Letters

I read your article about tire pressure monitoring ("Testing the MEMS revolution," April 2004) with great interest. In the early '90s, I was part of a tire-pressure monitoring project with a company called Tyre Trac. The company went under for lack of funding.

The product we worked on was an after-market device targeted at large, over-the-road trucks. We mounted the transmitter on the axle end to minimize tire balance changes. The pressure sensor was a switch assembly that replaced the valve stem cap.

The switch was set to trip at the lowest pressure that the truck should have. The transmitter used an ASIC that Motorola designed for us that sent a data stream to the dash-mounted receiver about every 5 minutes.

The transmitter batteries were expected to last about 10 years. The transmitter required about the same average current as lithium battery shelf life.

We designed an interface to our product that would report to the truck-line dispatcher through the Qual Com satellite communication system any low-tire, hot-brake, or over-temperature condition (refrigerated trailer) that our transmitter/sensor system detected.

Our first on-truck test failed and we could not figure out why. After manually testing the tire pressure, we found that every tire on the truck was under inflated. A lot of drivers like to run their tires a bit soft for a better ride.

As far as I know, Motorola never did get paid for the ASICs that they built for us. Maybe the MEMS product will compensate for that, only 12 years late.

RICHARD W. WILSON, RETIRED ENGINEER, BLUE SPRINGS, MO

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