Yes, that is the type of thing I was referring to, I was not saying that a
PIR was being effected by C but that the sensor described was not a PIR.

:)

Justin.

----- Original Message -----
From: "Scott Dattalo" <scott@DATTALO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, February 27, 2001 10:54 PM
Subject: Re: [EE]: Infrared Detector vs Pet


> On Wed, 28 Feb 2001, Jinx wrote:
>
> > > Body's capacitance?  something of the sort.
> >
> > PIRs will work up to quite long distances with the right lens
> > so I doubt if C has much effect. You're looking for an output
> > from the sensor around 1Hz. It can be quite a balancing act
> > making a PIR responsive to humans and not responsive to
> > wafts of cold/warm air
>
> Check out this:
>
> http://www.4qd.co.uk/ccts/pdet.html
>
> It's an e-field sensor (capacitance) that's so sensitive that it can
detect when
> a person enters a room. The circuit was designed in the 70's and as the
web
> says:
>
>      it appeared to be a male circuit as it tended to react
>      more to women than to men. I haven't tested that and
>      suspect it would not be true today. In the 70's women
>      wore more nylon clothing than did men and antistatic
>      fabrics were unknown.
>
>
> You'd be surprised at how easy it is to measure a delta C. Essentially
that's
> what we do at Synaptics (my current employer). We make most of the touch
pads in
> lap tops. In our application, we sense fingers instead of "people".
Proximity is
> obviously a factor. But as the web page I site above indicates, the
technique
> scales. (although our technique is nothing like their's).
>
> Scott
>
> PS. btw, we're hiring If anyone's interested.
>
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>

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