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PIR triggering at regular intervals — Parallax Forums

PIR triggering at regular intervals

fadecomicfadecomic Posts: 6
edited 2014-10-31 12:56 in Accessories
Hi,

I have a Parallax PIR sensor from Radio Shack, and it is behaving oddly. If I rig up a very simple circuit--i.e. 5V, GND, and a LED (with resistor of course), the LED begins to flash very regularly. It's not random. It's almost like a timer. This is, needless to say, unexpected. Anybody else have this experience? If so, what might it mean?

Thanks

Comments

  • fadecomicfadecomic Posts: 6
    edited 2014-10-29 13:58
    Well, I just noticed that flashing while motion indicates "non-retriggering" mode. Which seems to indicate that my PIR thinks something is always moving.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-10-29 16:14
    What is the power supply? What is the sensor facing? It can take up to 60 seconds of no changes in the IR field in its FOV for it to settle.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2014-10-29 16:16
    fadecomic wrote: »
    Well, I just noticed that flashing while motion indicates "non-retriggering" mode. Which seems to indicate that my PIR thinks something is always moving.

    That's quite possible. One culprit could be air. These types of sensor detect changes in thermal bodies, and wafting air from a window or heat vent, can do it.

    For obvious reasons, the sensor itself cannot be moving, or even held in your hand. It must be stationary.

    Try testing the sensor in a different room. You don't mention what you're using for the 5V. It should be a nicely regulated and stable power supply.
  • fadecomicfadecomic Posts: 6
    edited 2014-10-30 11:47
    Chris Savage wrote: »
    What is the power supply? What is the sensor facing? It can take up to 60 seconds of no changes in the IR field in its FOV for it to settle.

    It's a 5 V power supply, regulated by an LM7805 with all the proper caps. The sensor is facing the ceiling, but I've also tried covering it completely. The blinking pattern doesn't start right away. It's difficult to tell for certain, but it seems like it happens after the first time the sensor triggers.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-10-30 13:30
    I'm not clear. What triggers it the first time (what is the source)? And are you saying once triggered it just keeps cycling until power is removed?
  • fadecomicfadecomic Posts: 6
    edited 2014-10-30 13:34
    What I mean is that the cycling doesn't happen right away. It seems to go through the warm up period and then it starts cycling. Possibly after detecting motion, because it seems to happen after I wave in front of it. I'm not 100% certain that's not coincidence, however. In any case it definitely starts after some delay after power is supplied.
  • Hal AlbachHal Albach Posts: 747
    edited 2014-10-30 16:39
    Is your sensor a Rev A or Rev B? For rev A the jumper at the upper left corner controls triggering, for rev B the jumper controls sensitivity. For rev B the output pin can source up to 23 mA, the rev A requires a transistor or mosfet to drive a load.
  • fadecomicfadecomic Posts: 6
    edited 2014-10-30 20:07
    Hal Albach wrote: »
    Is your sensor a Rev A or Rev B? For rev A the jumper at the upper left corner controls triggering, for rev B the jumper controls sensitivity. For rev B the output pin can source up to 23 mA, the rev A requires a transistor or mosfet to drive a load.

    Wasn't sure which rev, but yep, that was it. Works like a champ now. Thanks.

    It's worth noting that a 2n3904 did not work, but a MOSFET (I had an IRF520N sitting around) did. The 3904 gave the same results as no transistor. Perhaps with a large resistor it would work, but I didn't try that.
  • Hal AlbachHal Albach Posts: 747
    edited 2014-10-31 10:37
    How big of a base resistor did you use with 2N3904? I would think anywhere between 5K and 10K should work. Too low and the base will load down a high impedance output.
    The difference between Rev A and Rev B is that the Rev B module will say "Rev B" to the right of the dome, opposite from the jumper.
  • fadecomicfadecomic Posts: 6
    edited 2014-10-31 12:56
    Hal Albach wrote: »
    How big of a base resistor did you use with 2N3904? I would think anywhere between 5K and 10K should work. Too low and the base will load down a high impedance output.
    The difference between Rev A and Rev B is that the Rev B module will say "Rev B" to the right of the dome, opposite from the jumper.

    I will try this evening before the trick-or-treaters show up and let you know how it goes. I honestly don't remember which one I grabbed.
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