Abstract: In detecting which transmitter of several of transmitters has transmitted a radio signal based on digital data from an RF circuit, a main controller of a receiver consecutively sends activation commands to each of several control circuits such that only one of the control circuits is activated at a time. The main controller detects which of the antennas corresponds to the control circuit that was activated when the voltage level signal from the RF circuit was lowest, and judges that the detected antenna is closest to the transmitter that transmitted the radio wave. As a result, the power consumption is reduced, and the transmitter that transmitted the radio wave is accurately detected.

Abstract: A tire air pressure monitoring apparatus includes a plurality of transmitters provided in respective tires on a vehicle and a receiver mounted on the body frame of the vehicle. Each transmitter radio-transmits data regarding the internal air pressure of the associated tire. The receiver receives radio-transmitted data from each transmitter. The receiver displays the received data on a display and stores the data in a non-volatile memory. When a request signal from a predetermined external communication apparatus is received, the receiver radio-transmits data stored in the non-volatile memory to the external communication apparatus. This allows various kinds of data such as air pressure data to be easily loaded from the receiver to the external communication apparatus.

Abstract: In detecting which transmitter of several of transmitters has transmitted a radio signal based on digital data from an RF circuit, a main controller of a receiver consecutively sends activation commands to each of several control circuits such that only one of the control circuits is activated at a time. The main controller detects which of the antennas corresponds to the control circuit that was activated when the voltage level signal from the RF circuit was lowest, and judges that the detected antenna is closest to the transmitter that transmitted the radio wave. As a result, the power consumption is reduced, and the transmitter that transmitted the radio wave is accurately detected.

Abstract: A tire air pressure monitoring system includes transmitters and a receiver. The transmitters wirelessly transmit data regarding the inner pressure of tires and the receiver receives the data from the transmitters. Each transmitter has its own ID code and includes a pressure sensor for measuring the inner pressure of the corresponding tire. Every time each pressure sensor measures the pressure, the corresponding transmitter generates a time interval by performing a pseudorandom number calculation based on the measured pressure and its ID code. The pressure sensor will measure the pressure each time the obtained time interval elapses. When each pressure sensor measures the pressure for a predetermined number of times, the corresponding transmitter wirelessly transmits data. This system prevents the transmitters from interfacing with one another and facilitates the manufacture of the transmitters.