RADIO STANDARDS

Thanks to Tom Cantrell, I don’t have to cover the topic of emerging radio standards in too much detail. In “Radio Riot,” Tom briefly described ZigBee, Bluetooth, UWB, 802.xx, and Z-Wave (Circuit Cellar, 167, June 2004). I’m interested in where ZigBee fits in.

First of all, let me be clear about the comparisons I’ll make. I’ll make some assumptions about what’s important for your projects and then describe the best solution possible.

Sophisticated MAC and a spread spectrum modulation scheme should be built-in. This rules out Z-Wave and any garage door opener type of devices that rely on OOK/ASK/FSK or require you to cook your own protocol for low-level access to the air interface. I want sophistication, but I don’t want to deal directly with the complexity or have my application processor bogged down by low-level transceiver control. Secondly, I assume you want to integrate wireless capability as a small subsystem of a project that uses an 8-bit microcontroller. If you already have a laptop in your design, stop reading right here and plug in an 802.11 PCMCIA card.

Size and power consumption are also important. You should be able to place the transceiver IC and discretes directly into your design without having all the extra garbage associated with evaluation boards getting in the way.

I don’t need 20-Gbps data rate or 20-mile range, but I want a bits in/bits out solution, which means that channel encoding, CRC checking, and link quality indication are handed to me on a plate. I also don’t want too much of that tricky RF layout stuff. In previous attempts at using RF ICs, my PCBs went straight from my desk to the dumpster. Did I mention I want all this to cost less than $15 per unit? I’m a demanding kind of guy.

Well, some of these criteria have been met, but not all at the same time. Frequency-hopping radio modems with an RS-232 interface are available, but they’re still too expensive.

Other solutions place too much emphasis on the process of trying to transfer as much information as possible in the most sophisticated way. What about the less-sophisticated nodes such as light switches and thermometers that don’t need to play video streams or transfer 3-MB MP3 files? What’s more, these types of nodes potentially outnumber cell phone-like devices by an order of magnitude. I have three phone-type devices in my house, but 22 light switches.