What are a few fingers worth?

As a journalist, I'm not easily impressed, but some applications and demos are simply irresistible. A low-power demo and a new unique application using a Texas Instruments microcontroller to reduce serious table-saw injuries caught my eye—and not my fingers.

I am one those idiots who immediately removed the blade's safety guard when I bought my 10-in. contractor's saw a few years ago. It's like the bike-helmet thing: Convenience, hubris, and a no small amount of stupidity superseded safety considerations, even though my fingers on numerous occasions came perilously close to the blade as I shoved stock across the table. Don't try this at home.

Now, a marvelous-sounding technology, SawStop, could protect me against myself. It senses when fingers or flesh come into contact with the rotating blade and instantly shuts down the saw. The company, SawStop LLC, uses a hot dog in its demonstrations, and the video is dramatic (Link 1). How does it tell the difference between wood and flesh?

A TI LF2403A microcontroller detects changes in the constant 3V charge in the blade during normal use. The capacitance of the human flesh causes a voltage change that the device can sense in about 50 µsec. Once the 40-MIPS controller detects that fingers or skin are at risk, it trips a single-use actuator that promises to retract and stop the blade in less than 5 msec. The result is a nick instead of a severe wound or dismemberment.

Fearing price disruption in a highly competitive market, none of the major saw makers has signed up for the technology. SawStop's principal inventor, Steve Gass, planned to license the technology, which he says adds about $150 to the price of a saw, to those manufacturers. Meanwhile, the company is making its own saws and encouraging consumers to contact other saw makers to insist that they adopt his technology.

"It's not just humanitarian. It's economically justified," argues Gass, who claims the economic and direct costs from table-saw injuries amount to $2 billion annually. "The [average] cost per injury is about 10 times the cost of a saw. Think about what an injury costs a school district."

Gass has petitioned the Consumer Products Safety Commission, the folks who bring us product recalls, to create safety standards that could made his technology mandatory. The petition, which includes a letter from a physician who lost three fingers to a table saw, has stalled, and Gass is not optimistic it's going anywhere in the face of lobbying from manufacturers.

We've been down this road before. "Think a few years back about air bags. Everyone wondered if they would inflate," says TI Microcontroller Marketing Manager Mark Buccini. "If the cost can be driven down, it could make sense." Indeed, it's a compelling application fighting its way toward acceptance.

The point Buccini was trying to make with the low-power demo was to show how little juice an LCD and microcontroller require. Using Apple slices, a zinc-plated washer, and a penny to form a battery, he generated 1.5V and 1.5 µA to power the display.

"Any acidic fruit works. You can use an orange. People have done it with grapes and potatoes," he says, explaining that each combination of apple slice, penny, and washer generated a 0.5V. Who says engineering can't have a little theater?

Tell me about your unique or offbeat applications. Write me at john.dodge@reedbusiness.com.

1. www.sawstop.com/video.htm