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PIR sensor runs wild - ideas needed — Parallax Forums

PIR sensor runs wild - ideas needed

robotoroboto Posts: 7
edited 2006-05-16 14:32 in General Discussion
I'm working on a project where I want to detect people approaching certain object, and intend to use the Parallax PIR.

I've tested such unit w/ the basic and advanced demo programs, but it seems to run wild. Sometimes it doesn't detect movement, and other times it keeps triggering when there's no movement. For example, I place the sensor in an isolated spot, triggered the PIR and immediately remove the object triggering it, the O/P just keeps between 0 and 1 for a very long time. It just won't settle.

Any ideas, feedback?

Comments

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-05-16 14:02
    roboto -

    Here are two things to keep in mind, taken from the PIR Sensor Documentation:

    "Once the sensor warms up (settles) the output will remain low until there is motion, at which time the output will swing high for a couple of seconds, then return low. If motion continues the output will cycle in this manner until the sensors line of sight of still again."

    and

    "The PIR Sensor requires a ‘warm-up’ time in order to function properly. This is due to the settling time involved in ‘learning’ its environment. This could be anywhere from 10-60 seconds. During this time there should be as little motion as possible in the sensors field of view."

    Here is something from my own experience, but that experience doesn't extend to the Parallax PIR Sensor per se. At least during the testing and calibration phases, and until you get a good feel for: 1) how sensitive the sensor really is at a distance, and 2) exactly what it takes to fire it off, try to temporarily shield the sensor from any sources of external or ambient infrared energy, or unexpected motion. This includes, but is not limited to any or all of the following:

    Radiant heaters (wall, or floor mounted)

    Residential or commercial sources of environmental heat (cast iron radiators, air registers, baseboard heating units, radient ceiling heat)

    Direct, bright sunlight from windows or skylights

    Air flow from paddle fans, wall fans, or desk fans

    Any source of dust, smoke, or small particulates (burning incense or plug-in, wall mounted heated deoderizer dispensors would be two examples)

    TV or other entertainment infrared transmitters (TV channel changer, etc)

    Many of these items can just be turned off. Some may need to be covered, and other just not used or disabled during this period. Once you have a firm grasp on how the sensor operates in an uninhibited manner, you can add these other items back into the mix, and see if they have any deleterious effect. I was once stymied for over an hour because of a nearby wall mounted, heated deoderizer dispensor, since I had a cold and couldn't smell it each time it fired off and tripped the PIR sensor.

    Regards,

    Bruce Bates

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    Post Edited (Bruce Bates) : 5/16/2006 2:28:53 PM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-05-16 14:32
    Bruce's suggestions are spot on...PIR Sensors respond to changes in the IR/Heat pattern within their field of view.· Any sudden change of that pattern will trigger the sensor.· This could include but not be limited to A/C coming on and changing the air in front of the sensor or·the temperature of a facing wall.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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