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PICList Thread
'light sensitivity with uncovered window JW part? ('
1999\01\20@143457 by William M. Smithers

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On Wed, 20 Jan 1999, D. Schouten wrote:

> Hi All,
>
> I just read the message from William M. Smithers containing the
> following note :
>
>     (NOTE on A/D code and JW parts: cover the window
>       with something opaque, as light throws off the calibration).
>
> I have always wondered if not covering the window on a JW part with
> some kind of a sticker, could affect any function of the PIC like for
> example the onchip A/D circuit.

Well, I'll tell you how I discovered this, and you can decide for
yourself.  I wrote some code to do 16 bit sampling on the 14000,
hooked it up to a pot for input and had it display the raw 16 bit
unsigned value as an int on the LCD.  With the 14000, you have to
recalibrate frequently (every 16 samples in this case), and I
am keeping a running average of 16 samples, then displaying that
ten times a second or so.

I noticed that whenever I went to trim the pot, before the screwdriver
touched the electronics, the a/d value would drop by several hundred
(a good 8 bits or so).  It took me a couple of minutes to figure
out that my hand was casting a shadow between my bench light and
the chip window whenever I went to touch the pot!

> during software development I always
> leave the window of the PIC clear when testing the application (I hate
> to remove the ever sticking adhesive from window everytime) .

Yeah, I just place another chip over the window, which seems to work
pretty well.

-Will

1999\01\21@055138 by Mark Willis

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For repeated use of /JW parts in prototypes, I figured out a
shortcut;  Snip a little piece of aluminum foil and stick it on with
electrical tape that has a handy tab, you can re-use this a few times,
and it's easy to get off the IC, DO pick a non-obnoxious electrical tape
that doesn't leave stickum on the Quartz, though (not the cheap junk
stuff that has been sitting in a corner for 15 years <G>)

 Mark

1999\01\26@163033 by John Payson

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|For repeated use of /JW parts in prototypes, I figured out a
|shortcut;  Snip a little piece of aluminum foil and stick it on with
|electrical tape that has a handy tab, you can re-use this a few times,
|and it's easy to get off the IC, DO pick a non-obnoxious electrical tape
|that doesn't leave stickum on the Quartz, though (not the cheap junk
|stuff that has been sitting in a corner for 15 years <G>)

It would seem like putting some aluminum foil inside the tape
would allow you to prevent any of the sticky-goo from getting
on the window.  With care, you should be able to make a "flap"
that could be opened/closed without having to stick/unstick
anything.  Interesting concept...

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