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Sensing Lasers..

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  • Mustafa
    Hi everyone.. I am making a circuit for sensing laser modulated at a frequency of 10kHz. I tried using phototransistors and photodiodes to sense the laser, but
    Message 1 of 12 , Jun 1, 2006
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      Hi everyone..

      I am making a circuit for sensing laser modulated at a frequency of
      10kHz. I tried using phototransistors and photodiodes to sense the
      laser, but both are unable to give sufficient response for laser. the
      photodiode circuit works fine with ired, but does not show any change
      in output with laser.. Does anyone know what can be used to solve the
      problem? The laser used is a small ordinary one available from
      road-side vendors.


      ---------------------------------
      My code never has bugs. It just develops random features...
      Mustafa
      Electronics Engineering, SVNIT





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    • Triffid Hunter
      see if a normal red led is fast enough.
      Message 2 of 12 , Jun 1, 2006
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        see if a normal red led is fast enough.

        Mustafa wrote:
        > Hi everyone..
        >
        > I am making a circuit for sensing laser modulated at a frequency of
        > 10kHz. I tried using phototransistors and photodiodes to sense the
        > laser, but both are unable to give sufficient response for laser. the
        > photodiode circuit works fine with ired, but does not show any change
        > in output with laser.. Does anyone know what can be used to solve the
        > problem? The laser used is a small ordinary one available from
        > road-side vendors.
        >
        >
        > ---------------------------------
        > My code never has bugs. It just develops random features...
        > Mustafa
        > Electronics Engineering, SVNIT
        >
        >
        >
        >
        >
        > __________________________________________________
        > Do You Yahoo!?
        > Tired of spam? Yahoo! Mail has the best spam protection around
        > http://mail.yahoo.com
        >
        >
        > Visit the SRS Website at http://www.seattlerobotics.org
        > Yahoo! Groups Links
        >
        >
        >
        >
        >
        >
        >
      • Alan King
        ... Look at the beam angle and sensitivity. Lasers put out very little light except down the beam, unless your spot is right on the detector you won t see
        Message 3 of 12 , Jun 1, 2006
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          Mustafa wrote:

          >Hi everyone..
          >
          >I am making a circuit for sensing laser modulated at a frequency of
          >10kHz. I tried using phototransistors and photodiodes to sense the
          >laser, but both are unable to give sufficient response for laser. the
          >photodiode circuit works fine with ired, but does not show any change
          >in output with laser.. Does anyone know what can be used to solve the
          >problem? The laser used is a small ordinary one available from
          >road-side vendors.
          >
          >
          >


          Look at the beam angle and sensitivity. Lasers put out very little
          light except down the beam, unless your spot is right on the detector
          you won't see much of anything. Get one that has changable lenses and
          spread it out, or if you need long distances get the spot on the
          detector. If you've already got the spot on the detector, you may be
          just swamping out the detector, with so much light coming in it may just
          not be turning off at all. If it's working with the relatively low
          amount from an IR LED it may be way too sensitive for a direct laser
          beam.. Also, working with IR LED? Cheap red laser pointer? If it has
          a dark IR filter you may not be getting much of anything to the sensor
          at all if you're using the same sensor. Of course if you've tried
          several then most likely at least one or two were clear enough.

          Alan
        • :: [-] HaAzIq [-] ::
          hye all .. can someone help me 2 compile the program in this site .. http://www.seattlerobotics.org/encoder/200010/robarnold.html ... Try the all-new Yahoo!
          Message 4 of 12 , Jun 1, 2006
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            hye all ..

            can someone help me 2 compile the program in this site ..

            http://www.seattlerobotics.org/encoder/200010/robarnold.html


            ---------------------------------
            Try the all-new Yahoo! Mail . "The New Version is radically easier to use" – The Wall Street Journal

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          • Randy M. Dumse
            ... Your laser probably isn t actually outputing a modulated signal. The constant current circuit in later lasers have large caps. They can t be externally
            Message 5 of 12 , Jun 1, 2006
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              > The laser used is a small ordinary one available from
              > road-side vendors.

              Your laser probably isn't actually outputing a modulated signal.

              The constant current circuit in later lasers have large caps.
              They can't be externally modulated at any signficant frequency.
              The earlier ones could be modulated at up to 500KHz before
              output started to roll off. We had to special order our laser
              modules with the simpler constant current circuit to have useful
              modulation.

              Randy
              www.newmicros.com
            • PeterBalch
              ... What kind of phototransistors and photodiodes were you using? IR phototransistors will work reasonably well with visible light so long as you get the ones
              Message 6 of 12 , Jun 1, 2006
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                > I am making a circuit for sensing laser modulated at a frequency of
                > 10kHz. I tried using phototransistors and photodiodes to sense the
                > laser, but both are unable to give sufficient response for laser. the
                > photodiode circuit works fine with ired,

                What kind of phototransistors and photodiodes were you using? IR
                phototransistors will work reasonably well with visible light so long as
                you get the ones with clear plastic. The dark-plastic ones have IR filters.
                10kHz is no problem of course; rise and fall times are a few uS or less.

                What sort of a laser are you using? A laser-pointer? I just tried one on a
                clear-plastic IR phototransistor and it worked fine. My LED wasn't
                modulated though. Is your problem with the modulation?

                > see if a normal red led is fast enough.

                Do you mean as a light-source to test the phototransistor?

                Or do you mean as a light sensor? (Yes, LEDs will work as light sensors. I
                didn't believe it until I tried it. Weird!) I've not seen any figures for
                their spectrum or frequency response. Do you have any?

                Peter
              • Jim McBride
                That is how my beam robot heads to the light!! Two Flashing LED eyes ... JIMc x22661 National Ignition Facility [Non-text portions of this message have been
                Message 7 of 12 , Jun 1, 2006
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                  That is how my beam robot heads to the light!! Two Flashing LED "eyes"

                  At 11:42 AM 6/1/2006, you wrote:
                  >Or do you mean as a light sensor? (Yes, LEDs will work as light sensors. I
                  >didn't believe it until I tried it. Weird!) I've not seen any figures for
                  >their spectrum or frequency response. Do you have any?

                  JIMc
                  x22661
                  National
                  Ignition
                  Facility



                  [Non-text portions of this message have been removed]
                • Mustafa
                  Thanks alan, but i had already changed the lens to spread out the laser. The phototransistor and photodiode i used are clear plastic types and so i do not
                  Message 8 of 12 , Jun 2, 2006
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                    Thanks alan, but i had already changed the lens to spread out the
                    laser. The phototransistor and photodiode i used are clear plastic
                    types and so i do not expect them to have an ir filter.

                    Also i am having different problems while using phototransistor and
                    photodiode. The phototransistor is able to sense unmodulated laser
                    quite well, however when i observed the output from the
                    phototransistor (for this the output was observed directly from the
                    collector terminal, i.e. before any bandpass filter stage) with
                    modulated laser on a CRO, i found narrow and small amplitude (around
                    1.2V) spikes at the same 10 KHz frequency instead of a square wave
                    with 5V amplitude.

                    On the other hand the photodiode shows very little response towards
                    laser (unmodulated) and that too when the laser is extremely close to
                    the diode.

                    The application actually requires sensing the laser from about 1 m and
                    that is the reason behind using a laser instead of ir led.

                    Btw Jim could you please give more information on how leds can be used
                    as light sensors.. do they offer any advantage over photodiodes that
                    are supposed to do the job?



                    --- In SeattleRobotics@yahoogroups.com, Alan King <alan@...> wrote:
                    >
                    > Mustafa wrote:
                    >
                    > >Hi everyone..
                    > >
                    > >I am making a circuit for sensing laser modulated at a frequency of
                    > >10kHz. I tried using phototransistors and photodiodes to sense the
                    > >laser, but both are unable to give sufficient response for laser. the
                    > >photodiode circuit works fine with ired, but does not show any change
                    > >in output with laser.. Does anyone know what can be used to solve the
                    > >problem? The laser used is a small ordinary one available from
                    > >road-side vendors.
                    > >
                    > >
                    > >
                    >
                    >
                    > Look at the beam angle and sensitivity. Lasers put out very little
                    > light except down the beam, unless your spot is right on the detector
                    > you won't see much of anything. Get one that has changable lenses and
                    > spread it out, or if you need long distances get the spot on the
                    > detector. If you've already got the spot on the detector, you may be
                    > just swamping out the detector, with so much light coming in it may
                    just
                    > not be turning off at all. If it's working with the relatively low
                    > amount from an IR LED it may be way too sensitive for a direct laser
                    > beam.. Also, working with IR LED? Cheap red laser pointer? If it has
                    > a dark IR filter you may not be getting much of anything to the sensor
                    > at all if you're using the same sensor. Of course if you've tried
                    > several then most likely at least one or two were clear enough.
                    >
                    > Alan
                    >
                  • Jim McBride
                    I am not sure if there are any advantages other than their size. Take your volt meter and connect it to the leads of an LED. You will find that it gives off
                    Message 9 of 12 , Jun 2, 2006
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                      I am not sure if there are any advantages other than their size. Take your
                      volt meter and connect it to the leads of an LED. You will find that it
                      gives off voltage proportional to the amount of light that you shine on it.
                      Beam robots use flashing LEDs. The LEDs will flash at a certain threshold
                      voltage. As the cap on the robot slowly builds up voltage the LEDs get
                      closer to that threshold voltage. The voltage that is generated due to
                      light is added to the caps voltage. In this way when the cap has a
                      sufficient charge, the LED with the most light on it will hit that
                      threshold voltage first which triggers it. The "neuron" engine is tripped
                      by the trigger and the caps power is dumped to the opposite motor, spinning
                      it. This will make the robot turn in the direction of the light.
                      Are you trying to see the direct light of the laser?

                      At 07:37 AM 6/2/2006, you wrote:
                      >Thanks alan, but i had already changed the lens to spread out the
                      >laser. The phototransistor and photodiode i used are clear plastic
                      >types and so i do not expect them to have an ir filter.
                      >
                      >Also i am having different problems while using phototransistor and
                      >photodiode. The phototransistor is able to sense unmodulated laser
                      >quite well, however when i observed the output from the
                      >phototransistor (for this the output was observed directly from the
                      >collector terminal, i.e. before any bandpass filter stage) with
                      >modulated laser on a CRO, i found narrow and small amplitude (around
                      >1.2V) spikes at the same 10 KHz frequency instead of a square wave
                      >with 5V amplitude.
                      >
                      >On the other hand the photodiode shows very little response towards
                      >laser (unmodulated) and that too when the laser is extremely close to
                      >the diode.
                      >
                      >The application actually requires sensing the laser from about 1 m and
                      >that is the reason behind using a laser instead of ir led.
                      >
                      >Btw Jim could you please give more information on how leds can be used
                      >as light sensors.. do they offer any advantage over photodiodes that
                      >are supposed to do the job?
                      >
                      >
                      >
                      >--- In SeattleRobotics@yahoogroups.com, Alan King <alan@...> wrote:
                      > >
                      > > Mustafa wrote:
                      > >
                      > > >Hi everyone..
                      > > >
                      > > >I am making a circuit for sensing laser modulated at a frequency of
                      > > >10kHz. I tried using phototransistors and photodiodes to sense the
                      > > >laser, but both are unable to give sufficient response for laser. the
                      > > >photodiode circuit works fine with ired, but does not show any change
                      > > >in output with laser.. Does anyone know what can be used to solve the
                      > > >problem? The laser used is a small ordinary one available from
                      > > >road-side vendors.
                      > > >
                      > > >
                      > > >
                      > >
                      > >
                      > > Look at the beam angle and sensitivity. Lasers put out very little
                      > > light except down the beam, unless your spot is right on the detector
                      > > you won't see much of anything. Get one that has changable lenses and
                      > > spread it out, or if you need long distances get the spot on the
                      > > detector. If you've already got the spot on the detector, you may be
                      > > just swamping out the detector, with so much light coming in it may
                      >just
                      > > not be turning off at all. If it's working with the relatively low
                      > > amount from an IR LED it may be way too sensitive for a direct laser
                      > > beam.. Also, working with IR LED? Cheap red laser pointer? If it has
                      > > a dark IR filter you may not be getting much of anything to the sensor
                      > > at all if you're using the same sensor. Of course if you've tried
                      > > several then most likely at least one or two were clear enough.
                      > >
                      > > Alan
                      > >
                      >
                      >
                      >
                      >
                      >
                      >
                      >
                      >Visit the SRS Website at http://www.seattlerobotics.org
                      >Yahoo! Groups Links
                      >
                      >
                      >
                      >

                      JIMc
                      x22661
                      National
                      Ignition
                      Facility



                      [Non-text portions of this message have been removed]
                    • Pedro Drummond
                      ... I m not sure I understand this, but do you mean 1m is too much for IR? I have seen homemade IR links (lens-less) up to 10m, and up to 20m using lenses. Our
                      Message 10 of 12 , Jun 2, 2006
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                        >The application actually requires sensing the laser from about 1 m and that
                        >is the reason behind using a laser instead of ir led.

                        I'm not sure I understand this, but do you mean 1m is too much for IR? I
                        have seen homemade IR links (lens-less) up to 10m, and up to 20m using
                        lenses. Our TV remote has a better range than 1m.






                        --- In SeattleRobotics@yahoogroups.com, Alan King <alan@...> wrote:
                        >
                        > Mustafa wrote:
                        >
                        > >Hi everyone..
                        > >
                        > >I am making a circuit for sensing laser modulated at a frequency of
                        > >10kHz. I tried using phototransistors and photodiodes to sense the
                        > >laser, but both are unable to give sufficient response for laser. the
                        > >photodiode circuit works fine with ired, but does not show any change
                        > >in output with laser.. Does anyone know what can be used to solve the
                        > >problem? The laser used is a small ordinary one available from
                        > >road-side vendors.
                        > >
                        > >
                        > >
                        >
                        >
                        > Look at the beam angle and sensitivity. Lasers put out very little
                        > light except down the beam, unless your spot is right on the detector
                        > you won't see much of anything. Get one that has changable lenses and
                        > spread it out, or if you need long distances get the spot on the
                        > detector. If you've already got the spot on the detector, you may be
                        > just swamping out the detector, with so much light coming in it may
                        just
                        > not be turning off at all. If it's working with the relatively low
                        > amount from an IR LED it may be way too sensitive for a direct laser
                        > beam.. Also, working with IR LED? Cheap red laser pointer? If it
                        > has a dark IR filter you may not be getting much of anything to the
                        > sensor at all if you're using the same sensor. Of course if you've
                        > tried several then most likely at least one or two were clear enough.
                        >
                        > Alan
                        >







                        Visit the SRS Website at http://www.seattlerobotics.org Yahoo! Groups Links
                      • Mustafa
                        Sorry to confuse you Pedro. But this is only a prototype of an application working on lasers. ... m and that ... IR? I ... using ... frequency of ... the ...
                        Message 11 of 12 , Jun 3, 2006
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                          Sorry to confuse you Pedro. But this is only a prototype of an
                          application working on lasers.


                          --- In SeattleRobotics@yahoogroups.com, "Pedro Drummond"
                          <electronics@...> wrote:
                          >
                          >
                          > >The application actually requires sensing the laser from about 1
                          m and that
                          > >is the reason behind using a laser instead of ir led.
                          >
                          > I'm not sure I understand this, but do you mean 1m is too much for
                          IR? I
                          > have seen homemade IR links (lens-less) up to 10m, and up to 20m
                          using
                          > lenses. Our TV remote has a better range than 1m.
                          >
                          >
                          >
                          >
                          >
                          > --- In SeattleRobotics@yahoogroups.com, Alan King <alan@> wrote:
                          > >
                          > > Mustafa wrote:
                          > >
                          > > >Hi everyone..
                          > > >
                          > > >I am making a circuit for sensing laser modulated at a
                          frequency of
                          > > >10kHz. I tried using phototransistors and photodiodes to sense
                          the
                          > > >laser, but both are unable to give sufficient response for
                          laser. the
                          > > >photodiode circuit works fine with ired, but does not show any
                          change
                          > > >in output with laser.. Does anyone know what can be used to
                          solve the
                          > > >problem? The laser used is a small ordinary one available from
                          > > >road-side vendors.
                          > > >
                          > > >
                          > > >
                          > >
                          > >
                          > > Look at the beam angle and sensitivity. Lasers put out very
                          little
                          > > light except down the beam, unless your spot is right on the
                          detector
                          > > you won't see much of anything. Get one that has changable
                          lenses and
                          > > spread it out, or if you need long distances get the spot on the
                          > > detector. If you've already got the spot on the detector, you
                          may be
                          > > just swamping out the detector, with so much light coming in it
                          may
                          > just
                          > > not be turning off at all. If it's working with the relatively
                          low
                          > > amount from an IR LED it may be way too sensitive for a direct
                          laser
                          > > beam.. Also, working with IR LED? Cheap red laser pointer? If
                          it
                          > > has a dark IR filter you may not be getting much of anything to
                          the
                          > > sensor at all if you're using the same sensor. Of course if
                          you've
                          > > tried several then most likely at least one or two were clear
                          enough.
                          > >
                          > > Alan
                          > >
                          >
                          >
                          >
                          >
                          >
                          >
                          >
                          > Visit the SRS Website at http://www.seattlerobotics.org Yahoo!
                          Groups Links
                          >
                        • PeterBalch
                          ... Sounds like a laser modulation to me. How well did the phottransistor respond to a TV remote control? ... I don t understand that. When I tried it
                          Message 12 of 12 , Jun 3, 2006
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                            > when i observed the output from the
                            > phototransistor ... on a CRO, i found narrow and small amplitude (around
                            > 1.2V) spikes at the same 10 KHz frequency instead of a square wave
                            > with 5V amplitude.

                            Sounds like a laser modulation to me.

                            How well did the phottransistor respond to a TV remote control?

                            > On the other hand the photodiode shows very little response towards
                            > laser (unmodulated) and that too when the laser is extremely close to
                            > the diode.

                            I don't understand that. When I tried it yesterday, there way a huge
                            response even if I fired the laser from the other side of the room. I wan't
                            using a beam-spreader. Is that the problem? Has it spread the beam too
                            much? Is there a lot of ambient illumination?

                            > The application actually requires sensing the laser from about 1 m and
                            > that is the reason behind using a laser instead of ir led.

                            A TV remote control will work over a much longer distance.

                            Why not use one of the IR sensors that has an amp and demodulator built in?
                            It's only worthwhile building your own IR receiver if you're going to
                            produce a few thousand of them.

                            > how leds can be used
                            > as light sensors.. do they offer any advantage over photodiodes that
                            > are supposed to do the job?

                            They're very much cheaper but they're nowhere near as good. I've filed the
                            "LEDs work as sensors" idea in the interesting-but-useless category.

                            Peter
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