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DAZED AND CONFUSED

by Tom Cantrell

Start ı BalkLANization ı Pain in the Pan ı Whatıs All the Buzz About? ı Rock Around the Clock ı Sources and PDF

PAIN IN THE PAN

In "BluetruthıHouston, We Have a Problemı" (Circuit Cellar 134) I took a few pointed jabs at the hype balloon surrounding Bluetooth. While recognizing the marketing momentum coupled with a generic need for a low-end (i.e., sub-802.11) RF standard, I lamented the cost and complexity, not to mention the wishful thinking forecasts from Bluetooth zealots. Iım not dissing the clever folks behind the scheme. Itıs more a matter of their particular perspective and perhaps biting off a bit more than silicon and application providers can chew.

I can see Bluetooth slowly but surely making its way into cell phones, PDAs, notebook PCs, and other gadgets in the modern road warriorıs arsenal. True believers would have the Bluetooth radio in their shoes ring their cell phone to tell them their shoe is untied. But, what about simple blue-collar household and industrial applications such as meter reading, security, HVAC, sensors, actuators, and such? Consider something as simple as the thermostat controlling your furnace.

The last house I lived in had the thermostat mounted near the front entryway. That meant that leaving the door open for more than a few seconds, especially on a cool windy day, would invariably trigger a generally unneeded and inevitably short-lived and wasteful heat cycle.

Iıd often contemplated moving it somewhere practical, but I never got over the hump of stringing wire through the attic and poking holes in the wall. Just what the world needs, a wireless peel-and-stick thermostat with no installation skill or effort required beyond deciding where you want it and easily moving it when you change your mind.

For an application such as this, Bluetooth is both under- and over-kill. At about 1 Mbps, Bluetooth comes with laughably more bandwidth than required. Furthermore, most of the protocol complexity needed to deal with Bluetoothıs presumption of mobility and ad-hoc connectivity is unnecessary. The thermostat has no need to be continually on the lookout for new devices, service discovery, and all the rest. And needless to say, battery life needs to be measured in months or years, not weeks or days.

Yes, long-term, full-production volumes will push Bluetooth costs down. But, even the still mythical $5 target touted by advocates is too much baggage for a $20 to $30 retail item to carry. As it stands today, a typical Bluetooth implementation demands a 32-bit CPU and a bunch of memory for baseband processing, in addition to the radio itself. Iım all for the march of silicon, but I must say the idea of needing so much horsepower just to get a few bits from here to there does offend my engineering sensibilities.

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