Is this the reverse biased method:
http://www.freepatentsonline.com/5955793.html

If so, need a bit longer for this patent to run out (unless you want
to invalidate it, which takes time and money).

It's hard to beat a cheap thermistor for cost, though.  Even Digikey
has $0.57 leaded thermistors in quantities of one, and when you get
down to surface mount you easily halve that cost - in volume they are
very cheap.

Can you give more implementation details on the below method, if it's
not the patented one above?

-Adam

On 5/20/08, Apptech <apptech@paradise.net.nz> wrote:
> >I need a low cost (in qty) way to sense room temperature.
>
> Better with EE tag.
>
> Consulting fee applies when you use the following brilliant
> solution. Pay it to James for PICList support. Lowest cost
> and about highest accuracy is a (silicon) diode with delta
> voltage measurement for delta current step (or vice versa).
> This gives you uncalibrated sensing to well under 1 degree C
> accuracy. Nothing else comes close in effectiveness per $.
> (ducks). Almost nobody seems to use this low cost high
> accuracy calibration free method. In use in some CPU die
> temp sensors. More on this if needed / interested. Note that
> this is NOT the normal "diode as temperature sensor" system
> which is less accurate and requires calibration.
>
> Other:
>
> Thermistor is good. Accuracy varies with $. Calibration
> helps.
>
> Platinum RTD is good but costs more.
>
> Electronic modular solutions.
>
> Thermocouple not really appropriate here.
>
>
>        Russell McMahon
>
>
>
>
> ----- Original Message -----
> From: "Forrest W Christian" <forrestc@imach.com>
> To: "Microcontroller discussion list - Public."
> <piclist@mit.edu>
> Sent: Wednesday, May 21, 2008 1:35 PM
> Subject: [PIC] Low cost temperature sensing
>
>
> >I need a low cost (in qty) way to sense room temperature.
> >I tagged this
> > as [PIC] as I'm looking for a solution which is low-cost
> > when
> > considering interfacing to the PIC processor.
> >
> > Right now I'm bit banging a DS18S20 (had a library) on a
> > PIC18F part for
> > development purposes, but this is a bit pricey and
> > sometimes hard to find.
> >
> > My goals are as follows:
> >
> > 1) 3.3V (this is a biggy-it seems some of the more popular
> > sensors need 5V+)
> >
> > 2) Cheap and easily obtainable.  Mouser stocking it is a
> > plus.
> >
> > 3) No calibration required to obtain accuracy within a few
> > degrees
> > (solder and be done).
> >
> > 4) Ok to use about any resource on the PIC.  I have ADC
> > ins and spare
> > I/O pins available.  The SPI interface is somewhat tied up
> > with a couple
> > of other devices which are fairly high-bandwidth, but I
> > could do a SPI
> > sensor if need be.  I2C not so much, although I guess I
> > could bit-bang
> > i2c as well.
> >
> > 5) Through hole packaging.  No SMD-only parts.
> >
> > 6) -40*F to well over 120*F.  The idea is to monitor
> > likely temperature
> > ranges for outdoor enclosures.
> >
> > Ideas?
> >
> > -forrest
> >
> >
> >
> >
> >
> >
> > --
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