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'[EE] Comparing PCB Layouts'
2005\04\18@163947 by Carey Fisher - NCS

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I had a problem and came up with a novel (to me) solution that others
might find interesting ( or it might be common knowledge  :{ )

I needed to compare PCB layouts of two revisions of the same board
to see if required changes had been made correctly.  I also wanted to
make sure no inadvertent changes had been made as has happened
previously.  This was a relatively dense board so I figured out a super
simple way to thoroughly compare two boards:

I downloaded a Blink Comparator program from
http://mysite.wanadoo-members.co.uk/equipnbits/Software.htm. The program is Blink32b.exe.

A Blink Comparator is a device or software that displays two images,
one at a time, blinking between them at a relatively slow rate.  As it
alternates between the two images, objects that are the same in both
images don't change but items that differ between the two images blink
on and off at the blink rate.

This is how Clyde Tombaugh
starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/tombaugh.html
discovered Pluto - he blink-compared photos
of the same place in space until he saw a dot move between photos.  Then
he did a bunch of math and the rest, as they say,  is history.

Anyway, to produce images I could use with the Blink Comparator, I
generated .bmp files using Eagle: File/Export/Image....  I made sure that all
the same layers were enabled.  Note that it's important that both images are
perfectly aligned with each other for the blink effect to work.  Using Eagle, the
two images were automatically aligned.  (Blink32b will also accept .jpg files.)

Then, I started up Blink32b.exe and loaded the image of one layout into Picture 1
and the image of the other layout into Picture 2.  Then just press "Blink On" and
watch differences (and ONLY differences) between the two board blink on and off.
This is really COOL.  You've gotta see it to believe how neat it is.

This may also have application in other areas where eyeball comparison of two complex/dense
objects or images is needed.  For example, you could compare a dense SMT production
board to a "gold standard" board using a digital camera and alignment stand.  Any missing or
incorrectly oriented parts will blink on and off or move between blinks.

There are other Blink Comparator programs on the web but this one seems to be the simplest
and works very well.

Carey Fisher

2005\04\18@174828 by olin_piclist

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Carey Fisher - NCS wrote:
> I downloaded a Blink Comparator program from

I can certainly believe that blinking is a powerful technique, but my first
knee jerk reaction would have been to subtract the two images.  Any
differences should stand out easily.  Did you try this?


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\04\18@180049 by Simon Dyer

picon face
Another method when you have aligned images is to subtract one from the
other - the differences will be the only result in the new image.  Many
packages, like Photoshop or PaintShopPro support the differencing or
subtraction of images using arithmetic operations.

Regards,
--------------------------------------
Simon Dyer, ph +64 3 963 5522
--------------------------------------


{Original Message removed}

2005\04\18@180049 by Simon Dyer

picon face
Another method when you have aligned images is to subtract one from the
other - the differences will be the only result in the new image.  Many
packages, like Photoshop or PaintShopPro support the differencing or
subtraction of images using arithmetic operations.

Regards,
--------------------------------------
Simon Dyer, ph +64 3 963 5522
--------------------------------------


{Original Message removed}

2005\04\18@180938 by Brent Brown

picon face
> I needed to compare PCB layouts of two revisions of the same board to
> see if required changes had been made correctly.  I also wanted to
> make sure no inadvertent changes had been made as has happened
> previously.  This was a relatively dense board so I figured out a
> super simple way to thoroughly compare two boards:
>
> I downloaded a Blink Comparator program from
> http://mysite.wanadoo-members.co.uk/equipnbits/Software.htm.
> The program is Blink32b.exe.

Cool idea. Here's a way of doing this directly in most CAD programs. I'm
using Protel. Load both revisions of the PCB, same view/zoom on each of
course. Press CTRL-TAB (standard Windows function)  to alternate between
windows within the application. It's amazing how often I use this, as it's very
easy to do and is very effective at quickly showing physical changes made
between two revisions.

--
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton 2001, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell/txt: 025 334 069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz


2005\04\18@181042 by Carey Fisher - NCS

face picon face

From: Olin Lathrop
Carey Fisher - NCS wrote:
> I downloaded a Blink Comparator program from

I can certainly believe that blinking is a powerful technique, but my first
knee jerk reaction would have been to subtract the two images.  Any
differences should stand out easily.  Did you try this?

Olin,
It didn't occur to me to subtract the two images.  That would certainly
work.
I do find the realtime blinking useful since it displays the differences in
context
with the entire board.
Carey

2005\04\18@182033 by Andrew Warren

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face
Olin Lathrop <.....piclistKILLspamspam@spam@mit.edu> wrote:

> I can certainly believe that blinking is a powerful technique, but my
> first knee jerk reaction would have been to subtract the two images.
> Any differences should stand out easily.

Yeah, that makes sense for the application at hand (he's comparing
computer-generated PCB plots, right?).  The nice thing about
"blinking" in general, though, is that it works well even if the two
images are different colors -- even negatives of each other -- or
slightly different sizes, or misaligned or rotated, or at different
resolutions... And although subtraction can illuminate any image
additions or deletions, blinking shows -- very clearly -- everything
that's MOVED, too.

-Andy

=== Andrew Warren - fastfwdspamKILLspamix.netcom.com

2005\04\18@184314 by Carey Fisher - NCS

face picon face

----- Original Message -----
From: Simon Dyer
To: Microcontroller discussion list - Public. ; pic microcontroller
discussion list
Sent: Monday, April 18, 2005 5:59 PM
Subject: RE: [EE] Comparing PCB Layouts


Another method when you have aligned images is to subtract one from the
other - the differences will be the only result in the new image.  Many
packages, like Photoshop or PaintShopPro support the differencing or
subtraction of images using arithmetic operations.

---------------------------------------------------------

I also just discovered that IrfanView ( http://www.irfanview.com/)
which is an outstanding, free, graphic viewer, can do blinking
by using the "slideshow" function.  It doesn't, however, seem to be
able to subtract one image from another.
Carey

2005\04\28@061800 by Howard Winter

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Carey,

On Mon, 18 Apr 2005 16:39:46 -0400, Carey Fisher - NCS wrote:

> I had a problem and came up with a novel (to me) solution that others
> might find interesting ( or it might be common knowledge  :{ )

Well astronomers have used blink comparison using purely optical methods for years to find asteroids, comets
and so on, (and it might have been used with WWII reconnaissance photos but I'm not sure).  

Then there was "Howard's Report Comparator" where you needed to compare two computer-output listings (remember
"one-part" listing paper? :-) by placing one on top of the other and holding them against a window to get the
light shining through them, then looking for the differences... although in this case they don't blink :-)

I used to use blink comparison electro-optically to compare program source-code versions (in the days before
source comparators were available) using an editor called Protext, which would allow two programs to be loaded
and by pressing something like <Alt><A> it would flip the display to the other.  Holding down the key
combination used the key-repeat to give the blink.  You could compare two programs in a couple of minutes,
making changes as you go as necessary.  Having each file displayed in a different colour helped, as the
flashes were then colour-coded!

But this is the first time I've seen it suggested for PCB layouts - good catch!

Cheers,


Howard Winter
St.Albans, England


2005\04\28@065027 by Russell McMahon

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> Well astronomers have used blink comparison using purely optical
> methods for years
...
> and so on, (and it might have been used with WWII reconnaissance
> photos but I'm not sure).

It was.


       RM

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