Making a distance and speed Doppler effect based sensor module

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Navneeta Deo

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Hi guys, I am in urgent need of help.
I have a Doppler effect based sensor module and wanna use it to measure sped and distance of moving object.The output of sensor is IF signal but I don't know how to process this signal to get information about doppler shifted frequency . That would help me to know speed and range of target. I am new in this field. Any help is really appreciable :smile:
 

How about giving a better clue as to which "Doppler effect based sensor" you are using, so we can look-up the datasheet. Alternatively, you could post a link to that datasheet.

John
 
The output of usual doppler modules is "zero-IF" as the received signal is mixed with the carrier itself. You have either single or dual (quadrature) outputs.

The object speed is directly proportional to the output frequency. With a quadrature output, you can also detect the direction of movement. There's no distance information, the doppler signal level tells you about the radar echo strength which can be related to distance for known object size.
 

Hey, its a Frequency modulated continuous wave radar. Not much info available on datasheet. But u can see d application note . Here it is :smile:
 

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  • Application-Note_Radar-Sensing_E_BBsensors.pdf
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You forgot to mention FMCW. It's not actually using the doppler effect.

FMCW does allow a distance measurement.

There's a lot of FMCW literature on the web. Here's a good company brochure
**broken link removed**

P.S.: bb-sensors has many radar modules that are using fixed frequency (doppler) method. Are you sure that your module is supporting frequency modulation?
 

hi, thanks for the brochure. Yes I am sure my module supports Frequency
modulation.
 

FSK is easier to get distance for moving object. With FMCW you will need a huge sweep bandwidth, and also your doppler frequency will be added to distance frequency, and i did not see successful products use FMCW nowdays, only tons of papers "oh, we solved the problem!". FSK or MFCW (multi-frequency cw) is a better choice. Use FMCW only if you sure how to process it with doppler inside, not just beat frequency.
 


Hi, thanks for ur suggestion.:thumbsup: Now I just have FMCW type sensor . If I just need to measure speed of target, Can you suggest some methods/example circuit to process the output signal All I know I need to use a preamplifier circuit . Also, what do you mean by the last line in your comment " To be sure to have doppler inside , not just beat frequency" :roll:
 
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Range is a 4th order path loss from 2 directions, so CW requires huge Tx rejection by directional coupler and tracking notch filter in DSP of the IF signal. Burst mode wavelet has significant advantage in CNR or SNR result by time multiplexing Tx & Rx.

Range is always time delay of burst or phase shift of CW of a stationary reflector, which can only be seen on short range directional couplers.

Velocity is always the derivative of phase or delta frequency of received .
Direction controls polarity of relative frequency shift and phase noise must be very low in LO since derivative function boosts noise proportional to frequency difference.

LO rejection, phase noise, noise figure of Rx and phase noise of carrier are all critical for optimal lowest possible detection threshold.

VNA or really good SA skills with directional couplers are critical to improving design.
 


Hi, the specs are here:Sensor module must be able to detect a stationary object or moving vehicle having speed upto 100 km/hr.
Sorry, for the distance measurement spec. Its not required actually.
I am trying to use op-amps to amplify the output signal coming from the sensor.But I am not able to understand how can we get information about speed of target. What sort of circuit should I useto process the signal.
 

search for any patent on this topic, for example on freepatents.com or google, 99% of such systems use FFT(fast fourier transform) of signal from sensor. Are you really need to detect stationary object? What is maximum distance?
 

Using a microcontroller as period counter and speed detector

Hi, I want to use a microcontroller to detect period of a signal incoming from a sensor circuit . The microcontroller should detect a frequency of 4320 Hz of the incoming signal and then able to tell us the speed of the object. Can anyone explain how to use the microcontroller for this purpose? Also which microcontroller should we use?
:roll:
 

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