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Tire Pressure Monitoring
The system consists of two print circuit boards, a
transmitter board and a receiver board. A transmitter is placed in each
tire. It is a self-contained battery operated system. There is a
pressure sensor and a temperature sensor on the board. The microcontroller has a data acquisition subsystem
including analog input multiplexer with sample and hold. If the
pressure or temperature exceeds a specified limit the transmitter is activated
sending the information to the receiver.
The vast majority of the time the transmitter
board is asleep in a very low-power mode. The calculated
battery life exceeded three years. The transmission code was critical due to the
rotation of the tire at high speed. A 13 bit burst message fragment was used.
Each fragment included synchronization bits, fragment pointer, 8 bits of data and parity. Several burst
transmissions of a message fragments were required to transmit the entire
message. Each transmitter board had a unique code to differentiate it from
other tires.
 The message
fragments were received and assembled into a complete messages by the receiver
board in the cab, mounted on the dashboard. The message also included horizontal and vertical cyclic redundancy
check bytes.
A liquid crystal display and audio buzzer alerted the driver to
the condition.
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