Water conductivity measurement ac, interfacing whit arduino

Hi friends!

I want to implementate this device and the problem is how to correctly build the " read out device" is clearly a wheatsone bridge but in ac, the problem is the signal conditioning for a frecuency between 1-20khz probably I supose that I need to use an OP AMP stage and after a ac to dc meter but the issue is that its needs to be very acurracy. any advices with the opamp stage and the ac-dc convert?

thank you very much!! :wink:

Use an operational amp designed for use with Wheatstone bridges - however many of these have low bandwidths, so the AC frequency may have to be low if you need high gain.

The INA125 is one example often used for load cells and thermocouples, you would use Vref at mid-rail to be able to see full AC waveform. You'll find quite a few examples of using it if you search.

Thank you very much for your answer markT,

I knew about this OP AMP, I bought one but the problem is that most of its aplications are in DC if you see the datasheet in the typical performance curves you can see that close to 1khz the performance goes down because is near his edge, so I belive is not the best amp for this application.

For my limited electronics knowledges the other cuestion is how to convert the DC level from the op amp to a DC level with enough quality I think a diode rectifier is not the best option due to the wave form that result.

any Idea please?

thanks! :wink:

You do not need a great precision and linearity (as the readout device is for zero indication only), do you??

I think I nedd some precision no so great like a expensive device but enough for calibrating and interfacing with arduino, I think that about 5-10% will be great.


A diode rectifier is not suitable for zero voltage detection.... The forward drop of the diode leaves voltages below 0.6V undetected.... Better to use an absolute value amplified (also known as a precision rectifier) The circuit is low cost uses a dual op amp, a few resistors and 4 small signal diodes and will work all the way down to 0 Volts ac.