# Understand and use of speed sensor module for a project

Discussion in 'The Projects Forum' started by ord6, Jun 9, 2014.

1. ### ord6 Thread Starter New Member

Jan 24, 2014
9
0
Hello,

For a project I need to connect a speed sensor module with an Arduino Due and calculate the speed of an approaching object.

the sensor is:
http://www.limpkin.fr/index.php?pos...lectronics-for-a-\$7-USD-doppler-motion-sensor

From what I understand the sensor already output a signal that its' frequency represents the speed of the object.

I would really appreciate any help understating the module operation, and how can it be connected and operated by the Arduino.

If more details are needed I'll be happy to supply.

Thanks.

2. ### sirch2 Well-Known Member

Jan 21, 2013
1,008
351
Google "Doppler RADAR" you will get quite a lot of info.

Basically it sends out a radar signal and receives the return signal that bounces off an radar reflective object, such as a car. If the car is moving then the frequency of the returned signal will have been changed by the doppler effect - for a car moving towards you the frequency will have risen a little because the velocity of the car "compresses" the reflected wave.

The transmitted and received signals are mixed together and what you get out is the difference between the two which is a frequency proportional to speed.

3. ### ord6 Thread Starter New Member

Jan 24, 2014
9
0
Thanks for your reply.

I understand how the sensor calculates the frequency, what I need help with is how to use it with Arduino, how to operate it and get the signal in the Arduino?

Thanks.

4. ### sirch2 Well-Known Member

Jan 21, 2013
1,008
351
So you want a frequency counter? One approach is to use a comparator. I guess you would need to amplify up the output from that module to a reasonable level, then pass that to a comparator set to a level of say 80% peak output from the motion detector. You can then use the comparator output to drive a pin on the Arduino and count the time between low/high transitions.

Jan 24, 2014
9
0
6. ### sirch2 Well-Known Member

Jan 21, 2013
1,008
351
Sorry but I don't have time to design your project for you. I may be wrong but from a brief skim of the page you posted it says

He then goes on to give an amplifier/filter design.

As for the rest look up comparators, try googling "arduino comparator" and "arduino frequency counter"