ADC, LM334, & opto isolation

Orion

I need some guidance on a current project involving the above parts.· I am using a PCF8591 to read several LM334s.· The LM334 are wired as show in figure 29.3 http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv29.pdf ··Currently, I have the Agnd @ 2.73 V and the Vref @ 3.43V on the PCF8591, which corresponds to the range of the LM334 (0c – 70c). ·This seems to work fairly well.· Now I want a way too optically isolate the inputs from the rest of my circuit.· What is the best way to achieve this?· Now, my idea is just isolate the I2C buss from the rest of the system.· I would be ok with losing the ADC if the input should take a hit, just not anything else upstream.· Problem is that the power comes from a larger project, and I would like to keep it that way.· If I just isolate the I2C lines, I’m assuming that there would still be a risk that the power supply could be compromised.· What is the best way to isolate the analog input?· How linear will the output be? What complications will this add to calibration?
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LM334 datasheet
http://www.national.com/ds/LM/LM134.pdf·
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PCF8591 datasheet
http://www.semiconductors.philips.com/acrobat_download/datasheets/PCF8591_6.pdf

Orion

Heres a good link to I2C isolation if anyone is interested:

http://www.embedded.com/showArticle.jhtml?articleID=49901764

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