[sdiy] parts watch

[sbernardi at attbi.com]

If you change your input resistors to 49.9K instead of 100K, the rest of your 
circuit could go unmodified.
I'm trying to figure out the pricing on these - $6.31 for 10 meaning they are 
63 cents each? Or is is they are $6.31 each and you have to buy a minimum of 10 
for a total outlay of $63.10?  I think it may only be 63 cents each, since the 
price for the 50 cut tape is $22.36, which would be 44 cents each.
That's quite a bit better than the $4 - $5 apiece we've seen quoted for through-
hole resistor types. 
> Hi Tim --
> 
> Well, that's a bit of an inconvenience.  The attenuation you need is from 
> 100k input resistor
> to just under 1.8k feedback.  That's why we usually look for a 2k feedback 
> resistor with a divider on the output.
> 
> You could go the the voltage divider design and just live with the small 
> amount of tempco shift that gives you, or you could go to slightly smaller 
> input resistors (91k ?).
> 
> Or you could use the design I recently proposed which can easily be 
> modified for just about any resistance and which allows you to dial in the 
> exact tempco.  But you would have to "waste" (gasp) two or three opamps to 
> do that.
> 
>    Ian
> 
> 
> At 12:50 PM 4/28/2003, Tim Ressel wrote:
> >Yo,
> >
> >Well, semi-sharp eyes. Closer examination shows the
> >0805 +3300 resistors top out at 1.8K. This would
> >require a slight change in an expo convertor that
> >calls for 2K. The price is 6.31 for 10.
> >
> >--Tim
> >
> >
> >--- Ian Fritz <ijfritz at earthlink.net> wrote:
> > > Hi Tim --
> > >

> > > Holy cow, how did we all miss that!
> > >
> > > Yes, +3350 is what you need to exactly compensate a
> > > converter.  With the
> > > 10% TC tolerance you will get at most about 250
> > > ppm/K scale drift.  This is
> > > good enough for most people, although a number of
> > > crazy folks like me are
> > > trying to get below 100 ppm/K.
> > >
> > > I would recommend the higher wattage (0805 profile)
> > > to minimize any
> > > possible self-heating effects.
> > >
> > > You could also get the 3900 ppm/K devices and trim
> > > the tempco to the exact
> > > value with a series non-tempco resistor.
> > >
> > > The only problem people might have is that the
> > > minimum order is listed as
> > > 10 pieces.
> > >
> > > Many thanks, Mr. Sharp-Eyes!
> > >
> > >    Ian
> > >
> > >
> > > At 12:05 PM 4/28/2003, Tim Ressel wrote:
> > > >Yo,
> > > >
> > > >I just noticed in the new Digikey catalog some
> > > >Panasonic temco resistors. Sadly they are only
> > > >positive temco, but they have +3300PPM resistors.
> > > Are

> > > >these useable somehow???
> > > >
> > > >Catalog T032 Page 758
> > > >
> > > >--Tim
> > > >
> > > >__________________________________
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