[sdiy] parts watch

[sbernardi at attbi.com]

I'm answering my own question: I did a parts search on ERA-S33J, selected 1K 
for the value for cut tape, and it came back with a init price of $.631 for 10.
Gonna get me some!
> 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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