[sdiy] Proximity detector

[Toby Paddock]

> --- Fredrik Carlqvist <ifrc at iar.se> wrote:
> > Hi!
> > Does anybody know a circuit for detecting the presence of a
> > human body? Kind of like the ones that open the doors at the
> > supermarket. Preferrably, they would output a voltage
> > proportional to the distance of the body.
> > Fredrik Carlqvist
> 
Tim Escobedo wrote:
> Someone recently posted some info about the QT301 chip. 
> ...

http://www.seanet.com/~tpaddock/c2cv.html
I don't know if it will get the distance 
you need. I just tried it with the QT301 
and a 3 foot wire stretched out 
horizontally. It would start to see me at 
about 16 inches and was kind of jittery. 

BUT,
I tried the QT300, which is 16 bit serial 
output, instead of 8 bit PWM 'analog'. 
It would start to see me at about 24 inches 
and seemed to have a nicer response. I 
don't know mutch at all about the QT300 and 
I don't know how to talk serial. 
(The evaluation board does both chips and 
has an lcd display.) Yet another reason I 
need to learn about microcontrollers.

I didn't try tweaking the sensitivity 
capacitor (the eval board has 100nF) or 
antenna style. Might be able to squeeze 
out some more distance.

Later,
Toby
Paddock