angelcare baby monitor sensor pad

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Just wondering if anyone with a newborn who has those Angelcare baby
monitors with sensor pad.

Has anyone opened up motion sensor pad?  My wife wont let me and I am
dying to know how it works.   There are only 2 wires and I cant
imagine its too hitech but it seems to detect baby breathing movements
through a thick mattress???

http://www.angelcare-uk.co.uk/content/201.pdf


Re: angelcare baby monitor sensor pad


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Never seen one, is it firm to the touch or spongy?

If the former, my guess would be pressure/resistive, if the latter then
possibly an air bladder with passive pressure sensor? Which is cheaper?
Have to watch out for punctures if it's a bladder...

--
Chris.

Re: angelcare baby monitor sensor pad


Its springy. The slightest tap it measures about .4 to over 2v AC for
a sharp tap.  Not sensitive to sound, just heavy vibration. I thought
piezo but in that case wouldnt need  a moving spongy plate which what
this is.
Its designed to set off an alarm if baby doesnt move (breathe) in a 15
sec period.


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piezo's not too good at low freuency. could be a magnetic pickup? is
there any evidence of a permanent magnet - does ant part of it  deflect
a compass needle.




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So it *produces* a voltage without external supply/excitation?


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yes correct, without anypower it produces up to 2v acpeaks .
the pad is 2 splitplastic pads connected together on some sort of
flexible gymbal with a few mm of rocking movement.
I cant open the pad without damaging it.

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I read this as 2 inflexible pads with, my guess, a flexible
piezoelectric film/ribbon (such as
http://www.meas-spec.com/piezo-film-sensors.aspx ) between the two. As
long as the movement never entirely stops there'll be some output (which
is what's required!)

--
FWIW,
Chris.

Re: angelcare baby monitor sensor pad


cth Inscribed thus:

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MIL has a similar device that warns us if she gets out of bed, though I
suspect that its some kind of pressure sensitive device. Its very
similar to an electric under blanket in appearance.

--
Best Regards:
                     Baron.

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Someone is going to use one of these as a kick drum microphone one day.

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How about a big dynamic mic, with the spongy pillow part being the
diaphragm. This would generate a voltage proportional to movement.

Re: angelcare baby monitor sensor pad



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maybe its among this stuff:

http://www.patentgenius.com/assignee/GracoChildrensProductsInc.html



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