PIR motion detector circuit

All the work is done for you, total of four parts; "working" should be a slam-dunk. But will it work without a lot of false positives, is another question entirely.

If, you can tolerate an occasional false positive it will probably "work." You just have to try different locations and maybe fiddle around with a baffle to limit the beam width to the area of interest.

I have something like that. Looks identical, and I've had it for years to turn on a light in a hallway at night. It works well for that.

Thanks.

Andy

The problem is mostly with PIRs mounted on the house in the winter.

Like other thermal detectors, the PIR measures its own temperature, and not that of the scene. In fact, because of the load resistor across the pyroelectric element, it actually measures a highpass-filtered (AC) version of its temperature.

When it's cold outside, the PIR's temperature is higher than ambient because of thermal conduction from the house via the mounting. A quick gust of wind will cool the sensor, which looks just the same as the ambient warming up.

Cranking the sensitivity down a bit helps, as does a more intelligent AC detection system than just a threshold.

Cheers

Phil Hobbs

The problem is trying to use PIRs outside - period.

Dunno. I've used them outdoors without issues, as long as they're sheltered from the wind in the winter and the sensitivity isn't cranked up too high.

Cheers

Phil Hobbs

Perhaps if they were hooded all round they'd become usable. I've never tried it; might be worth a shot.

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