Microwave Doppler Radar Sensor for Motion and Speed Sensing ...

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Testing Motion of peopleOutput when room is having motion of people.No output where there is no people in room.4Sunrom Technologies Your Source for Embedded Systems Visit us at www.sunrom.com
Introduction to Working PrincipleThe Doppler Effect has been characterized for a long time now, when it was first observed for soundwaves. This effect has been used for very practical purposes by applying it to electromagneticwaves. It is a very useful way to determine speed along with other applications in a system. Thisapplication note will go over several ways to implement Doppler radar in a way that is useful for aparticular system.BackgroundDoppler radar uses the same principles discovered by Christian Doppler when observing sound andapplies them to electromagnetic waves. In general, the Doppler Effect is a shift in frequencyperceived by a receiver from a signal source due to relative movement of the source and/orreceiver. The most obvious way to see how this can affect electromagnetic waves is howastronomers use the color shift from light waves travelling from astral bodies to identify the speedthese objects are moving away or toward the Earth. For a Doppler radar system, a known frequencysignal is transmitted from an antenna which is pointed at a reference object. A separate antenna isused to receive the signal that is reflected back from the reference to measure the Doppler shift ofthe signal.The basic formulas used from here are as follows:Here fr is the received frequency, fo the source, vs relative speed of the source, vo the observerspeed, and v the speed of the waves in the medium. For practical purposes the difference infrequency is used for calculations.Here is the block diagram of sensor, Note theOscillator is 10 GHz and Mixer gives output asper difference in frequency between transmittedfrequency and received frequency. If there is nomoving objects the oscillator and receivedfrequency will be same and the output will bezero. If there is difference in frequency the outputwill vary.ImplementationA simple Doppler module, can be easilyintegrated into multiple types of systems forvarious purposes. Doppler modules have aninternal oscillator used to produce the signalfrequency transmitted as the source. Thereceived signal is then mixed with this set signal,which produces an output that is a sinusoid containing the frequency difference between the outputand receiver signals. In most systems, these values need to be recorded or read in a tangible wayand this is usually done with some sort of microcontroller. The easiest way for a microcontroller toread data from an analog device is if it outputs a DC level voltage. That is what the sensor outputs.5Sunrom Technologies Your Source for Embedded Systems Visit us at www.sunrom.com
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