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27932[SeattleRobotics] Re: Sensing Lasers..

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  • PeterBalch
    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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