Proximity sensor?

[harry bissell]

I'd use a light sensor (beam break) you can have the electronics up by the
exhibit, send a beam to a retroreflector (one of those corner prism units they
sell for marking driveways etc.) The retroreflector sends light back exactly
from the direction it came, so alignment is not real critical. This could give
an output that is maintained as long as the person breaks the beam..

IR units are sensitive only to CHANGES in heat signature... if you stand still
they will go off for sure...

Ultrasonics will do the same, but they are sensitive to motions of about 3.3
inches
(assume 40khz) so you have to stand "really still". But they are also
sensitive to air movement etc...  They are "change only" devices also...

I worked in the motion sensor field for a couple of years...

How about a "Tapeswitch" mat hidden under a carpet....  Buy from a local
burgular alarm shop ???

Or if you use the frog approach... illuminate the cell with a hidden laser
pointer... alignment is critical but the beam can travel for many feet without
divergence... and its hard to notice too... We did this to activate a
"halloween" monster at night.

BOO !!!

:^) Harry

Toby Paddock wrote:

> Passive infrared detector?  Like in one of those motion security lights.
>
> Or from one of those plastic frogs that croak at you when you walk by.
> Those really gave my kids the creeps.
>
>  - -- -  Toby Paddock
>
> ----------
> From:   Andrew Schrock[SMTP:aschrock at cs.brandeis.edu]
> Sent:   Wednesday, September 29, 1999 2:53 PM
> To:     SynthFolk
> Subject:        Proximity sensor?
>
> Hi all,
>
> I am currently building a multimedia sculpture (video/sound). It is DIY
> related, actually, since it will have primitive mixing facilities, parts
> of a casio sk-5, parts of a speak&spell, and an analog filter. However, I
> know how to do all that.. my question today is: what do you think is the
> best way to implement a proximity sensor? I was thinking some sort of IR
> switch, but I've always had a bit of trouble with those being reliable. I
> need it to turn the sound on when somebody walks in front of it and go off
> when they walk away. Seems fairly simple, but it has to be rock-solid. Oh,
> did I mention cheap? :)
>
> Also, if anybody has one of those old Apple IIGS monitors, please let me
> know. (the REALLY SMALL green kind which takes composite video input) I
> need one, and the week I decided to go through with this project somebody
> bought the one I had my eye on at the salvation army. Bugger!
>
> later
> Andrew
>
> -| Andrew Schrock | aschrock at cs.brandeis.edu |-