Re: LM34 to A/D

On Thu, 30 Aug 2007 11:45:25 -0700, CptDondo <yan@xxxxxxxxxxxxxxxx>
wrote:

OK, I've got a basic problem. I've got an LM34D (32 - 212 deg F) temp
sensor <http://www.national.com/ds/LM/LM34.pdf> and I need to connect it
to a 0-10V A/D.

To make things more interesting, I am only looking for a relatively
narrow range - say from 50 deg. F to 120 deg. F.

I've got 12 bits of A/D, which, in theory, gives me lots of resolution,
but the LN34 is only good to about a degree. It outputs 10 mV/degree.

The way I read the LM34 spec, the range I am interested in is about
500mV to 1.2V, so I figure I need to amplify that by, say, 8 to get good
use of my A/D accuracy.

I'm mostly a software guy, although once in a while I can solder
something without serious injury.

I've been told I need an op-amp to make the above work, but I have no
idea how to get an op-amp to work in the above scenario.

Could someone please clue me in? Thanks,

--Yan

Why not use an LM71, digital serial SPI temp sensor? By the time you
buy an LM34, and an opamp, and a couple of precision resistors, the
LM71 starts to look like a bargain, and a number of analog gotchas
disappear.

John





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