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Re: [beam] Lasers

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  • David Buckley
    ... My opinion exactly. However in a real safety curtain it is something to be taken into consideration, so is a stray sunlight reflection. I do know what a
    Message 1 of 25 , Nov 4, 2011
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      > If some one wants that bad to get past one they will. If someone is
      willing to purposely try to by-pass the light curtain by pointing a light into the sensor then they deserve to have there arm ripped off.
      My opinion exactly.
      However in a real safety curtain it is something to be taken into consideration, so is a stray sunlight reflection.
       
      I do know what a laser is and what you propose isn't practically possible, it is silly to mislead people so.
       
       
      ----- Original Message -----
      Sent: Friday, November 04, 2011 9:55 PM
      Subject: Re: [beam] Lasers

       

      Mr. Buckley  there is no fail safe to definition of your standards. If some one wants that bad to get past one they will. If someone is willing to purposely try to by-pass the light curtian by pointing a light into the sensor then they deserve to have there arm ripped off. And if you look to the designs of say a ruby laser or semiconductor laser then you will see that a laser is just a light source placed within a semi reflective area creating an amplification before the light can pass through the output usually has a source to reduce the refraction of the light and keep it concentrated. We have though im afraid drifted off the topic at hand and this has now come to a dead end. thank you anyway for the help. 

    • Randy M. Dumse
      William Koepp said: Friday, November 04, 2011 4:55 PM ... Your original post said Any help would be much appreciated. DAvid was giving you very sound advice.
      Message 2 of 25 , Nov 5, 2011
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        William Koepp said: Friday, November 04, 2011 4:55 PM
        > Mr. Buckley there is no fail safe to
        > definition of your standards.

        Your original post said "Any help would be much appreciated."
        DAvid was giving you very sound advice. There is "a fail safe of
        his definition". Many systems use encoding on a beam to help
        detect the beam from being swamped by ambient.

        Do you know what a DC Blocking cap is? Rather than try to detect
        the presence or absense of light, (which shows up as a higher or
        lower DC level) most break-beams try to detect the presence or
        absense of an encoded frequency put ontop of the beam. Putting
        that signal on the beam is called Modulation. A photo cell that
        detects levels can be tricked by any additional source of light.
        However, if you put a DC blocking capacitor in line with the
        signal, no matter if there's a little steady ambient light, or a
        lot of steady ambient light, the output of the cap is 0V. DC
        does not pass through a cap. However, if the signal is modulated
        with a higher frequency, the signal appears at the output of the
        cap, because caps pass the AC component riding on a DC signal
        level, while blocking the DC from passing.

        So if you look for that frequency at the output, you know your
        transmitter is what is being seen, rather than some unmodulated
        source, like a laser pointer or flashlight. Yes someone can try
        to match your frequency, and maybe then get past the saftey
        curtain, but it won't be casually by accident.

        Do I know what I'm talking about? Yes. I've made a commercial
        laser break-beam that operates over 1/4 mile separation under
        all sort of harsh conditions. It is the beam of a laser for a
        barrel-racing timer. I put a high frequency on the beam, so high
        most sources like an IR remote control, cannot simulate it. Then
        I put a second secret modulation on it almost no one can see
        unless they know it is there. I used phase lock loops to recover
        both. I know when there's something in the beam, even when the
        eye is looking almost right into the sun. Turns out the first
        encoding was secure enough, so the second was not necessary in
        production.

        You might want to offer Mr. Buckley an appology for trying to
        tell you something important, which you had promised to be "much
        appreciaed", but instead was blown off.

        Here's a suggestion. Look at the IS471F. It is used often as a
        proximity detector. It modulates an external LED (which could be
        a laser) and looks for its own modulation on the reflection to
        know if something is in front of it a few inches. However, you
        could separate the detector and run wires to the transmitting
        LED, and so, look straight down the beam without bouncing it off
        anything, and get the range you need, and much greater if you
        used a concentrating lenses on both ends. I've done this with a
        visible laser and a similar part, the S6986, to retroreflective
        material, and had it work reliably over 3 meters separation.
        Remember that's out and back. It would go much further without
        having to reflect off of a material.

        Here's an article on making an IRPD.
        http://www.instructables.com/id/A-very-simple-proximity-detector
        /?ALLSTEPS

        Randy
      • William Koepp
        Mr. Buckley I do apologize for my mood. The way i came off was not intended, i am just stressed with this project. Mr Dumse a encoded signal was my original
        Message 3 of 25 , Nov 6, 2011
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          Mr. Buckley I do apologize for my mood. The way i came off was not intended, i am just stressed with this project. Mr Dumse a encoded signal was my original thought but unfortunately i am unable to do that at this point. I do greatly appreciate everyone that did comment and help. All of you guys are intelligent and experienced and that is why i come to y'all. I have decided to go with lasers and will just have to cut back somewhere else on the project, as things progress in the project i will update y'all if you like and any future comments i will be more welcoming of and less apprehensive.  
        • William
          To add on to the below statement, when i said unfortunately i am unable to do that at this point about encoding i was referring to that i am unable to use
          Message 4 of 25 , Nov 6, 2011
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            To add on to the below statement, when i said "unfortunately i am unable to do that at this point" about encoding i was referring to that i am unable to use anything like a microcontroller or PLC at the time. I am defiantly going to see if i can work in that idea some way of using the cap.

            --- In beam@yahoogroups.com, William Koepp <william.koepp@...> wrote:
            >
            > Mr. Buckley I do apologize for my mood. The way i came off was not intended, i am just stressed with this project. Mr Dumse a encoded signal was my original thought but unfortunately i am unable to do that at this point. I do greatly appreciate everyone that did comment and help. All of you guys are intelligent and experienced and that is why i come to y'all. I have decided to go with lasers and will just have to cut back somewhere else on the project, as things progress in the project i will update y'all if you like and any future comments i will be more welcoming of and less apprehensive.  
            >
          • David Buckley
            That is what projects do, they stress us! Nothing is ever perfect either but if we are aware of problem areas we can at least address them in manuals etc or
            Message 5 of 25 , Nov 6, 2011
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              That is what projects do, they stress us!
              Nothing is ever perfect either but if we are aware of problem areas we can at least address them in manuals etc or for a project explain that in real life such a problem would have to be addressed.
              I think if it was me I would use a tightly directed beam (shone down a tube) of 38KHz IR and use a 38KHz receiver (eg TSOP4838). Almost foolproof.
              Cheaper and better than using lasers. All you need is a 50c micro to generate the 38KHz (eg a PicAxe08 makes that very easy to do), an IR LED, resistor and a TSOP4838.
              DAvid
               
               
              ----- Original Message -----
              Sent: Monday, November 07, 2011 1:57 AM
              Subject: RE: [beam] Lasers

               

              Mr. Buckley I do apologize for my mood. The way i came off was not intended, i am just stressed with this project. Mr Dumse a encoded signal was my original thought but unfortunately i am unable to do that at this point. I do greatly appreciate everyone that did comment and help. All of you guys are intelligent and experienced and that is why i come to y'all. I have decided to go with lasers and will just have to cut back somewhere else on the project, as things progress in the project i will update y'all if you like and any future comments i will be more welcoming of and less apprehensive.  
              < /div>

            • David Buckley
              I think when you say unable to use anything like a microcontroller or PLC you are sort of mixing things up and making life difficult. A PLC generally is a
              Message 6 of 25 , Nov 6, 2011
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                I think when you say unable to use anything like a microcontroller or PLC  you are sort of  mixing things up and making life difficult.
                A PLC generally is a box of electronics and never cheap.
                A microcontroller on the other hand is just a chip and (if you choose the right one) is as cheap and as hard to use as an LED.
                Whereas one time you might have used a 555 timer (for example to generate a 38KHz signal) it is now easier to use a microcontroller chip.
                And since this is Beam, you should understand freeforming so you wouldn't even need a PCB.
                 
                 
                ----- Original Message -----
                From: William
                Sent: Monday, November 07, 2011 2:10 AM
                Subject: [beam] Re: Lasers

                 

                To add on to the below statement, when i said "unfortunately i am unable to do that at this point" about encoding i was referring to that i am unable to use anything like a microcontroller or PLC at the time. I am defiantly going to see if i can work in that idea some way of using the cap.

                --- In beam@yahoogroups.com, William Koepp <william.koepp@...> wrote:
                >
                > Mr. Buckley I do apologize for my mood. The way i came off was not intended, i am just stressed with this project. Mr Dumse a encoded signal was my original thought but unfortunately i am unable to do that at this point. I do greatly appreciate everyone that did comment and help. All of you guys are intelligent and experienced and that is why i come to y'all. I have decided to go with lasers and will just have to cut back somewhere else on the project, as things progress in the project i will update y'all if you like and any future comments i will be more welcoming of and less apprehensive.  
                >

              • William Koepp
                Yes i am unable to use micro s. For some reason my professor seems against them and is all big on PLC s, especially Siemens made ones. I am unable though to
                Message 7 of 25 , Nov 6, 2011
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                  Yes i am unable to use micro's. For some reason my professor seems against them and is all big on PLC's, especially Siemens made ones. I am unable though to use a PLC because we have none to spare and as you said they are costly. I am really going to try and push the topic of using microcontrollers for this do to the added safety it can provide. I have yet to work with any true PLCs myself, so in your experience would it be easy to wire a PLC to the picaxes if i am able to go with those? We will eventually add a PLC into the system. To the freeforming, well i am ok but far from great, we have some perf/proto board on hand i think so i might as well use it.  
                • David Buckley
                  Seems as if your professor is living in the last century or at least fondly imagining that he is teaching you the way industry does it, Buy some equipment,
                  Message 8 of 25 , Nov 6, 2011
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                    Seems as if your professor is living in the last century or at least fondly imagining that he is teaching you the way 'industry' does it, Buy some equipment, wire it together and hey presto you have your system. In that case instead of designing a light curtain he should be insisting you obtain items off the shelf to create your curtain.
                     
                    Why would you wan to wire a PLC to a PicAxe? See later.
                     
                    I suggested you generate a 38KHz signal to drive an IR-LED, you can't (or at least you couldn't) do that with a PLC. In the past you would have used a 555 timer IC or similar to generate the signal which would of course depend on the stability of the resistors and capacitors used.
                    Nowadays it is easier to use a singlechip microcontroller with an inbuilt oscillator and program a pin to output a 38KHz signal.
                    I mentioned a PicAxe because they are easy to program and generating 38KHz output and signals to Sony codes is built into the language and they don't need a programmer because they have a bootloader. You could do the same with other small PICs or AVRs but maybe need to get programmers and compilers. Reinventing wheels is costly in terms of time at least. And if you are making a one-off who cares if the parts cost is 10c or 50c. Having generated your 38KHz IR beam a 38KHz detector IC would do all the work giving you a low for signal present and high for no signal. You could feed that signal into whatever latching circuit you want to use. It would be the output from that circuit you would feed to the PLC. Now the latch maybe another small microcontroller that is looking for codes in the IR stream for added safety. Again the PicAxe chips have that functionality (for Sony codes) built into the language.
                    It depends on the PLC you use what logic levels it can read.
                    You need to understand PLCs because that is what industry uses, they are very rugged and virtually bomb proof but it is horses for courses, you wouldn't try and clean your teeth with a yard brush.
                    DAvid
                     
                     
                    ----- Original Message -----
                    Sent: Monday, November 07, 2011 3:59 AM
                    Subject: Re: [beam] Re: Lasers

                     

                    Yes i am unable to use micro's. For some reason my professor seems against them and is all big on PLC's, especially Siemens made ones. I am unable though to use a PLC because we have none to spare and as you said they are costly. I am really going to try and push the topic of using microcontrollers for this do to the added safety it can provide. I have yet to work with any true PLCs myself, so in your experience would it be easy to wire a PLC to the picaxes if i am able to go with those? We will eventually add a PLC into the system. To the freeforming, well i am ok but far from great, we have some perf/proto board on hand i think so i might as well use it.  

                  • William Koepp
                    Hahaha yeah he does do the when i was in the industry... alot. The reason i asked is because he wants to get rid of the adept controller it has and wire it
                    Message 9 of 25 , Nov 6, 2011
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                      Hahaha yeah he does do the "when i was in the industry..." alot. The reason i asked is because he wants to get rid of the adept controller it has and wire it to a PLC sometime next year, which i dont understand because we are about to put a brand new $4k DEPS board into the controller. I just try to do as he asks and keep a good GPA. I will be taking a PLC course but it is not for another two semesters i believe.
                    • Randy M. Dumse
                      William said: Sunday, November 06, 2011 8:10 PM ... Maybe I m too long winded in my replies. Seems you ve missed my point. Let me make it simple. Get an IS471F
                      Message 10 of 25 , Nov 7, 2011
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                        William said: Sunday, November 06, 2011 8:10 PM
                        > When i said "unfortunately i am unable to do that
                        > at this point" about encoding i was referring to
                        > that i am unable to use anything like a
                        > microcontroller or PLC at the time. ...
                        > I am defiantly going to see if i can work
                        > in that idea some way of using the cap.

                        Maybe I'm too long winded in my replies. Seems you've missed my
                        point.

                        Let me make it simple.

                        Get an IS471F and a matching IR LED. Put the IS471F on one side
                        of the opening. Put the IR LED (via wires run on the floor or
                        elsewise) on the other side.

                        You can get ~9" detection doing this as an IRPD, but straight
                        on, as a break-beam it might go quite a bit further. Then you
                        have your encoding, already built in. The IS471F provides the
                        drive to the LED, and that drive is encoded. Then inside the
                        IS471F is the whole circuit that checks incoming IR light for
                        that encoding. Very simple. Very cheap.

                        http://www.junun.org/MarkIII/Info.jsp?item=46 $2.50
                        http://www.junun.org/MarkIII/Info.jsp?item=47 $2.50

                        If you don't get the range you want (testing is called "an
                        experiment", useful in your learning) you can extend it by
                        putting the LED and the detector at the focal point of a lens.
                        Probably cheaper, you could use a laser for the IR LED. Or use
                        the similar S6986, and use a visible laser. Only a little more
                        expensive, but is much easier to get lined up.

                        http://www.junun.org/MarkIII/Info.jsp?item=79 $4.00
                        http://www.dealextreme.com/p/6mm-5mw-red-laser-module-3-5-4-5v-1
                        3378 $1.60

                        There's your whole project. Output is a open collector to GND to
                        signal something in the beam.

                        Randy
                      • William Koepp
                        Thank you Randy for the idea. I am going to try to use a Picaxe or 555 timer though. we have the 555 s on hand. Yes i think your reply hand gone a bit over my
                        Message 11 of 25 , Nov 7, 2011
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                          Thank you Randy for the idea. I am going to try to use a Picaxe or 555 timer though. we have the 555's on hand. Yes i think your reply hand gone a bit over my head, and if i tried to explain it to the others, who have even less understanding of electronics, it would def go right over there head. I will keep your idea's in mind though because situations are constantly changing. I have my proposal in about 30mins, so i will find out what is excepted and what is not.

                        • Alvaro Barcellos
                          If you put a DC blocking capacitor in line with the signal, no matter if there s a little steady ambient light, or a lot of steady ambient light, the output
                          Message 12 of 25 , Nov 7, 2011
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                            " If you put a DC blocking capacitor in line with the
                            signal, no matter if there's a little steady ambient light, or a
                            lot of steady ambient light, the output of the cap is 0V. DC
                            does not pass through a cap. However, if the signal is modulated
                            with a higher frequency, the signal appears at the output of the
                            cap, because caps pass the AC component riding on a DC signal
                            level, while blocking the DC from passing. "

                            A basic lesson.

                            use simply solutions, a capacitor, a crystal (32.768 kHz) or ressonator (445kHz) and a watch-dog.


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