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A different kind of motion sensing security light?

Discussion in 'Electronic Basics' started by John Doe, Feb 3, 2013.

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  1. John Doe

    John Doe Guest

    Correct me if I'm wrong on any of this, but... The motion sensor
    (part) output constantly varies. Only when its output reaches a
    certain level relative to its normal state, then it trips a switch
    that drives the light for some period of time. Then the lightbulb
    switches off and waits for another significant change in

    What I would like to do is have a lightbulb or LED
    brightness/intensity follow the motion sensor output part. In
    other words... If a bird flies by, the lightbulb would momentarily
    dimly light. If a person walks into close range, the lightbulb
    would continuously shine brightly. If the person walked behind
    some object, the lightbulb would go off, and then when they
    reappeared, the lightbulb would come back on. Hopefully I'm not
    over describing this, but I'll be happy to provide more
    description if asked.

    Does such a device (or close) already exist for purchase in a

    The sensor output part typically could not be connected to an LED
    without putting an amplifier on it? Anybody do this before, any

  2. Jamie

    Jamie Guest

    look at ultrasonic distance sensors. You can get outputs that
    are analog for a distance reading of an object infront of it or
    a switched output when an object is with in range.

  3. Tim Williams

    Tim Williams Guest

    AFAIK, pyroelectric sensors are a "single pixel" sort of thing, so they
    don't know if the scene is moving, only if the average IR changes. Which it
    does when someone comes into view or jumps out of the shadows, but it
    doesn't do jack if someone walks around freely while holding up a
    room-temperature blanket, or moves in the scene while presenting an equal
    viewing cross section (probably tricky to do).

    The output is positive or negative charge, corresponding to the change in
    temperature viewed. Into a high resistive load (say, like something Phil
    might be working on right now :) ), this has a time constant (the sensor's
    just an insulating crystal), so it automatically centers after a while. In
    other words, it's a temperature differentiator (for pedants, that's the RC
    kind). Obviously, a motion detector needs only a window comparator; you
    could use a suitably calibrated gain instead (followed by a full-wave active
    rectifier), and maybe a lowpass, or falling slew rate limiter, to enhance
    the effect.

    Still might not be quite as intended; if the detector response is equal
    across the viewing angle, then a person walking across the path will cause
    it to light up (or down), then not do so much (depending on how the sensor
    sees a walking body), then light up again on leaving the frame.

  4. John Doe

    John Doe Guest

    That's all I want. It's not going to be the only part of the
    system, and I can interpret the output. I guess it could even be a
    very short (1 second or less) on time by a common passive infrared
    motion detector, so that it would flash during its detection time.
  5. harry

    harry Guest

    You can buy sensors that have a restricted/adjustable "target" size.
    To eliminate nuisance operations from small animals.

    There will always be an amplifier and relay in the circuit.
  6. Guest

    I doubt he's going to find a finished product that does what
    he wants. The products ready to be mounted have not
    only the sensor, but as he points, out the circuitry that
    turns it into some kind of on/off output that is needed for
    the product.

    However those motion detector products use ICs which
    he can probably find. Some of the ICs provide an analog
    output that he could use together with his own circuit.
    Here are examples from one company:
  7. Guest

    Wrong yet again. harry is like a cosmic black hole of ignorance, no
    real knowledge can exist anywhere near him.
  8. Mark Zenier

    Mark Zenier Guest

    They're two "pixels" in an AC coupled differential circuit.
    The optics are set so that the sensors see adjacent areas and
    react to fast changes. (You can fool them if you move real slow).

    The best analogy of the optics is to spread your fingers apart and put the
    flat of your palms together so that the fingers interleave. One sensor
    per "hand", with the views of the two sensors interlinked. Any movement
    quick enough, and one sensor will decrease while the other increases.
    The response is usually flat in one plane, determined by the way the
    plastic lens is molded.

    Radio-Electronics/Electronic Now magazine had a long distance pyroelectric
    sensor project that used a motor driven mechanical chopper, back when
    these things were new.

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
  9. Jamie

    Jamie Guest

    we used a few of those for wire break and jerk detectors just as the
    conductor comes out of the induction heater and prior to entering the
    extrusion head assembly.

    Since the conductor will jerk with a over sized section going through
    or a breakage, it works out well. There is also a small air jet that
    sits infront of the IR passive glass to keep the dust off.

  10. SoothSayer

    SoothSayer Guest

    One must also be *VERY* careful when handling/installing the device as
    well. They usually come with shorting wires on the leads they are so

    Some FETs can be blown by an ESD field, particularly prior to being
    installed. Does not even require contact.

    That is why a smock is required at the 'proper' ESD safe workstation.
    It 'contains' whatever fields you and your insulative clothing may be
  11. John Doe

    John Doe Guest

    I guess that means there is no analog output. So it's not like a
    photo resistor. I've played with photo resistors, controlling a
    variable frequency connected to a speaker. Aiming it towards a TV
    produced amusing and rapidly changing frequencies. I wonder if
    there are hypersensitive photo resistors that might do (with a
    wide field of view), maybe infrared or whatever. Or maybe that has
    already been suggested under different terminology.
    I don't need to know distance or speed. All I want to sense is
    changes in radiation in the area. But if the changes in intensity
    are great, that might suggest the object is either large or
    nearby. I guess that would be a function of something like a
    long-range omnidirectional (or wide angle, as long as it's view is
    not narrow) infrared photo resistor/sensor if there is such a
    thing. I'll look.

    Distance to sense a person, to noticeably and distinctly change
    the output, needs to be at least 20 feet, preferably 50-100.
  12. mike

    mike Guest;..0.0...1c..2.serp.z6TfNc9RhwA
  13. John Doe

    John Doe Guest

    To be clear...
    actually, what I played with might be called a photodiode (not a
    photoresistor), it looked like an ordinary white LED, it didn't have
    the squiggly wires inside
  14. John Doe

    John Doe Guest

    I will plan to use that, that will be easiest. I will see if the
    output can be made to flash a light as long as motion is being
    detected, without a long delay or long on-time.
  15. Jasen Betts

    Jasen Betts Guest

    these sensors detect movement by having two "pixels" that are focused by
    the lens onto alternating bands of the scene, the sensors only produce
    a signal proportional to the rate of change of average temperature of
    the area viewed by the pixel.

    a person walking across the fiels od view would produce a signal that
    alternates between the two sensors.
    I've not heard of one.
  16. Robert Macy

    Robert Macy Guest

    If you're going mechanical, why not make it a capacitive sensor.
    Chopping the field from the intruder. Since you kknow the speed of the
    chopping, you can synchronously detect and obtain EXACTLY the type of
    signal you want. ...I think.
  17. John Doe

    John Doe Guest

    Google produces 280 results for my "Tonal Voltmeter". I'm sure it
    was just that, using a photodiode to vary resistance/voltage. It
    looked like a clear T1 LED. I have nothing left (except fond
    memories) from experimenting with electronics.
  18. John Doe

    John Doe Guest


    As I said in two prior separate replies... I am FWIW satisfied
    with the discussion. I will probably use a cheap motion detector,
    and maybe try to shorten the on-time so that the light blinks
    while motion is being sensed.

  19. Jamie

    Jamie Guest

    That's strange that you would call them thermistors? TO me a thermistor
    is a slow reacting device? But yet we have an application where we use a
    basic pyroelectric 3 wire detector for detecting vibration of small
    conductor as it exits from an induction heater. This vibration can get
    up to around 1khz or more when the wire snaps for what ever reason.

    I would think a thermistor device would be a little slow for this
    wouldn't you?

    Maybe the units I used have different smoke in side.

  20. Jasen Betts

    Jasen Betts Guest

    AIUI they are closer to capacitor than resistor, the device does sense
    its own temperature though, they detect remote temperature by
    black-body radiation changing the temperature of the sensor.

    TO me a thermistor
    if you could make it thin enough it would work.
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