# Radar based motion and speed detection module

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Hi guys,
I am designing a Radar sensor module which can detect speed of objects upto 100 km/hr. I have a sensor whose output is an IF signal. But the output voltage is quite low, only upto 300uV. I need to connect a preamplification circuit in order to make the output signal usable. The amplifier circuit must have gain of 80 dB. Any help is appreciable.
Thanks!

#### GopherT

Joined Nov 23, 2012
7,983
How will you emit the signal? How will you detect the signal?

#### alfacliff

Joined Dec 13, 2013
2,449
since you dont specify what the if frequency is, its a little difficult. if its a speed (dopler) radar, the output is probably audio frequency, and there are plenty of audio preamps and circuits available, both transistor and opamp.

#### Lestraveled

Joined May 19, 2014
1,943
What is your IF frequency? Will you be doing Doppler processing?

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Yes its a Doppler based Radar. The output is Intermediate frequency signal. According to the datasheet I have for my sensor, it says the output can't be more than 300 microvolt. So, I need to use amplifier circuit. Thanks for your suggestion about the amplifier circuit. A liitle more detail would be welcome(as in I have to use low frequency amplifier with 80 db gain with low noise characteristic).
Also, I am facing a problem in understanding how can I test my circuit on simulation tool like Tina or LTspice. All I know is that output of sensor can't be greater than 300uV. So, I think to use a voltage source of 300uV succeeded by amplifier circuit.In that case how do I measure speed of the moving object just by knowing voltage(and not doppler frequency). For your information , doppler frequency is related to speed as:
F.D.= (2f*v*cos a)/c
where c= speed of light
a=angle between actual direction of motion and connecting sensor object
v=velocity of moving object
f=transmitted frequency
F.D.= Doppler frequency
Please help. I am a beginner in this field !

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Yes its Doppler based Radar. The transmit frequency is 24 GHz . I don't know about the IF frequency(doppler shifted frequency) but the amplitude of IF signal(sensor output) is 300 uV

#### alfacliff

Joined Dec 13, 2013
2,449
the voltage will not be affected by the speed, other than distance. the frequency is shifted by the doppler effect that type module mixes the transmitted frequency with the reflected frequency. the formula should be on line somewhere, has to do with distance change in wavelengths per second.

#### Lestraveled

Joined May 19, 2014
1,943
How can anyone assist you with an amplifier if you do not know what frequency you are working at?

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
I get your point. But the frequency of the Intermediate Frequency (IF) which is output from sensor is not provided in the datasheet and I dont know how can I find it. I am posting the application notes here for my sensor that I am using. Hope it gets clear here!

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#### AlphaDesign888

Joined Jul 27, 2014
189
I get your point. But the frequency of the Intermediate Frequency (IF) which is output from sensor is not provided in the datasheet and I dont know how can I find it. I am posting the application notes here for my sensor that I am using. Hope it gets clear here!
Just all for the hell of it, or are you planning to make an product sell it and make some money?

#### RichardO

Joined May 4, 2013
2,273
F.D.= (2f*v*cos a)/c
where c= speed of light
a=angle between actual direction of motion and connecting sensor object
v=velocity of moving object
f=transmitted frequency
F.D.= Doppler frequency
Have you actually done this calculation? See post #3 by alfacliff for a hint as to what to expect.

Also re-read the paragraph at the top of page 8 of the application note. I think the use of the term "IF" is misleading. The output signal is an intermediate frequency only in the sense that it is the result of mixing the transmitted and received signals to create a difference frequency.

#### GopherT

Joined Nov 23, 2012
7,983
You will have to calculate the Intermediate Frequency based on the range of speeds you wish to detect and your sensing frequency. As said above, the transmitted signal and doppler-shifted echoed signals (from moving object) will mix and you will then get the intermediate beat frequency that you will need to amplify and count, then process to get back to a speed.

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Hi, the maximum doppler frequency will be 4443 Hz @ max. speed = 100 km/hr. Knowing this , does that mean I need to use a preamplifier circuit followed by a frequency counter to know the speed of moving vehicle.

#### Lestraveled

Joined May 19, 2014
1,943
I have never seen a frequency counter used in this kind of system (too slow). There are two methods of processing that I have seen:
1. Software method - Amplify, digitize and then do a Fast Fourier transform or FIR filtering.
2. Hardware method - Filter banks with threshold detection.

#### AlphaDesign888

Joined Jul 27, 2014
189
You could probably get some better answers down at the Police station.
Since they have been using this technology for years now to detect speeding drivers.

#### AlphaDesign888

Joined Jul 27, 2014
189
Be careful how you go about asking them though.
They might drive you to an mental hospital.

#### RichardO

Joined May 4, 2013
2,273
Hi, the maximum doppler frequency will be 4443 Hz @ max. speed = 100 km/hr. Knowing this , does that mean I need to use a preamplifier circuit followed by a frequency counter to know the speed of moving vehicle.
OK, so the maximum frequency you need to amplify is about less than 5 KHz. What is the lowest speed you want to measure and what frequency would the Doppler frequency be for that speed?

Your want your amplifier to have a bandpass from the lowest Doppler to the highest Doppler frequency. The narrower the bandwidth of the amplifier, the lower the noise.

What you need is essentially an audio amplifier. You could try an microphone preamp for initial testing. It will limit your minimum speed to about 1/2 km/hr. I doubt that this is a problem. The may want to add a low pass filter to reduce the high frequency bandwidth.

If the microphone preamp is not good enough then you will have to design a custom circuit using a low noise amplifier and a bandpass filter.

Because the frequency is low, a period counter may be better than a frequency counter. A standard frequency or period counter will not display the speed in k/h. A microcontroller normally used because it does both the period counting and conversion from the period measured to speed for display.

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Hi, so that means : a Microphone preamp , a low pass filter folllowed by a microcontroller should solve my purpose. Can u suggest which microcontroller to use.

Thread Starter

#### Manjugolu

Joined Jul 31, 2014
16
Be careful how you go about asking them though.
They might drive you to an mental hospital.
Hi, I guess this forum is to help and share knowledge. As said before I am a beginner in this field, so it will be better that you don't provide help rather than putting comments to discourage someone's efforts.

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