Computing stuff tied to the physical world

Another PIR sensor

In Hardware on Mar 17, 2012 at 00:01

Someone drew my attention to a very small PIR sensor on eBay:

DSC 2962

The size is great, of course – but the current consumption isn’t: I measured 1.9 mA idle current @ 5V.

The other inconvenience, in the context of JeeNodes, is that this sensor expects a 5..9V supply voltage.

Using my new accurately adjustable power supply, I was able to establish that it actually works all the way down to 3.6V – with current consumption down to 1.3 mA. But that’s still far from the 50 µA current consumption of the PIR sensor used in the Room Board, so this rules out ultra-low power battery nodes. The detection range is specified as 2 to 3 m, not stellar but probably enough for many uses.

Here are the two sides of this really tiny sensor (whoops, I accidentally cracked the lens):

DSC 2963

DSC 2964

The chip marked 7144-1 appears to be a 4.4V LDO regulator, with excellent < 5 µA idle current and 0.06 V drop-out voltage under light load, but that seems to point to a circuit which really expects to run at 4.4V internally.

I have no idea what this spec means on the eBay page:

Screen Shot 2012 03 11 at 16 38 26

It’s definitely not referring to the idle power consumption of this sensor. Too bad!

Should we try and design our own PIR sensor? I wonder what that would take – some way to stabilize on an average detector level, and then detecting changes in that value? Using an ultra-low power op-amp?

  1. “Should we try and design our own PIR sensor?” …of course And maybe combine it with RF module And maybe the same module make compatible with a pulse LDR sensor :-) Denis

  2. What are the markings on the other two chips?

    Perhaps you can figure out what the “static current <50uA” means from their datasheets?

    You probably checked, but perhaps there is some special way to put them in deep sleep, and get to the <50uA (although, for a PIR sensor, how useful would that be?).

  3. PVDF is also pyro sensitive (as well as piezo active). I found this article to contain several exciting idea’s : http://www.electrooptical.net/www/footprints/fpspie11.pdf

  4. I’ve got me five of these, they also claim to draw less than 60µA, but I measured ~2.4mA@5V. Is everybody lying about the power consumption of these things or are we doing something wrong (although I fail to see what, with a device as simple to connect as this).

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