Re: LM34 to A/D

On Thu, 30 Aug 2007 16:08:32 -0700, the renowned John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Thu, 30 Aug 2007 17:59:01 -0500, Spehro Pefhany
<speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Thu, 30 Aug 2007 14:36:16 -0700, the renowned John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Thu, 30 Aug 2007 20:37:05 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:

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.


Pure luxury, at least in my field. We have to make do with diodes and
thermistors. If we were extra good, we get to enjoy a reference chip
alongside. As long as it doesn't cost more than 10c, that is.

Hell, I buy gain-of-four amplifiers for $190 a pop, and single
flip-flops for $32.

John

Don't forget to multiply by 10:1 or 20:1 for the rad-hard versions..


Best regards,
Spehro Pefhany

I wonder what's the most expensive IC you can buy. I've heard that
some high-end FPGA's, not even rad-hard, run close to $10K.

John


The most expensive FPGA Digikey lists is $4,177.00 (6 million gates
and 684 I/O). OTOH, the Fairchild CCD595 is reputed to cost around
100K (81 megapixels).

I guess the most expensive IC is one that has a lot of masks and
doesn't work properly.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Relevant Pages

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