>I think the manufacturing processes for surface mount resistors make it 
>easier to come out with 1% resistors economically, or something.

Due to the small price differences in 1% and 5% parts, it is often the 
case that it is easier to just stock the 1% parts.  Manufacturing likes 
it because that's one less reel to retrieve, put into the placement 
machine, remove and restock.  So the extra you pay for the part is 
saved in material and labor burdens.  Purchasing is happy because 
there are that fewer parts to buy.  

> Do people in general call out tolerance on schematics for things like 
> pull-up resistors?  I'd normally only specify a tolerance if that 
> tolerance were actually required.  But then, MY collection of SMT 
> resistors comes from those eBay "partial reel" assortments, and my 
> "about 100k" resistors are actually 97.6k 1% things (and etc.)

As with everything, there is a balance between too little and too 
much information.  Theoretically, the BOM should always include 
the specifics.  Sometimes it is easier for a tech repairing a board 
to just read it off the schematic without having to take the time to 
refer to the BOM.  In that case, you should call out tolerances on a 
schematic.  If desired, to avoid clutter, you could create a text block 
(typically on the first page) that says something to the effect: "All 
resistors 5% tolerance unless otherwise specified".  Similar text 
could be used with capacitors (specify dielectric).

Ken
klumia@adelphia.net


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