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Chips monitor tyre pressure US electronics giant Motorola is set to introduce computers into the last electronics-free zone in a car – its tyres. The company has developed a two-chip remote sensing module (RSM) small enough and light enough to fit inside a tyre without unbalancing the wheel. A sensor chip, code-named Daytona, measures pressure to within 7.5kPa (typical car tyre pressure is 220kPa), and temperature to within 4° Celsius. Temperature measurement is necessary to compensate for pressure changes due to tyre heating during driving. The Daytona chip is fabricated using low power CMOS technology and draws just 0.55µA on standby. The second chip in the RSM is a combination of Motorola’s HC08 microcon-troller and a UHF radio transmitter in a 32-pin package. It processes the raw measurements into a tyre pressure reading and transmits the data to the in-car receiver. 82  Silicon Chip The transmitter operates in the 315, 434 or 868MHz bands, sending the pressure data at up to 9600 baud by either on/off or phase shift keying. The HC08 has 2Kb of on-board FLASH memory and enough I/O and computing power to handle the pressure and temperature reading task. It also has built-in power management capabilities to get the most out of the lithium battery powering the module. When the car is parked, an inertial switch can be used to turn off the transmitter and leave the HC08 in low power sleep mode. By PETER HOLTHAM These power-saving features of the RSM will ensure a battery life of at least ten years. A simple PC board antenna completes the RSM hardware. It provides a signal strong enough to be picked up by the receiver inside the car. Making the module is one thing, keeping it alive in the harsh environment inside a tyre is another. Temperatures can range from a freezing -40°C to a scorching 150°C . The RSM is also subjected to accelerations as high as 2000G as the wheels rotate. The computer and transmitter can be protected but the pressure sensor must be in contact with the air in the tyre. Motorola engineers have develwww.siliconchip.com.au oped a special Teflon filter to protect it against attack by liquids, dust, and corrosive gases. The tyre pressure signal is picked up inside the car with the same receiver already installed for remote keyless entry. The information presented to the driver will depend on the software programmed into the HC08 and the receiver by car component suppliers. It could be as simple as a dashboard warning light showing that one of the five tyres (including the spare) needs pumping up. More complex systems will automatically identify each tyre and provide the exact pressure. Motorola plans to begin volume production of RSMs in September this year. The price will depend on end-user requirements and will vary based on volumes and specifications. But with around 50 million cars produced every year, demand for remote tyre pressure monitoring is expected to soar, driving prices down. All of which means monitors are likely to become standard equipment within the next few years. KALEX PCB Makers! • High Speed PCB Drills • 3M Scotchmark Laser Labels • PCB Material – Negative or Positive Acting • Light Boxes – Single or Double Sided; Large or Small • Etching Tanks – Bubble • Electronic Components and Equipment for TAFEs, Colleges and Schools • Prompt Delivery We now stock Hawera Carbide Tool Bits Other Manufacturers Join The Fray Given the huge global market for new cars, Motorola was not going to be left as the sole supplier of tyre pressure monitors for long. Now European electronics company Philips has launched a rival chip to assist in the measurement of individual tyre pressures. The P2SC signal-conditioner works together with pressure sensors built into the tyre. It mounts directly on the tyre rim, providing a wireless link to transmit the pressure to the keyless entry receiver in the car. The monitor inside the car sends a low frequency ‘wake-up’ signal to www.siliconchip.com.au each P2SC chip every time the ignition is switched on. The chip returns pressure information at frequencies in the 315 and 434MHz bands. While the car is being driven, the P2SC chips send regular status reports on each tyre back to the driver. The low frequency wake-up also allows the monitor to automatically identify which tyre is where; even after tyre position is changed during maintenance. Industry analysts expect pressure monitors to become the fastest growing segment of car electronics over SC the next few years. 718 High Street Rd, Glen Waverley 3150 Ph (03) 9802 0788 FAX (03) 9802 0700 ALL MAJOR CREDIT CARDS ACCEPTED January 2003  83