Hello! I need help with my project and so far I can't get any good results. It would help a lot to get some assistance. My project consists in measuring water conductivity. I can't use dc current because water will undergo elctrolysis so i tought that a square wave current would have good results and it would be very easy to obtain. How can I measure the resistance of the probe using a square wave signal?
The same way as you would as if you were using DC but you only measure the resistance when the squarewave is High
A square wave still has DC. It is just pulsing. So you STILL have the same old problem!
You can expand your idea and use a MOSFET bridge to reverse polarity, this will cancel the polarization. Then measure it on either the forward or reverse direction whichever works best with your circuit. Hint: if the water is flowing the electrolysis should not be a problem. Also if you only turn on the power when measuring that would also help mitigate the electrolysis problem. Slower would be better.
Not if it's an AC square wave as stated in the title
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A simple high-pass filter will take-out the "DC component" allowing the voltage to go negative & positive. DC is "zero Hz" so it can't go through a high-pass filter. The cut-off frequency should be low-enough so the "flat part" of a square wave doesn't drift too-much back toward zero.
Then there are op-amp circuits that you can use to help with reading the "AC" voltage. You can use a peak detector or a precision rectifier. There are half-wave & full-wave versions of both but you should be able to use half-wave and ignore the negative voltages. Or you could build a summing amplifier to add DC bias to the signal.
Note that most op-amp circuits work best with dual (positive & negative) power supplies.
With a voltage divider you mean? Still, the measurements will not be accurate, do you know another method that may give me better results? Aslo the water in flowing so building the circuit in dc would work. Thank you in advance
How accurate do you need?
see this:
Why not just buy a conductivity probe, and use it as intended?
This one works reasonably well and includes test solutions for calibrating the probe.
This one is much cheaper and also works well, but is uncalibrated.
Both use AC excitation, which is just a matter of using alternating port pins as the drive signal.
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