help in speed detector

Discussion in 'The Projects Forum' started by useless0, Jan 6, 2011.

  1. useless0

    Thread Starter New Member

    Jan 3, 2011
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    We are working on an overtaking inhibition system. So I need to find out the speed of the vehicle in front. From the relative speed we can decide whether braking has to be applied or not. I rejected doppler shift being too complicated. I just thought of ultrasonically finding distance to vehicle at the front and then doing so after some time. If the distance is lesser, it means our speed is more and braking has to be applied. What I need is advice on hardwares I can use and if possible, a circuit diagram. The project is done on PIC 16F873 and software is not a problem, but circuitry is.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You may find that the range that an ultrasonic detector can operate at highway speeds is way too short for safety. You may have no choice but to use radar.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Sound waves in an "acoustically impaired" environment, such as highway speeds, wouldn't work with any range beyond maybe 10 feet, 20 at the limit.

    The transducer would be at the front of the car, by definition, which is where a whole lot of wind, wheel/tire, engine, and other sounds would greatly decrease the signal to noise ratio. Inclement weather such as rain or snow would take a bigger toll.

    Radio seems to be the only option for the speeds and distances you are looking for.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Are you working on subsonic UAV's or kiddie carts?

    How about a little more information, like what sort of distances are involved, precision needed, why you rejected Doppler, and is the ultrasonic method you envision determining distance by TOF or triangulation? Have you considered using laser?

    John
     
  5. John P

    AAC Fanatic!

    Oct 14, 2008
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    You might possibly be able to use an optical rangefinder system rather than radar. There are some designs aimed at the robotics market that claim to work well enough for vehicle guidance but I'd never trust my life to one on the road!
     
  6. beenthere

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    One thinks of splattered insects, mud and ice, none of which degrade radar like an optical sensor. The day/night difference in sensing with optical might be a challenge.
     
  7. useless0

    Thread Starter New Member

    Jan 3, 2011
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    thanks, now I have to convince my fellow group mates. So, the radar gun using doppler shift as with optics night-time is a problem. i found one one this forum, but I found it highly complex involving DSP and stuff. Anyway could I get something on internal circuitry of radar guns. I've been trying a lot, but I guess not at the right places.

    Well, what range is the wave, how much will the transceiver cost.
    I think it is Ghz range. After getting back the wave, we subtract the parent wave from it then ......
     
  8. bertus

    Administrator

    Apr 5, 2008
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  9. beenthere

    Retired Moderator

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    Weirdly enough, there are any number of baseballs available with speed sensors inside. Some say they use radar. Here is a link to a number of such things - http://www.nextag.com/speed-sensor-baseball/products-html

    You might be able to dissect out the circuitry and make use of it.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I am a slow reader. Which ones said radar?

    Or, was it these that threw you off:

    [​IMG]


    John :D
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Accelerometers + known mass = speed.
     
  12. beenthere

    Retired Moderator

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    Some claim to use radar, some lasers.
     
  13. useless0

    Thread Starter New Member

    Jan 3, 2011
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    to buy a product and dissect it is tough. We do not have that much budget. What I want is atleast a description of a circuit for speed detection.

    Let's say I use a mixer and get the difference frequency. I guess I could do with an ADC, and then find the frequency of it by some counting mechanism and then compare.
    The problem is that I'm just an undergraduate student with 0 experience (maybe -1).

    Will that do.................?
     
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