Measuring Conductivity with ADC

[fruct0se]

I need to find a way to measure the conductivity or resistance of a liquid using a microcontroller with an output of 5vDC. I also need to use no more than 1vDC to do so.

So far I have tried reducing the output to 0.8v and using an opamp on the ADC input to amplify the return. I cannot seem to get it right no matter what I do. Can someone point me in the right direction on how to accomplish this or show me an example? Maybe I am going about this all wrong? Thanks!

 

[ark5230]

It will be more meaningful if you could add some more information to clarify your actual proble. Any suggestion on altogether new lines could be repeating what you have done in a different area.

 

[FvM]

I guess, you know that conductivity is an AC measurement, if it should have any quantitative relevance?
Thus it involves a somewhat complex circuit: Generator, source/sense amplifier, demodulator or rectifier.

Or are you just designing a kind of level switch without measurement accuracy requirements?

 

[fruct0se]

I need to measure the resistance of a liquid in order to determine the next steps in my program. I have gotten it to work by using 5vDC and using the voltage drop across the liquid to determine the resistance, however in my application I cannot use more than 1vDC to perform the check.

I tried using an op amp to amplify the return but it was very flaky and provided inaccurate readings.

 

[FvM]

DC voltage across the elctrodes causes electrode polarization and electrolysis of the liquid. It can't give reliable results.

 

[fruct0se]

So an AC signal would be the way to go? How would I approach it?