Measuring distance using RF module

Discussion in 'General Electronics Chat' started by indiansiva555@gmail.com, Jan 1, 2012.

  1. indiansiva555@gmail.com

    Thread Starter New Member

    Jul 24, 2011
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    Please give me some ideas on interfacing RF module with microcontroller for measuring distance. I would like to use this in my car for identifying the vehicle and measuring the distance between my vehicle and the front vehicle...
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I would say forget about the RF idea. What you want is Time-of-Flight measurements for an RF wave.

    The precision you will need cannot be achieved with standard components (say cheap).
    It will also require a lot of experience in the analogue AND digital AND RF domain.

    IMO an Ultrasonic range finder is a feasible solution, a long range up to a few hundred meters is certainly doable.

    Your own vehicles' speed would have to be taken into account though. According to AAC's ToS coupling anything to your cars' electrical system could not be discussed here. (if you want to discuss your system here you would need to measure speed with a GPS module for example)
     
  3. PaulEE

    Member

    Dec 23, 2011
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    Take a look at this...it isn't perfect, but it is rather interesting that they got something working:
    http://www.instructables.com/id/Distance-measurement-with-radio-waves/

    Otherwise, praondevou is right-on with the difficulty of time-of-flight measurements of RF. If you calculate the amount of time you've got for an electromagnetic wave to travel even one meter, and then compare that to the period of a typical 20 MHz microcontroller crystal (for example), you'll see why you don't have much headroom on those calculations and circuits...

    Now, if you don't need resolution and you only want ball-park numbers, you might be able to do something like the link above.

    As far as the car electrical system, "don't use it". "Use a 12v battery isolated from the car" so we can still talk about the project and can be reasonably certain that you won't blow anything up or hurt yourself...
     
    praondevou likes this.
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Cool link, really, I'm surprised it works with 5m precision (quite good for such a simple system and RF I would think).

    However, the OP wants to measure the distance between his vehicle and any others in front of his, i.e. I guess we cannot install something on the other vehicles...
     
  5. indiansiva555@gmail.com

    Thread Starter New Member

    Jul 24, 2011
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    That link helped me a lot, but does it require a transmitter and receiver at the other end also?...I am trying to make it by reflection properties of radio wave..
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    yes

    that's the problem. you would need a highly directional antenna, like a beam. Otherwise, how will you know where the signal was reflected at?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Understand we are talking RADAR in it's purest form.

    Thing is, this is not a project for a beginner, even the slightest.

    It could be done by an expert. It could even be done cheaply. It's not something I would care to try though.

    Schottky diodes are fast, they would be how you modulate the RF with a square wave. From there it is a matter of receiving the reflected RF wave and comparing the phase. All the components would need to be extremely fast, 1ns equals 9" one way. It is the speed that makes this extremely difficult to do.

    What is the frequency?
     
    Last edited: Jan 2, 2012
  8. SgtWookie

    Expert

    Jul 17, 2007
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    It would be difficult to obtain that kind of resolution even by an expert.

    Now, you could get 1 meter resolution if you could process the returns at ~1.2GHz, but even that would be mighty difficult. You would not be able to identify the vehicle.
     
  9. indiansiva555@gmail.com

    Thread Starter New Member

    Jul 24, 2011
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    Thank You experts..Is there any other way to identify the vehicle at a distance of 50m...
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    An object? Maybe. A car? No.

    There was an Iranian airliner shot down by the USA during the early 80 or 90's. The ship was a Pegasus class (I think) under attack by Iranian gunboats. The Iranian airliner was going to fly right over this ship at low altitude, the the ship could not tell what kind of airplane it was from just the RADAR, and the approach resembled an attack pattern. So a horrific tragedy happened.

    RADAR is very simple. It is not like vision, you are seeing a bounce of the radio beam. It is a dot on a screen most cases, nothing more.

    There are super sophisticated systems, like phase array RADARs, that are much more accurate. I suspect this would be out of your price range, unless you have a couple hundred mil in your pocket.
     
  11. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    If there was any expert here you would be ordering parts or building a prototype by now. :rolleyes:

    A Laser speed gun is another option (probably equally difficult to build for a hobbyist).

    You probably want to build something like this in your car I guess: http://www.youtube.com/watch?v=dlZEakHcD_o
     
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