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From: Gerry Schneider
X-Mailer: Mozilla 4.73 [en]C-SYMPA (Win98; U)
Subject: Re: VERY short range Proximity Sensor
References: <6hKT9.5843$IC6.firstname.lastname@example.org> <3E1FDE58.B49E480A@sympatico.ca> <email@example.com>
Date: Sat, 11 Jan 2003 16:21:13 -0800
NNTP-Posting-Date: Sat, 11 Jan 2003 16:21:04 EST
Organization: Bell Sympatico
> "Gerry Schneider" wrote in message
> > Neil wrote:
> > > Anyone have a schematic for a proximity detector that would be triggered
> > > a hand being placed less than a inch from the antenna?.
> > > All the ones that I find trigger from several feet away.
> > > Thanks in advance,
> > > Kim
> > Turn down the gain or use a smaller pickup antenna.
> > Gerry
> I assume (but may be wrong) that this set up uses 50/60Hz stray fields and
> the receiver reads the strength of this signal and switches on a threshold.
> Would using an oscillator with its own antenna and a receive antenna
> adjacent be an improvement? Set up so that he nearby hand couples the tx
> signal to the rx antenna. Just a thought.
Yes, there is quite a bit of literature about capacitive-based proximity
sensing, and the self-transmitted technique is far more reliable than depending
on stray pickup of power line fields. The MIT Media Laboratory (do a Google
search) is a good starting point for technical papers.
> Local public amenities have a system installed in the hand basins - when
> your hand is within 2" of the side of the basin the water solenoid opens. It
> works quite well - except that the water outlet is offset from the sensor
> too much!
The hand sensing faucets use either infrared beam or capacitive sensing AFAIK.
Look up the QProx QT110 device as an example of a short-range capacitive "touch
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