Time Interval Measurement

Discussion in 'General Electronics Chat' started by eray, Apr 1, 2010.

  1. eray

    Thread Starter New Member

    Mar 31, 2010
    hi, i am new to this forum and glad to be here :)

    i am planning to make a laser rangefinder project, which measures time of flight for laser pulse. and need your help about electronics part of it.
    as i know, i should use a time to digital converter, which is triggered by laser pulse and stopped with reflected beam. the system should be fast enough to give error not exceeding 10 cm in measurements.

    what are your suggestions about the circuit? thanks :)
  2. russ_hensel

    Distinguished Member

    Jan 11, 2009
    This is not easy you need nano second ( giga hz ) response for resolution to the nearest 30 cm. This is very high frequency for a hobbiest.
  3. iulian28ti


    Dec 4, 2009
    Last edited: Apr 1, 2010
  4. someonesdad

    Senior Member

    Jul 7, 2009
    Russ is right, as I learned to my own chagrin a number of years ago when I thought this would be a neat project. The speed of light is 3e8 m/s or 3e10 cm/s. To measure to 10 cm, you need to resolve time to 10/3e10 s or a third of a nanosecond.

    You might want to research the techniques of how modern laser distance meters measure distance (it's based on comparing signal phase). However, it's likely that even this technique would be beyond the skill of the average hobbyist.

    Instead, go to Amazon and type in "laser distance meter" and you'll see a number of offerings in the $100-$150 range. They've come down in price quite a bit in the last year or so because of the competition. I got the Bosch DLR165K as a gift a year or two ago. I'd like to wring the neck of the product marketing engineer who designed the feature set, as they made some terribly dumb choices. But still, the device can measure to within around a mm to distances around 50 m (but it works poorly in direct sunlight). It's an incredibly useful device and my wife even comes in and borrows it occasionally. It's also a superb tool for taunting two of our four cats -- they often will sit in the corner scanning the ceiling looking for that strange point of light moving around (they know it lives up there, yet it comes down to the floor where they can chase it). :p
  5. eray

    Thread Starter New Member

    Mar 31, 2010
    thanks all for your replies. if you have a brief look to the following article, you can have an idea about what i am trying to do. http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=00650815

    i want to use the same system of commercial laser range finders. i dont have problems at laser, sensing points and calibraiton. since i am a physicist, electronics part seems more difficult to me.

    as i made some research, found an integrated TDC (time digital converter) chip with better accuracy than my demands: http://www.acam-usa.com/GP1.html
    this can be used and has a LabVIEW software (i am using labview data acquistion).
    i may try to use it, but if there are simpler systems with less features, i can use them for TDC part.