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Designing Z-Wave devices

Posted: 02 Nov 2012 ?? ?Print Version ?Bookmark and Share

Keywords:communication protocol? antenna filter? frequency bands?

Z-Wave has become the rising star of smart home technology with now more than 700 interoperable devices in the market. It opens a great opportunity for newcomers to add smart and new ideas to this large ecosystem of interoperable products and leverages the existing installed base.

This article describes the development process and the tools available to design and test Z-Wave compatible devices. Technically, Z-Wave is a specification for a low bitrate communication protocol that allows different devices in buildings to communicate with each other wirelessly. These devices include fix-installed gear such as light switches and heating control, mobile devices such as remote controls and also gateways to internet based services on mobile phones or in the Internet. The specification covers all aspects of the communication from the radio layer up to the way devices generate events and execute actions. Only devices with complete implementations of all aspects of the communication protocol are called Z-Wave compatible or short a Z-Wave certified device.

Hardware
To support the Z-Wave radio layer a special Z-Wave transceiver hardware is needed. The main supplier for this transceiver is the US company Sigma Designs. A second supplier, Mitsumi Corp., offers a function and pin compatible silicon. The current chip generation of Sigma Designs is called Series 400 with the ZM4101 as standard component. Sigma or Mitsumi do not sell separate radio transceivers but the radio as one part of a whole SOC. The radio transceiver is available as a chip to very high volume applications where it can be embedded in the base designs but most customers purchase a SOC that integrates all functions of a computing system with radio interface:

???CPU Core, compatible to 8051
???Radio transceiver with receiver and transmitter
???2 KB-16 KB Internal SRAM
???32 KB-64 KB ROM
???Several Peripherals
The series 400 comes equipped with one-time programmable memory making it ideal for cost sensitive designs where reprogramming isn't required. The vast majority of applications use the Series 300 chip and its Flash based memory. The re-programmable Flash memory is better suited to development programs and applications that require updates from time to time.

Sigma Designs has announced the next generation chip called Series 500 to be available in 2013. This chip series will be pin and function interchangeable with the Series 400 but will replace the Series 400 OTP with Flash memory.

The most commonly used module ZW3102 from Sigma Designs combines the Series 300 chip with some capacities, a crystal and most importantan antenna filter.

The antenna filter is needed to comply with the regulations of the license free frequency bands used for Z-Wave. These antenna filters are frequency-specific for e.g. 868.4MHz (Europe, Africa and parts of Asia) or 908.4MHz (North America) and turn the modules into a region specific device. As a result different hardware exists for different frequency bands and manufacturers have to manufacture separate hardware e.g. for the European or the US market. The modules can be ordered either directly from the manufacturers or from Digikey (http://www.digikey.com), the worldwide distributor of Sigma Designs. The price point depends on volumes but a budgetary estimate of US$ 5-6 can be assumed for small production volumes of few thousand modules.

The module fans out all I/Os of the SOC. These I/Os are multipurpose I/Os and can be freely programmed as output, input with or without internal pull up. Certain I/Os have special functions to support commonly used circuits such as dimmers or motor control.

I/Os for the Series 300 are:

???10 * General Purpose
???Two Interrupt Inputs
???Serial UART
???SPI Interface
???Triac Control, allows directly attaching the Zero Crossing signal of a phase edge dimmer circuit and deliver the Triac control signal to design a dimmer with minimum external components.
???PWM Output
???Four multiplexed 12/8 bit ADC inputs
Generally the flexible I/O concept and the module approach allow designing products with minimal additional cost. Assuming a project for a simple binary sensor powered by a battery the whole product can be designed with as few as 10 additional components including the external antenna.

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