Conductivity measuring

Hello,

I tried to find an easy and reliable way of measuring conductivity of water samples but failed by looking on very complicated schematics. I don't want to use voltage divider as it makes more problems than usefull data. Please can you provide me with more information about this topic?

Thanks.

Dragonsired1:
Hello,

I tried to find an easy and reliable way of measuring conductivity of water samples but failed by looking on very complicated schematics. I don't want to use voltage divider as it makes more problems than usefull data. Please can you provide me with more information about this topic?

Thanks.

Conductivity is the reciprocal or resistivity.

Out old circuit board washer measured the resistivity of the water and stopped washing at 1 meg ohm. The new board washer stops washing when the wash water measures 1 microSiemen. Same exact measurement, just different values.

What is your problem with voltage dividers? Somewhere you have to have a range of voltages that an Arduino can measure.

Paul

What is your problem with voltage dividers?

The problem is, that there's too much voltage across probe and electrolysis occurs. First two readings are OK but after some time results vary more than 100%. I found somewhat easy solution with 555 here:
555-conductivity-meter
But the problem is that Arduino would have to then measure frequency which is tricky.
I though about using frequency to voltage circuit or try to make steady current source for let say 25uA and use simple ohms law to calculate voltage with given resistance. What's better idea?

Dragonsired1:
But the problem is that Arduino would have to then measure frequency which is tricky.

To my mind just the opposite of tricky. There are many many examples of using Arduino to measure frequency.

There have been TDS (total dissolved solids) threads on this site.
This one (post#40) might start you off.
Leo..

Dragonsired1:
The problem is, that there's too much voltage across probe and electrolysis occurs.

Yeah, don't use DC.

The problem is, that there's too much voltage across probe and electrolysis occurs.

Even if the voltage is there only for a millisecond?

Wawa:
There have been TDS (total dissolved solids) threads on this site.
This one (post#40) might start you off.
Leo..

That sounds promising! A was doing some research and made that 555timer conductivity circuit. Well it works sort of but DC voltage is still problem. I'm using in my project old PC power supply which has 5+V and 5-V can I make use of it?? I was even thinking about H-bridge and inverters to convert DC to AC. What's the best idea for that?

Dragonsired1:
That sounds promising! A was doing some research and made that 555timer conductivity circuit. Well it works sort of but DC voltage is still problem. I'm using in my project old PC power supply which has 5+V and 5-V can I make use of it?? I was even thinking about H-bridge and inverters to convert DC to AC. What's the best idea for that?

If you feed a square wave with DC component (e.g. 0/5volt) through a (DC blocking) capacitor, then you have a pure AC square wave (+2.5volt/-2.5volt) on the other side.
No need to use a dual rail supply.
Leo..

Another DIY TDS meter, with AC probe, but all analog circuitry.