[time-nuts] OT Prototype Boards

[Hal Murray]

bob at evoria.net said:
> OK, I see in the wiki that 0.1" is by definition 2.54mm.  I was taught it
> was 2.54001, but that's not right, either.  But, if industry says that
> they're defined as the same, then I'm the one out of date.  =)  I wonder
> what was with that old prototype board.  I can't find it, so it must be in a
> landfill, but it was just exactly the wrong size to fit a chip.  You could
> get the first few pins in, but then the differences would be enough that no
> more would fit.

I think many many years ago, the metric-inch conversion was slightly off from 
25.4 mm/inch, but that was back before PCBs and it was only off a tiny amount.

Wikipedia's inch article has a history section:
   http://en.wikipedia.org/wiki/Inch#Modern_standardisation
The (a?) old conversion was 39.37 inches/meter.  In 1959, that was changed to 
25.4 mm/inch.

For those of you reading the surveying discussion, there is still a US Survey 
inch using 39.37.  :)

25.4 mm/inch is 39.370078 inches/meter.  That's under 2 ppm from 39.37.  A 50 
pin connector with 0.1 inch spacing would be off by only 0.001 inch.  You 
could probably see or measure that if you looked carefully, but I doubt if 
there would be any problems inserting a part.

----------

I've never had any problems with 0.1 inch spacing.

I have seen problems with surface mount parts that were metric at 0.65 or 0.5 
mm pitch where somebody rounded off too early.  That's easy to do if you look 
at the drawing and use the inch numbers without realizing that you should be 
using the metric numbers.

I just looked at a couple of data sheets.  They omitted the inch numbers for 
the drawings that were really metric.


-- 
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