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WHAT? If you’d been off the planet for the last five years and considered a snake’s pit of cables linking computers and peripherals as normal, then today’s wireless connectivity could come as quite a surprise. C onsumers hate cables – and many Y2K era PCs had over a dozen of them. Although obviously wire and connector free, wireless linking traditionally involves tradeoffs between power, range and speed. Thus low power modules like the 433MHz units we’ve recently featured have fair range but only slow data speeds, while faster rates (900MHz cellular, etc) come with higher power demands, not easily met by batteries. by Stan Swan Much higher frequencies, such as the license-free 2.4GHz slot, offer greater bandwidth so more data can be squeezed into the same signal spectrum. However microwaves are very line of sight, so ranges may be greatly reduced. Phew – it’s all compromises... Acting in a similar manner to line- of-sight microwaves, infrared data remained the only easy wireless technique five years ago, although its need for clear links meant IR could never punch data pathways through walls, filing cabinets . . . or even paper. To overcome this limitation, WiFi (IEEE802.11x) – which itself has undergone three recent revamps (a,b,g with “n” due this year) – and Bluetooth (IEEE802.15.1) evolved. Bluetooth, although initially a sleeper, now features in almost all new Larger-than-life pics of MaxStream’s XBee (1mW) and XBee Pro (100mW) ZigBee devices. Expect prices to be in the $20-$30 range when they start arriving! 72  Silicon Chip siliconchip.com.au Name WiFi IEEE title Speed Range Power Hardware Cost Typical use IEEE802.11g to 54Mbps 300m Modest PC or AP Modest PC WLAN Bluetooth IEEE802.15.1-2 1-2Mbps 10m Low Camera/ Low cell phone Consumer PAN (to 8 devices) ZigBee IEEE802.15.4 250kbps 30m Very low Microcontroller Very low Low duty cycle (255 devices) Comparison between WiFi, Bluetooth and now ZigBee wireless systems. As you can see, WiFi is still king of the roost when it comes to range but ZigBee offers many advantages over Bluetooth – range included. Consume PAN (Bluetooth use) stands for Personal Area Network. cellular phones and such consumer peripherals as headsets, photo printers and PDAs. The Bluetooth title incidentally honours tenth-century Viking King Harald of Denmark, famed for feasting on blueberries until his teeth apparently were stained blue. His administration skills however were even more legendary, since for a period (no doubt in their blueberry off season) he managed to unify the war-mongering provinces of Scandinavia to work together (maybe raiding neighbouring blueberry patches!), much in the way that today’s Bluetooth seamlessly links cameras, PCs, headsets, and cell phones etc. You may groan with the nearbewildering rate of progress and worry about security and 2.4GHz “RF smog” but now there’s a further offering. ZigBee! In an attempt to simplify wireless data communications, yet another approach has recently emerged and is showing considerable industry support and promise. Formally based on IEEE 802.15.4, it’s better known as ZigBee. No, ZigBee is not just a whacky marketing title dreamt up over a 4-hour liquid lunch. Instead, it honours the energy-efficient zigzag “waggle dance” of honey bees, which directs worker bees to nectar sources. It was first studied by Austrian zoologist Karl von Frish in 1943. Available at 915MHz and 2.4Ghz (with the lower 915MHz being just 20kbps), ZigBee has several power ratings, with just 1mW the most common. It’s somewhat of a Bluetooth “lite” since, although it has similar crossroom range, it’s slower but far more energy efficient. Remember that tradesiliconchip.com.au off above between range, speed and power? ZigBee is further able to be implemented with simpler electronics and (in time) may be so cheap that even light switches could have it inbuilt, leading to more flexible and cheaper control layouts. Yes, wireless light switches! Given the obscene costs now associated with 240VAC fittings, mains cabling, conduit and redecorating (not to mention the difficulty of relocation), this may be a very welcome development indeed. The table above is a brief feature summary of these three main wireless data technologies. All are on the globally license-free (and increasingly “noisy”) 2.4GHz band. Power demands of ZigBee devices are so tiny that low duty-cycle applications may average current drains of only microamps, allowing batteries to last years – approximating their shelf life. Marketing is already playing on this benefit, with “Five years off a few AAs” noted! Solar powering from scavenged room light may even be feasible. A more dramatic feature however relates to the relaying of data to a specified address on the 255-device ZigBee network. This conjures up visions of your door keys relaying “Hi family, I’m home” details to the beer fridge, via perhaps a network of ZigBee devices in light switches and ad-hoc networked sensors throughout the house. Unlike the simplex and error-prone nature of 433MHz units, handshaking for data reliability is supported too. This makes more professional applications attractive, suiting drive-by utility monitoring and on-demand telemetry, etc. Although only ratified late 2004, many makers already offer modules, typified by the postage-stamp-sized “XBee” from US firm MaxStream (www.maxstream.net). These come as either a 1mW or a more powerful and sensitive longrange 100mW “XBee Pro” and allow easy RS-232 or USB connections to suit microcontroller interfacing. Both look very “user friendly”, with Hayes-style “AT” command radio modem features, although the low Picaxe serial data rates (typically just 2.4kbps) may rather “waste” the 250kbps Xbee horsepower. Since high-gain 2.4GHz antennas are compact and very easy to organise (see www.usbwifi.orcon.net.nz), lineof-sight control ranges to a kilometre should be feasible with even the 1mW version All manner of exotic applications arise with this new technique, the least of which could be ZigBee-fitted and powered solar garden lamps, all “chatting” across the neighbourhood and winking mesmerising messages together while exchanging wireless data about their owners’ lifestyles. They’ll probably be all the rage by next Christmas… SC References: Get used to the ZigBee logo . . . you’re going to see a lot more of it shortly! References are conveniently hosted at www.picaxe.orcon.net.nz/zigbee.htm February 2006  73