Alt-BEAM Archive
Message #01307
To: beam@corp.sgi.com
From: Terry Newton wtnewton@nc5.infi.net
Date: Fri, 05 Mar 1999 00:26:39
Subject: [alt-beam] Re: capaciflector
At 09:38 PM 3/4/99 somebody quoted but can't easily discern who wrote
it without stressing:
>>> >be good for a long distance theremin if it's true they can detect from
>many
>>> >feet away.
I don't know what a "capaciflector" is but here's a long distance
object/motion/ghosty detector that is simple, non critical and super
sensitive to many feet. Deceptively simple... (ascii ahead, used fixed)
(220K-?) .-------> + side ----|:|:|:---.
g |d + 9V - |
o---Rg--->|= parallel series or | test
n-jfet |s in place of existing | app
Rs of photocell or switch LED |
(1K) | ^^^ |
`------> - side ----|>|------'
Size of resistor Rs depends on what you hook it too.
On a walker I have a pair in series with the existing CdS-type
photocells, which take the place of Rs. Rg protects from charged
objects and makes a convenient antenna. Value doesn't matter much
just pick something high (mine is 220K) and solder close to the
gate, other end shaped as desired. For the J-FET I have rare TIS-58's
but almost any N channel J-FET will work. MPF102, 2n5457 etc. Drain
and source leads are usually interchangable. In my walker app the
drain goes to +, the source goes to one leg of a photocell, other
leg to a .22uF cap which a microcontroller shorts then times how
it takes to read "high" and eventually controls a microcore with
it. Best effect is how it wakes up when disturbed, even from a
distance and in the dark. If you think hard it might go off.
Hook to a battery and LED as shown (make Rs about 1K) to experiment
with antenna configurations and guage how it responds. Not for
critical steering apps, but influencing a microcore I guess the
chaotic nature of it doesn't matter much and probably helps.
For Who Knows what a microcore thinks. Cheap anyway, have fun...
Terry Newton
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