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[Fwd: Re: [SeattleRobotics] A very strange IR sensor problem..]

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  • John Beatty
    ... Subject: Re: [SeattleRobotics] A very strange IR sensor problem.. Date: Sat, 2 Nov 2002 13:57:37 -0500 From: drait Another
    Message 1 of 1 , Nov 2, 2002
      -------- Original Message --------
      Subject: Re: [SeattleRobotics] A very strange IR sensor problem..
      Date: Sat, 2 Nov 2002 13:57:37 -0500
      From: "drait" <drait@...>

      Another interesting oddity while using a DS1621 Temp sensor.
      If I bring my fluorescent desk lamp close (less than 12 inches) for
      a short time it just quits functioning. If I remove the lamp it will
      resume in 1.5-2.0 minutes. This device is in a ceramic pack.
      Go figure ! DRAIT

      ----- Original Message -----
      From: "John Beatty" <john.beatty@...>
      To: "SeattleRobotics" <SeattleRobotics@yahoogroups.com>
      Sent: Saturday, November 02, 2002 12:34
      Subject: Re: [SeattleRobotics] A very strange IR sensor problem..

      > I once had a problem with an old fashioned boat echo sounder that
      > displayed the depth with a rotating arm at the end of which was a neon
      > lamp that flashed when the echo was received. The curious thing that I
      > noticed was that, at night, especially when the battery got a bit low,
      > the neon flashed much more brightly if you shone a torch on it. I deduce
      > that this was an exhibition of the photo-electric effect; and I wonder
      > if photo-diodes are any similar in this respect - their sensitivity
      > being enhanced by a low level of ambient lighting.
      > John Beatty
      > lmlingle wrote:
      > > I have a simple modulated IR sensor system setup on my bot.. It's
      > > digital and I know nothing is perfect so I expected some interference
      > > from ambient lighting. I planned for it, sheilded pretty well and had
      > > intended to poll it a number of times and then average to eliminate
      > > false "hits".. I thought this would be no problem.
      > >
      > > It is a problem however, because what's actually happening is the
      > > 38Khz infrared is combining with the ambient light to make my sensors
      > > super sensitive in well lit areas and not so in darkened areas. I know
      > > this is the case because killing the IR kills the sensor output.
      > >
      > > These aren't "false" hits from lucky desk lamps (I actually wish they
      > > were, because those I could deal with) These are legit, modulated IR
      > > from my emitters that's somehow enhansed in bright areas. Sure, you
      > > can cut the output to compensate, but then it runs blind in the
      > > shadows.
      > >
      > > It's so powerful the floor will set it off in a bright area, I can set
      > > it off from 3' away in a bright area and only 6" in a slightly less
      > > well lit area. Kill the IR though.. and boom, no more hits from any
      > > distance or light source. Totally impervious.
      > >
      > > Any insight you may have here, no matter how small will definately be
      > > news to me and would surely be appreciated.
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