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Passive IR Motion Detector output floats between off and on state — Parallax Forums

Passive IR Motion Detector output floats between off and on state

MikeDodaroMikeDodaro Posts: 9
edited 2011-11-06 12:05 in Accessories
I have the motion sensor part# #555-28027.
I've tried this part both with a pull up resistor on the + side and without the pull up resistor, and the results are the same. The output floats between off and on state. What am I missing?

Comments

  • ElectricAyeElectricAye Posts: 4,561
    edited 2011-11-02 14:04
    Welcome to the forum.

    Do you have a resistor between the output and ground?
    If I remember correctly, it sometimes helps to have something like a 10K resistor between the output signal and ground, and be sure to have the grounds connected between your sensor and your other devices.
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 14:15
    That sounds like a pull down resistor on the ground side. I'll give it a shot.
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 14:27
    Same result. The output floats between off and on.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2011-11-02 15:51
    Mike,

    are sure you have the sensor aiming at something that is cool and stable? These types of sensors can be sensitive to changes in IR light, changes such as sunlight flickering through the leaves of a tree, or a distant source of fire, like a distant campfire, flickering because of the wind or because of reflecting ripples on water. Even ceiling fans, etc. can sometimes cause them to go off because some unseen source of IR is being flickered by the moving air. Also, if the sensor is aiming at something reflective in the IR spectrum and you're behind the sensor and moving around, the sensor might see your reflected body heat.

    What is the sensor aiming toward?
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 16:04
    I've tried it several ways. In my office it points straight up. It's possible my computer is affecting it, so I tried it in another room and went away. I have it in a circuit with a led that lights in the high state. After leaving it in an empty room for a while, I came back and it was still flashing on and off.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2011-11-02 16:50
    MikeDodaro wrote: »
    ....I have it in a circuit with a led that lights in the high state. After leaving it in an empty room for a while, I came back and it was still flashing on and off.

    Can you post the schematic or maybe a photo of the circuit? Maybe it has something to do with how the LED is being driven. What are you using for a power source?
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 17:17
    The circuit is powered by 3.3 volts from a GHI Electronics Spider Mainboard. Connections are on a bread board. I've used USB power and battery power with similar results. I've seen it settle down now a few times and work properly on motion, but it bounces for several minutes after each stimulus. I think it is working, but glitchy.

    The circuit is just + to +, ground to -, and out to a pin on my connector socket, which I know is working from other uses.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-02 17:29
    I know this device is supposed to work for Vdd between 3V and 6V, so 3.3V should be okay (assuming that's actually what your supply is putting out). But have you tried running it from, say, 5V just to see if it behaves differently?

    -Phil
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 17:48
    What is the voltage of output? The Input pin on my logic circuit is supposed to be 3.3 volts.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-02 18:46
    Disconnect it from your input pin for the test at a higher voltage, and watch the output on a scope if you have one. The objective is to see if the sensor is functional at a higher voltage -- not to see, initially, if it will work in your circuit. Also, make sure that the 3.3V supply you are using really does supply the stated voltage, not something lower. These are the very basics. Once those have been established, you can get back to the "floating" issue.

    -Phil
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-02 21:15
    Thanks, Phil. But, I don't have a scope. I'm a software guy trying to get a grip on this kind of thing. I think it would be difficult to get a voltage reading with the $25 meter I have from Radio Shack. The voltage of the Spider mainboard is well tested, and I have used it with a similar implementation using a phototransistor instead of this motion sensor.
  • SRLMSRLM Posts: 5,045
    edited 2011-11-02 23:38
    A multimeter might be enough to help debug the circuit. I would suggest that you hook the PIR up on it's own breadboard with the multimeter connected to the output and ground, set on voltage reading. Before you turn it on cover it up with a cup or something IR opaque, don't move it, and watch to see what the output does.

    A write up that I did a number of years ago, here might help (although all the pictures got lost in the forum migration): http://forums.parallax.com/showthread.php?109337-PIR-General-Activation-Circuit

    The missing schematic from the link:

    100_0140.jpg
    100_0140.jpg
    1024 x 576 - 49K
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-03 09:12
    I'll have to get some more parts to try this and there are a couple of meetings today to deal with. I'll get back.
  • MikeDodaroMikeDodaro Posts: 9
    edited 2011-11-06 12:05
    I noticed that the onboard LEDs on this part never lit up, which was odd because it was hyperactive about motion. I took it back to Radio Shack for an exchange in case it was defective. A couple of days later I went back to get the exchange they ordered. Now I know why the part was acting so flakey. I'll leave it up to Parallax to own up.
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