Understanding Smart Sensors - Nomads.usp

Transceivers, Transponders, and Telemetry 187IR sourceVideo I.D.cameraRadar gunDetectorComputerFigure 8.7 Remote measurement of vehicle exhaust emissions.measurement devices, including an extension of previously used police radartechnology, which typically has a maximum range of 800m.8.3.5 Remote Keyless EntryAvailable wireless remote control of door locks on vehicles is a step toward anautomatic driver sensor (ADS). The ADS will be able to identify that a specificdriver is approaching the vehicle and that the driver will require access and possiblycontrol settings different from those used by the previous driver. Today’sremote entry systems have either IR or RF sensors. One RF system, diagrammedin Figure 8.8, has a transmitter in the ignition key that is powered bya lithium battery [19]. The transmitter generates a frequency of about 41 or230 MHz when a switch in the key is depressed. The vehicle’s rear windowdefogger acts as the antenna. The antenna receives the signal, which is then sentto the receiver for amplification, FM detection, and wave modification. If thetransmitted code matches the stored code, the motor drive circuit eitherunlocks or locks the doors. The wireless system can be activated within 3 ft ofthe vehicle. It has a standby mode, which is intermittent to avoid excessivedrain on the vehicle’s battery. If 10 or more incorrect codes are transmitted tothe receiver within a 10-minute period, the system reacts as if a theft is occurringand all reception is discontinued. The key must be inserted manually toverify ownership.