Laser receiver / detector

Discussion in 'The Projects Forum' started by NewbieDoug, Feb 4, 2012.

  1. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Hi.
    I use a rotary laser level for earthmoving- levelling house / shed platforms etc. Its wavelength is maybe around 600nm? Spinning freq prob abt 5 per second. All of the laser receivers I have ever seen detect the beam, and only give an output reading of Led's- High, On grade, Low. This can be very annoying when you would like to know HOW 'High' you are. I'd love to make a circuit that has a vertical line of photo diodes(?) (a foot tall) and just have a LED light up beside each photo diode? Laser beam strikes down the bottom, LED down the bottom lights up, etc. I assume I'd need a circuit that registers the pulsing of the striking laser beam, to differentiate it from ambient light. I also assume this topic has been previously discussed, Any chance of some assistance please?
    I'm not very SWITCHED ON, in offering circuit advice please consider me as uneducated. (Wife laughing in background..)
    Thanks!
    :confused:
     
  2. Geoffr67

    Member

    Dec 5, 2011
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    Interesting project, Ill be watching this thread.
     
  3. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Thanks. As I said, It REALLY annoys me that receivers that I have seen give such a 'binary' output. You can buy 'machine' receivers, about 200mm detecting height, to attach onto your machinery, but usually all you get is THREE lights. If you are lucky, you'll get a Rather High light, then that light blinking for bit high, then green middle light on grade etc. It would be SO excellent to just have a vertical line of leds to show exactly where the laser is striking the receiver, then you'd know EXACTLY how far off grade you are..
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A laser beam traveling @ 1 rev in 200ms, producing a 1/2 in spot @ 50 ft would be on target for only about 26 μs. Might make it difficult to modulate & detect the beam. Would it be possible to add a long focal length cylendrical lens to laser to slightly spread beam horizontaly, maybe 1 to 2 ft @ 50 ft? Seems like detectors would need to be spacer close enough so that beam would always strike one, so what is average size of spot? & working destances? I made a water drop detector with 4 ft between laser & detectors, 5 close spaced photo transistors to give a 1 cm dia target. Your project will need some thought- a real tough nut to crack.
     
    Last edited: Feb 7, 2012
  5. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Existing receivers read the beam with an accuracy of abt 5mm over 100m.
    Appreciating the help, but was assuming this idea would have been discussed previously and there might be links to an answer. Sorry, but calculating Trig is not the help I was looking for sorry..
     
  6. ifixit

    Distinguished Member

    Nov 20, 2008
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    Hi NewbieDoug,

    Perhapes you could modify the existing detector device so that it moves up or down a rod by a motor to "find" where the laser beam puts the "on grade" light on. The distance between where the detector now sets and the previously set reference marker, would be your visual indication of the amount off grade.

    An electronic circuit could use the 3 (high, on grade, low) LED outputs from the detector to drive a motor and determine which direction to search in and when to stop.

    Regards,
    Ifixit
     
  7. goodken

    New Member

    Feb 6, 2012
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    I made a water drop detector with 4 ft between lasor & detectors, 5 close spaced photo transistors to give a 1 cm dia target.[​IMG]
     
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  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Not simulated, not tested, just a suggestion: A bar graph display might be easier to read, & would allow repeating colors, say blues for below grade & red side for above grade. green for right on. FIG 1 shows one detector, first below center. C1-R2 adjust comparator trip point to compinsate for ambient light. D1-C2-R4 form a pulse stretcher to make LEDs more visable. NTE232 is invertor, maybe sub with schmitt trigger invertor, to give a logic level for OR gates. LED A, not labled- tied to R7, comes on when beam is one notch below green LED. If beam is lower, say D, then A, B, C, & D LEDs are lit, forming a bar- graph. FIG-2 shows possibility of giving more coverage per detector.
     
  9. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Thanks ifixit, had considered similar previously, but it is a very industrial application, jerking around on rough machinery, I'm not keen to spend time on mechanical means sorry. I sincerely appreciate the different input, but I was really hoping to get some circuit help sorry.
    Benard, The bar graph idea would be fine, if it could be made to work I'd guess it might not be too hard to convert to singular LED illumination. I'm too uneducated to know if your schematic will work sorry. I found this forum and got a little too excited thinking there'd be an easy solution to my enquiry sorry.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Singular LED operation would save some parts. Would probably invert comparator output so as to use a MPSA14 to drive LED. What would you suggest as detector spacing?
     
  11. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    5 x 5mm in the middle, then spreading out to 8-10mm towards the ends, total height maybe 300mm. Maybe some sort of dwell in led illumination for 1sec?
     
  12. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Uh, by singular LED, I mean ONE LED illuminated at EACH photo-diode/transistor..? And it needs to be able to detect the laser beam from 360degrees, so I'll make it with 4 vertical copies, 90deg to each other.
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    My cheap laser level makes a 5mm spot at 8 meters, what approx. size spot does your level make at say 50 m. Sensors need to be spaced close enough so that the beam strikes one, even if we use several sensors for ea LED. For 30cm bar, it looks like about 23 LEDs, 5 mm center, 20 mm at ends. Sensors, ie photo transistors, here, cost about $ 120 per 1000.
     
  14. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Laser is rotating, invisible to eye, detectors read accuracy of abt 5mm over 100m. 'Spot size' would prob be better worded as horiz line thickness would therefore assumable be small / narrow.
    If it helps any an example laser- http://lasertools.com.au/category537_1.htm
    Laser rotation speed / frequency of beam striking detector is more like 500rpm
    Can anyone please suggest other web places I could post my enquiry to get some suggestions please?
    Thanks.
     
  15. ifixit

    Distinguished Member

    Nov 20, 2008
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  16. Bernard

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    As to dwell time- no problem with one second, take neg. output from comparator and use to trigger 1/4 of 558[ quad timer ], output of one sec would rirectly drive LED.
     
  17. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    All previous efforts have proven unsuccessful in finding one on the market. Thanks for the link, but that LCD looks only a couple of inches tall. Those bar graphs must be ratioed to the beam strike height. I was hoping to make one, for less than $500+Freight, with a light/strike ratio of 1:1. I naively assumed it wouldn't be difficult to many electronics enthusiasts. I have appreciated all input, but I incorrectly assumed there would have been a quick easy answer.
    Thanks again.
     
  18. Bernard

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    If it would work, the simple ckt would cost about US $ 25. for active components for one 30 cm stick, photo detectors spaced 5 mm apart, 23 LEDs.
     
  19. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Which simple circuit please?
     
  20. NewbieDoug

    Thread Starter New Member

    Feb 4, 2012
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    Thanks all.
    So anyone got a complete circuit design suggestion please?
     
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