Speed Radar Questions

[mherupineda]

Hi, I'm new here  i had a small project regarding measuring the speed of vehicles so i had to create a speed radar just like those speed radar signs on the road. What i'm doing now is creating a speed radar circuit which is for experimentation only. I had used a GH-100 Microwave Doppler Sensor and had able to interfaced it on arduino using the frequency library.

What i want to ask for those who had created or experienced how the speed radar works is that, can the speed radar detect a car which is behind it (even its not on its cone detecting range)? And if it detects the speed of a car that is reversing towards the back of the speed radar?

Example, we have a road and it has two (2) directions which is x and y, let's say x-direction is towards east and y-direction is towards west. Theres a speed radar sign perpendicular to the road and it is facing on x-direction (east) meaning it now measures the speed of cars coming from x-direction going y-direction.

My question means, Can the speed radar detect the speed of the car that is coming from the y-direction (west) going x-direction (east)? And can speed radar detect the speed of the car that is in reverse-mode coming from y-direction going x-direction?



I hope you can help me. React please if you had an idea with these. Thank you very much.

[robtillaart]

> can the speed radar detect a car which is behind it (even its not on its cone detecting range)?
No,

> And if it detects the speed of a car that is reversing towards the back of the speed radar?
No,

>  Can the speed radar detect the speed of the car that is coming from the y-direction (west) going x-direction (east)?
yes

> And can speed radar detect the speed of the car that is in reverse-mode coming from y-direction going x-direction?
yes

but as the answers above will probably trigger more questions,
please study the theory how Doppler radar works here - https://en.wikipedia.org/wiki/Doppler_radar

[mherupineda]

> And if it detects the speed of a car that is reversing towards the back of the speed radar?
No,

> And can speed radar detect the speed of the car that is in reverse-mode coming from y-direction going x-direction?
yes

but as the answers above will probably trigger more questions,
please study the theory how Doppler radar works here - https://en.wikipedia.org/wiki/Doppler_radar

Hi Sir,


      Thank you very much for the reply, i had already study the theory of how Doppler radar works that's why I'm confused on the output of the sensor i had made. The circuit i had made was the example on its datasheet which is a continuous wave circuit and my code on the arduino is like this:

Code: [Select]



#include <FreqMeasure.h>

 int count=0;
 double sum=0;
 
void setup() {

 Serial.begin(9600);
 FreqMeasure.begin();
 Serial.println("Frequency Read Begin");

}


void loop() {

   if (FreqMeasure.available()) {
      
   sum = sum + FreqMeasure.read();
   count = count + 1;
  
       if (count > 30) {          // average 30 readings together
    
           float frequency = FreqMeasure.countToFrequency(sum / count);
          
           float speedValue = frequency / 19.49;            // from the formula Fd = 2V(ftarget/c)cosTheta
                                                                          // where V(km/h) = Fd/19.49 and V(mi/h) = Fd/31.36
           if (speedValue < 1.00) {
      
                Serial.print(frequency);
                Serial.print(" Hz  ");
      
                speedValue = 0.00;
      
                Serial.print(speedValue);
                Serial.print(" kph ");

           } else {
      
                Serial.print(frequency);
                Serial.print(" Hz  ");
                Serial.print(speedValue);
                Serial.print(" kph ");
      
           }
        }
    
    sum = 0;
    count = 0;

    }
}



      The output i had after seems fine (though i had yet to buy a tuning fork) when i applied it practically on the road, when theres a car in moving in reverse towards the back of my sensor, it sense a lot of frequency, greater than the frequency of a moving car heading towards the front of my sensor (detecting range of the sensor).

       i had search studies but what i experience seem hadn't happened on others (that's why i even like to see a true speed radar on the road, and test some activities to see output. Dumb luck but theres no any speed radar on our area). Any explanation sir?

[robtillaart]

do you have a link to the datasheet of the GH-100 Microwave Doppler Sensor ?

[mherupineda]

do you have a link to the datasheet of the GH-100 Microwave Doppler Sensor ?

thank you for the reply, http://pub.ucpros.com/download/GH100Datasheet.pdf?osCsid=vs1q4b4cdvohrm5i2ls257ts80 here's the datasheet link sir.

[MarkT]

Doppler radar cannot sense forwards v. backwards, only the absolute value of the component of velocity
along the light-of-sight.  Remember than all metal objects reflect radio waves and radar works most reliably
in open terrain with no radio-reflecting surfaces other than the vehicle you are measuring.  You would expect
erroneous behaviour in a crowded urban environment for instance.

The other thing is the radar gun must be stationary during a measurement, you mustn't move it
or you'll get lots of artifacts from the speckle pattern.