Finding Distance with Laser

Discussion in 'The Projects Forum' started by Moin51, Oct 21, 2013.

  1. Moin51

    Thread Starter New Member

    Oct 21, 2013
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    Hey Guys,
    Can anyone guide me how can I design a device to measure just the distance between the object and the device through reflection, I have studied LIDAR GUN and it pretty much does what I want but I am unable to find any circuit diagrams for it. I need to know how can I make this device ?:confused:
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,791
    A shot in the dark.

    You modulate the light signal in some way so you can measure the transit time from the source to the reflector and return. Light moves approximately 1 foot per nanosecond. As long as you can measure nanosecond intervals you should be able to do what you want.

    Going out on a limb here, I'm going to hypothesize that this would not be a suitable hobby project. I could certainly be wrong however.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,126
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    You could go read some patents and do some reverse engineering of the commercially available products.

    Or you could just go buy one. ;)

    Is there a good reason to make your own?
     
  4. #12

    Expert

    Nov 30, 2010
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    It seems there is a certain percentage of people that see devices that have been through millions of dollars worth of research and development over the course of decades of time and think, "I can do that this week".
     
  5. sirch2

    Well-Known Member

    Jan 21, 2013
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    This - http://blog.qartis.com/arduino-laser-distance-meter/

    or this http://www.kickstarter.com/projects...ate-measurement-and-modelling-on?ref=category

    Generally the low cost units work by modulating the LASER light at a number frequences in the 10 - 100MHz range and measuring the phase difference of the returned light. By using multiple frequencies the actual distance can be calculated.

    Things like the avalanche photo diode needed to do this will cost you more retail than a cheap ready made unit from ebay.
     
  6. #12

    Expert

    Nov 30, 2010
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    Thanks. I was wondering if phase would work instead of trying to measure nanoseconds.
     
  7. CVMichael

    Senior Member

    Aug 3, 2007
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  8. wayneh

    Expert

    Sep 9, 2010
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    He didn't address an obvious problem with phase comparison: What happens when the reflected wave is an entire wavelength (or n wavelengths) behind? His device would read zero phase shift and therefore zero distance.

    Maybe he did something with the modulation to identify this situation?
     
  9. CVMichael

    Senior Member

    Aug 3, 2007
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    Yes, I was thinking the same thing, but in the short distance he was measuring, the wavelength did not overlap. I guess it is a balance between the frequency of the laser, and the distance when the receiver won't get any readable light back.

    If the frequency is low, this means less accuracy, and you can measure further until it overlaps or loose signal.

    So if you don't need high accuracy, and not high distance, you might not need to measure using multiple frequencies.

    What I love about that method is that you can measure hundreds of times per second! perfect for line scanning :) you put a spinning mirror to reflect the laser, and you get a laser scanner similar to these http://www.robotshop.com/ca/laser-scanners-rangefinders.html that cost thousands of dollars.
     
  10. CVMichael

    Senior Member

    Aug 3, 2007
    416
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  11. wayneh

    Expert

    Sep 9, 2010
    12,126
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    That is amazing, to cram such sophistication into that package. It's not hobbyist cheap (at least not to my thinking) but it sure is interesting. More here.
     
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