At 14:26 27/03/96 -0000, you wrote:
>Hi to any analogue gurus,
>
>I want to use a National Semiconductor LM355 absolute temperature sensor to
>measure ambient temperature.  This 3pin device behaves as a zener diode
>whose voltage is linearly proportional to absolute temperature.  At 25degC
>you get 2.982 volts (=298.2Kelvin), and the voltage changes by 10mV per
>degree.
>
>I want everything to operate on a single rail 5V supply, so I need to put
>the output of the sensor into a circuit which has a gain of about 4, and
>which subtracts about 2.6V from the sensor output first.  This will give me
>a sensible output voltage range which can be read using an ADC (connected to
>a PIC of course!)
>
>It's ages since I've done anything with op-amps and their ilk: can anyone
>help?
>
>Yes I _do_ want to do it with an ADC, I know I could use a Dallas DS1820 and
>do it all digitally, but I have my reasons.
>
>Any help mailed direct to me would be appreciated, or to the list if you
>think others would be interested.
>
>Many thanks,
>
>Andy
>--
>---------------------------------------------------------------------
>Andrew M Errington                               Tel: +44 1524 593678
>Microcomputer Consultant                         Fax: +44 1524 844011
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>Lancaster University                      a.errington@lancaster.ac.uk
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>"A dog is not just for Christmas, there may be some left for
> sandwiches on Boxing Day" - Vladimir Illich Ulyanov 1920
>
>
The only sugestion I can make you is to use the LM35 . It's output is
proportional to the temp. in celsius not kelvin degrees. Using this, you
should not need to substract 2.6 volts. Then you could use an non inverting
amplifier configuration. The LM324 operates using a single rail power suply,
and you can use it.

Ricardo