing, adjusting the design as wanted to go, and submitting the ultimate design with the suitable company. Plan for a number of rounds of testing as early as attainable within the design part. This features a pre-screening take a look at on the radiated emissions.

Since most ZigBee designs transmit on the low RF energy of about one milliwatt, the basic RF emissions aren’t more likely to be problematic. Nonetheless, necessities on emission ranges – notably the second and third harmonics that fall into FCC “restricted bands” – must be fastidiously monitored. You should additionally display much less technical compliance areas, similar to product labeling necessities and antenna limitations.

To promote your product as being ZigBee compliant, your design should undergo ZigBee licensed product testing. To submit the product for ZigBee testing, your organization have to be a member of the ZigBee Alliance. Becoming a member of the ZigBee Alliance is a cheap proposition and must be executed instantly as a result of membership will enable entry to many ZigBee-related paperwork and discussions. Go to their web site at http://www.zigbee.org for extra info.

For each ZigBee product, you will want to generate a novel 802.15.4 MAC deal with. The 802.15.4 MAC deal with is an eight-byte (64 bit) worth. The primary three bytes (the Organizationally Distinctive Identifier or “OUI”) are licensed to your organization by the IEEE Requirements Affiliation for an annual price. Your organization is then free to uniquely assign the remaining 5 bytes.

Lastly, relying on the manufacturing facility meeting and testing course of, it might be fascinating to have a software-based manufacturing take a look at present the MAC deal with to program into every system. On this case, your software code might must help a non-violate reminiscence write perform that won’t in any other case be mandatory.

Conclusion

ZigBee is a well-defined and feature-rich radio normal; nevertheless, growing a ZigBee product is just not a trivial train. Many engineering disciplines should work collectively to outline, architect, design, take a look at and prepared the ultimate product on the market. Following the options set forth on this dialogue will allow you to organize a sensible plan in the direction of creation of a ZigBee radio software.

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