Photodiode Vs LED to sense laser light presence.

Discussion in 'The Projects Forum' started by Wayne7711, Aug 6, 2013.

  1. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    Hello all, I am new to the forum.

    I have a project I am working on which requires me to create a 3 inch by 3 inch square area that when a green laser light is pointed anywhere within the 3 by 3 square a signal of 5 volt min to 24 volt max will be sent to a plc.

    Is such a circuit possible?

    If so could someone explain to me how this can be achieved.

    I have tried using the circuit shown on Robs Robot room which uses photodiode's but would not work in sunlight, indoor light, and dark.
    This is a requirement of what I'm trying to achieve.

    Any help would be greatly appreciated.

    Regards,

    Wayne
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Is the laser light modulated in any way?

    You have to detect it if it falls "anywhere" in the 3"x3" area? At any angle, too?

    Any bounds on the intensity of the laser?

    I understand the photodiode, but how were you planning to detect the light using an LED, as indicated by the thread title?
     
  3. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    For now I am going to say no, the information I have on the laser is that it is 5mW max 532nm wavelength.

    As far as using LED instead of photodiode I have in the past reversed the poles of an led to act as a kind of of receiver.

    As far as the angle question,

    The laser would come from a head on position but may also come in from slight angle on either side.

    As to the 3x3 area, it needs yes it needs to be detected in a 3x3 flat surface on one side.
     
    Last edited by a moderator: Aug 7, 2013
  4. WBahn

    Moderator

    Mar 31, 2012
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    Leaving aside the issue of seeing a green dot of low power light in bright daylight aside, being optically sensitive of nine square inches seem rather challenging in and of itself.

    The low tech way that comes to mind is to point a camera (cheap webcam-type imager) at the region and use software to look for the laser dot.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    If the laser signal is modulated, I wonder if a simple 3x3 solar cell might pick up enough signal.

    How do those laser tag vests work?
     
  6. Shagas

    Active Member

    May 13, 2013
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    hmm I'm also curious as to if it would work because I need a sensor for my alarm project which has a wider area than a simple IR photo diode
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Using wayneh's solar cell suggestion, just now tried a 2 in. X 2 in. solar battery, rated 3V, with red 3 mW laser. Inside bright, 1.05 V, with laser, 1.14; inside with red filter .86V, laser 1.05V; dark w fltr. .o3V, laser .38V. Position of spot made no difference. Modulate laser & prob. would be detected outside.
     
  8. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    In reply to Wayneh,

    Your question about the laser tag function, I have looked into this and I believe that the laser part of the game is not really a laser but a unit that emits an pulsed ir signal like a remote control. I have looked into this quite extensively and that is what I found out.

    I tried the solar cell option as well but was not able to make it work, this is not to say that it will not be able to work, but my lack of knowledge of electronics has hampered my ability to further that course, I'm learning as I go.

    I have a degree in mechanical engineering and have worked with machine control logic, so When it comes to sensors I am learning as I go.

    I was told this was the site for asking questions about circuits and from what I have seen so far I'm sure you folks can help me.

    I have made a board that worked in everything but intense sunlight. I will take a photo and list the components so that you may get a better idea and hopefully put me in the right direction as to what I'm doing wrong.

    My circuit worked on the bread board but when I made my own board it did not work.

    As well I will copy my circuit so you can look at that as well.

    Thanks to all who are looking at this for me and I hope you can help.

    Regards,

    Wayne.
     
  9. Shagas

    Active Member

    May 13, 2013
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    By "my own board" you mean a soldered PCB or prototype board ?
    If so , then maybe you fried a component by overheating it
     
  10. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    Reply to Shagas,

    As to making my own board yes I did make it using the photo etching method,
    I am in the process of posting the schematic and physical board.
     
  11. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    Before I get to the details of my board, I would like to say that the program I used to design the circuit crashed, I thought I had save the file but I lost it, All I have right know is the photo copy on clear overhead projection paper.

    I removed the chips from the breadboard to solder them to the pcb. I can hear the moaning from all of you now, document your work document your work, It was late and I failed to do this,


    I'll now explain my circuit. I am working with 9 led's wired in series, running them through a resistor mesured at 55,7 resistsance on my meter. then they go into a compairator chip . Then I am running what I call a ambient light led. My theory is that when both the ambient light led and the led reciever array is exposed to the same light source the compairator chip will split the voltage and when the led array is hit by the laser it will see this and forward the out put voltage to a relay which in turn will send voltage signal to my plc as an input.

    Now I am using the method of reversing to poles of an led to act as a reciver. I have large led's which were given to me that have a dome over them that gloow when the led is hit by the laser.

    Through testing I found that if I take an led and encase it in clear epoxy the whole block glows green as the laser is bouncing off the inperfections and miniscule airbubbles it makes the whole block glow and the leds recieve this light and provides enough current for the compariator chip to see the voltage change.

    The compairator chip is LMC6482 the relay is LBA716 I dont have the refernce number on the led but they are showed in the photos.

    Please any further information needed please let me know.

    Forgive me I'm trying to figure out how to post pictures.
     
  12. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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  13. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    The top left chip in the circuit design is the relay the chip in the right of the photo is the comparator,

    There is a 24 volt to 5 volt dc converter chip in the circuit but I removed it and applied the 5 volts to the relay as I found that the converter is bad.

    I am looking at the circuit now and trying to figure where i made the mistake,

    I clearly made the mistake as It worked fine on the bread board. Maybe I reversed the connections when I photo etched it on the board.

    I'm about ready to start over as that may be the best way,

    Any suggestions would be appreciated.
     
  14. Wayne7711

    Thread Starter New Member

    Aug 6, 2013
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    Shagas,

    I am using a Weller Model WES51 soldering iron, I have it set to 65 and am using flux.

    Is it possible that this setting is to high? When I solder I am using flux and the tip is only on the solder pad for a second or two.
     
  15. Gigantos

    New Member

    Mar 15, 2012
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    I would like to ask a fast question, I don't belive it is very complex, I made an extremely simple circuit, to use a photoresistor as a laser detector, this might be the wrong place to ask, but im giving it a shot, the "laser" im using is just a 3 dollar wal-mart laser pointer, I took a photoresistor, out of a grab bag from radio shack, and a blue LED, and a variable resistor, I put the variable resistor in line with the photoresistor, then to the positive side of the led, and the other side of the LED to ground, its using +12 volts, only because im using a +12 volt adapter, that was lying on my work bench already, I have no target voltage in mind, all its intended to do is latch an SCR, or maybe just a pnp-npn combo, I just wanted to ask if anyone has a better idea, it works but the main problems are, I cant get the photocell, acclimated to ambient indoor lighting, so it was always on, covering it with black electrical tape fixed that, the LED turns on, and then bleeds back to off, VERY slowly, so I know im getting current leakage thru the resisters, my first guess is the 12 volts, im going to give 5 volts a try in the morning, but I was wondering if anyone might know of a simple and fast alternative, I have a IR emitter/receiver, and I tried using the receiver in place of the photocell, with no luck, I have done a lot of google research and all the circuits I come up with are either to complex for what I need, or use 2 photocells, im planning on only using one, for a pulsed on-off, anyways, just wondering if anyone might have any helpful hints, you don't necessarily need to draw/type out any schematics for me, just a helpful nudge in the right direction would be great, sorry for rambling so long lol =), also, this is for an extremely low tech project, so it doesn't have to be great, just so it stays off in ambient room lighting, no more intense than the lighting in a normal home lol, I also played with a comparator circuit, to just read the ambient light as a baseline, and the laser would be the trigger, but I need to build about 50 of these, so the more simple and the cheaper the better.
     
  16. wayneh

    Expert

    Sep 9, 2010
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    1. You should start your own thread rather than reviving and hijacking an old one.

    2. Read up on grammar and punctuation. Throw us a bone and use a period now and then.
     
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