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Infrared detectors

Discussion in 'Electronic Design' started by mkr5000, Apr 2, 2013.

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  1. mkr5000

    mkr5000 Guest

    How can these vary as far as "angle of detection"? Can they be very directional and some parts be very broad (180 degrees even?) or does it all depend on the type of lens you might use?

    I want to build a simple wireless heat detector for a stove and may not be able to point it "directly" at the stove. (I can get close though).

  2. Charlie E.

    Charlie E. Guest

    You will need to look at the datasheets for each individual part.
    Their angle of view can vary wildly depending on the materials and
    construction. Any 'optics' such as lense or sheilds will also have an
    effect. Remember, the wider the field of view, the less 'signal' from
    our stove you are going to received, so you want it wide enough to get
    your target, but not any wider!
  3. mkr5000

    mkr5000 Guest

    Wonder if I can use one of these cheap PIR motion modules and adjust the sensitivity so it's NOT very sensitive?

    I'm trying to detect heat from a wood stove about 3 feet away and using something that senses ambient room air temperature won't cut it -- need something that reacts the minute the stove is burning well -- thought maybe IR could do it?

    And no, don't want to mount a thermal switch ON the stove.
  4. Guest

    something like this?

    comes in different versions with different field of view, from the
    comments it looks
    like it is the 10degree version

  5. mkr5000

    mkr5000 Guest

    I saw that on sparkfun just this morning. Actually, don't need it to react "immediately" after a fire just when the stove starts radiating good heat from the surface (usually 1/2hr to an hour. And when it cools down, opens the circuit.

    Want it wireless because I'm a neatnic -- don't want a wire dangling from my stove and have a nice 120v outlet on the floor right beneath it (hence, bud box and a sensor right there on the outlet).

    It would also be hidden pretty much from movement of people in the room.
  6. Jasen Betts

    Jasen Betts Guest

    they detect rapid temperature changes. probably unsuitable.
    maybe a black thermistor and a headlight reflector to focus the heat?

    hoe long does it take the stove ti get hot after it's burning well
    can you put a sensor on (or in) the flue?

  7. Harbor freight, $20 infra red thermometer. laser pointed.

    Fresnel lens, quite accurate. Best 'thermometer' value in my entire
    collection. I have more accurate contact type transducers, but this one
    does the job, and I carried it in my pocket for a coupe years too.
    Still works fine.
  8. mkr5000

    mkr5000 Guest

    maybe I'll get one and take the guts out. never owned one of those and wonder how "directional" an IR sensor can be? I mean, I understand the laser being able to point but an IR detector? I suppose you just make sure there are no other IR sources close to it (how close?)

    Sure, if you point it toward a ceiling vent with nothing nearby but?
  9. miso

    miso Guest

    Well yes, but he probably meant the sensor in the PIR motion detector.
    They use a thin film type sensor. The sensor is also microphonic.
  10. mike

    mike Guest

    There are a zillion cheap wired or wireless motion-activated devices.
    Pick one that has the output you want.
    Remove the fresnel lens.
    Stick it behind a small computer fan to act as a shutter.
    May have to cut some of the blades off. Run the fan as slow
    as practical.
    Stick a pipe on the front end to restrict the field of view.
    Point it at the stove.
    Depending on the filtering in the device, the fan speed
    may make a simple sensitivity adjustment. Or maybe
    adjust the size of the hole in the end of the pipe.
  11. mkr5000

    mkr5000 Guest

    what a great idea -- that's what I'll do -- fun project to play with, will have to come up with a cool reflector. small metal funnel maybe?
  12. mkr5000

    mkr5000 Guest

    just bought a couple. been getting a lot of stuff from china and that's another post I've been meaning to do.

    how in the world they provide some of those complete modules at such a cost is beyond me. (and using parts from TI, etc). many of these I've computed parts cost alone (even in qty) -- and it's impossible there would be a profit. ?
  13. John S

    John S Guest

    Where can they be purchased, Jim?
  14. I'm unclear on how that works -- what if the plane never crosses in
    front of the sun?

    Re: stove heat detection, I've seen people mount old Ge transistors at
    the focus of a flashlight reflector. It might make a pretty sensitive
    detector if you created a diffamp with one in the reflector and the
    other behind it, facing the other direction. Not tried personally...

    -- john
  15. Bill Sloman

    Bill Sloman Guest

    The propellors are curved, reflective and twisted. You will probably
    get flashes of reflected sunlight modulated at the a frequency that is
    the number of blades multiplied by the rotation frequency, though
    Jim's scheme might not work on a heavily overcast day. Then again, it
    might be difficult to persuade the cop plane to take off into heavy
  16. miso

    miso Guest

    The cheap way:
    Ah, the cigarette lighter doubles as a make-up mirror for the ladies.
    Well, I suppose with some caution, but it isn't exactly a mirror. Oh,
    and I tend to build my camp fires when the sun isn't shining.

    But this does seem like a good product to cut your smoking in half.
  17. miso

    miso Guest

    The deal with thermal sensing is your hot object is emitting black body
    radiation, which has long spectrum (spectral?) tails. That is why you
    can view a soldering iron in with some CCD black and white cameras, even
    though the CCD is blind beyond a micron.

    Color cameras have filters over the CCD elements, and they reduce the
    detected IR.
  18. miso

    miso Guest

    Turboprops maintain a steady RPM and vary their prop blade pitch to
    adjust thrust, so I could see a turboprop having a distinct frequency.
    Less so for regular piston aircraft.

    Prior to LED lighting being used outdoors, I think it would be safe to
    assume any flickering light faster than a few hundred Hz would be prop
    reflection. Nowadays it may be more complicated. Even street lights
    these days are LED based.

    Most LEDs are flashed, though the arguments seem endless if DC or
    flashed LEDs are better. Supposedly the eye detects the peak intensity,
    so you can PWM the LED for better effective illumination. But I have
    seen arguments that DC is better.
  19. Hey, fun... Re soldering iron. I've got a little ccd I use to image a
    ~800nm laser. (So no IR filter.) And a weller soldering iron with
    the temperature 'programmed' tips. The CCD can't see the 700 F tip.
    But the 800 F tip stands out clearly. (And my big 200W Weller
    soldering gun is like a torch!)

    George H.
  20. Jasen Betts

    Jasen Betts Guest

    the brain detects peak intensity, the eye average intensity, if it's
    flashing too fast to see you don't see the peak intensity.
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