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PIR sensor continues to retrigger with no motion — Parallax Forums

PIR sensor continues to retrigger with no motion

baskervibaskervi Posts: 1
edited 2009-11-30 07:13 in Accessories
I am working on a pretty simple project, but I'm having a problem with triggering. The circuit consists of a 555 timer set up as a monostable multivibrator, and the PIR sensor is set up as the trigger. The PIR sensor continues to retrigger the MSMV even when there isn't any motion. The MSMV output does occasionally go low, but I'd say it is active about 60% of the time.·I've even tried to cover the sensor with a towel, and it continues to retrigger. If I remove the PIR sensor, the MSMV output remains low as I'd expect. I can take the MSMV trigger high, and the output goes high for the expected time, so I'm convinced the MSMV is configured correctly.

Unforunately, I don't have a scope to look at what's going on. Does anyone have any thoughts?

Thanks

Comments

  • SRLMSRLM Posts: 5,045
    edited 2009-11-30 07:13
    Two possible problems:
    1. You may have movement in the area when the PIR is powered on. It uses a bit of time once it is started up to look around and get a base line.
    2. You may be drawing too much current from the output pin of the PIR. Try putting it through a transistor.
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