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help with passive and active IR

Discussion in 'Electronic Basics' started by Joe, Sep 13, 2003.

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  1. Joe

    Joe Guest

    Awhile back, I built a passive IR system to take pictures. I built it by the
    plans on in his section on homebrew trail

    When I use it in a small area, with a solid backdrop it works OK, but if I
    try to 'watch' a trail, I am getting a lot of false triggers. Presumably
    from air currents, and possibly leaves, grass, and tree limbs moving side
    to side in the wind.

    I was thinking of using the passive system to turn on another, active
    system. I have a laser pointer that I took apart and could modulate, but I
    would rather have the light be invisible. The passive system I use now turns
    on a relay which trips the camera shutter. I would like it to turn on
    another IR LED which would shoot a beam into the target area and if the beam
    gets reflected (by something which has moved into the target area), I could
    trip the shutter and take the picture.

    The problem is, I am not sure how to detect the reflection of the IR beam
    (or laser). This is a battery powered device, so I wouldn't want the active
    portion of the detector 'on' all the time. I would also like to be able to
    use this day or night. Any help is appreciated.

  2. I'll be darned if I could find any reference to home-brew trail
    cameras on this page. Can you give a better url?
    Before you discard what you have and start over, it might be possible
    to improve what you have. But I can't find it to discuss that.
  3. Joe

    Joe Guest

    Hi John,
    My apologies, he has changed his page drastically since the last time I
    visited it. Here is a url direct to the PIR page.

    I was not planning on discarding the system I have. I just thought that
    adding an active sensor to it may decrease the number of false triggers.

  4. Guest

    Guest Guest

    Hi Joe

    The field of view for the IR sensor is about 110 degrees.
    If you limit the field of view by putting some black tubing on the front
    of the sensor it might reduce the false triggering.

    Colin G

    ----== Posted via Usenet.Com - Unlimited-Uncensored-Secure Usenet News==---- The #1 Newsgroup Service in the World! >100,000 Newsgroups
  5. Colubris

    Colubris Guest

    Hi Joe,
    If you check out the forums and other cam-related pages at that site,
    you'll find tons of info about the "falsing" problem and how to reduce
    it to reasonable levels.
    I've built the Passive/Active system as you describe, and while it's
    not difficult, I just about never use it in favor of the regular
    passive systems.
    BTW - the active sensor in this application does not detect a
    reflection from the target, but creates a "beam" which the target
    breaks by walking through it.
    Sometimes called "break-beam" detectors.

  6. Joe

    Joe Guest

    Thanks for the info Colin. I have been using tape to reduce the field of
    view. I was thinking I would be needing something to 'confirm' that
    something was actually in front of the sensor before wasting a photo, hence
    the 'dual system' idea. I was surprised by all the new stuff on jesses
    site, so I am going to go back and check it out. Maybe he already has
    something there.
    Thanks again for the info.


  7. Joe

    Joe Guest

    Hi Arch,

    thanks for the info. I was surprised by some of the new stuff that's out
    there now so I will be checking closer to see how to minimize false

    On the subject of break beam detectors. I thought that to build one you
    needed a 'transmitter' at point A and the receiver at point B. After
    properly aligning them (ugh!) then when a target breaks the beam, you can
    energize a relay, or turn on a transistor. I wanted to stay away from such a
    system and try to have the transmitter and receiver in the same box, aimed
    at the center of the field of view. Then when the PIR detects something,
    turn on the active transmitter for 5 or 10 seconds (to give the target time
    to get into the center of the field of view), and when the receiver detects
    the reflection, it triggers the camera shutter. I was thinking of (of all
    things), how a laser guided munition finds its target. It homes in on the
    reflected laser beam that is directed at the target either by the launch
    aircraft or by troops on the ground. The target is 'painted' and the
    munition just homes in on the reflection. I guess active radar guided
    munitions work the same way.

    Maybe something like that would be more grief then it is worth. I thought it
    would be fun to build and see how it worked anyway.

    Thank you again for the info,

  8. Colubris

    Colubris Guest

    Hi Arch,
    Hi Joe,
    The break-beam detectors work just as you described. You can also use
    a reflector at "point B" instead of a receiver. The mirror reflects
    the "beam" back at the transmitter unit - which also has the receiver
    in it. That way all the electronics are in one case. Sometimes called
    a "retro-reflective break-beam detector". The alignment is still a
    pain - which is one of the main reasons I don't use the setup anymore.
    You also tend to miss a lot, because the active is so precise.

    I don't think you could expect to get an active IR signal to reliably
    reflect off of a passing animal at a reasonable range with an
    affordable home-brewed circuit. Maybe one of the pro's here can come
    up with an idea for that.

    There's also the possibility of using a microwave or ultrasonic
    detector that gets activated by the passive. Achieve the same results
    without the drawbacks of the active IR setup.

  9. Joe

    Joe Guest

    Hi Arch,

    I didn't think about a reflector for the break beam. Still a pain to align
    tho. If IR is not good, what about laser? I have a laser pointer I took
    apart and I can pulse it. The problem is that it would be visible, but
    possibly more reliable then active IR? I don't really need a 60 ft range for
    the PIR . What I do for my regular business is evict or sometimes trap and
    remove nuisance wild animals from peoples attics, sheds, crawlspaces, etc. I
    use the trailcam setup so I can show a picture to the client of whatever is
    causing them the grief if they don't already know what animal it is. It also
    comes in handy doing evictions where I have proof that the animal is gone
    (by the lack of activity) once I do what I have to in order to make them
    move. The ranges I am working at are usually under 30 feet. Most times, the
    trailcam is within 20 feet of the den.

    I don't know if I want to play around with microwave (I guess that would be
    a radar of sorts), but ultrasonic may be ok. I'll do a google search on it
    and see what I can find.

    Thanks again,
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