Yan Seiner wrote:
>
> --- In .com <ts-7000%40yahoogroups.com>,
> Jeff Cunningham < > wrote:
> >
> > Yan Seiner wrote:
> > >
> > > Does anyone have any suggestions for a cheap thermocouple?
> > >
> > > I am looking for something that can be put into a small animal
> > > environment (cage or tank) so it has to be low voltage and visually
> > > unobtrusive; ideally something like the stick-on strain gauges that I
> > > can run DC voltage through, and stick on to some out-of-sight portion
> > > of the tank.
> > >
> > > My plan is to run it into the A/D on one of these boards, and control
> > > heaters based on the input.
> > >
> > > I'm coming up dry with Google; I don't need/want a large, industrial
> > > unit. I need something a homeowner/pet owner wouldn't notice.
> > >
> > > --Yan
> > >
> > What about something like an LM34? Its a 3-terminal temperature sensor
> > that takes a 5v supply and outputs millivolts proportional to either F
> > or C (there's one for each). Use the A/D to convert.
> >
> > http://www.makingth ings.com/ resources/ datasheets/ acc_tmp_001.
> pdf <http://www.makingthings.com/resources/datasheets/acc_tmp_001.pdf>
>
> Thanks everyone, I think I'll take Jeff's suggestion as I have A/D on
> board and an LM34 looks like the simplest thing to do....
>
> So now a question for all the hardware designers out there:
>
> The document that Jeff quoted shows two ways to wire a three-wire
> setup, both on page 7. I can't quite figure out what the difference
> is, which one I should use, and why there are 2 resistors in parallel,
> one 499 1% and the other 22K 5%.... Are they just trying to adjust
> the range of the sensor with the 22K resistor?
>
> What I have is 12 bit A/D that is currently set up for 0-10V; I can
> reduce that down to 0-3.3 if need be. I need to measure normal room
> temps; between 60 deg. F and 110 deg. F to an accuracy of about a degree.
>
> The sensors will be powered from the TS7300 5v supply. It will be
> remotely mounted (up to 10') in a low-noise environment. I have
> shielded twisted pair available which I'd like to use.
>
> Could someone give me clue?
>
> Thanks,
>
> --Yan
>
If you are powering your sensor from the same supply as the sampling
system, you will want to use the left circuit. The one on the left is
missing the comment that the 20k resister should be a pot. The whole
point of that resister pair is to allow you to calibrate the device. The
499 ohm resister gets it in the ball park and the 20k (pot) is used to
fine tune. If absolute accuracy is not that important, you can omit the
20k resistor. They are pretty close as is.
--Jeff
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