help me abot my project.I want to make a circuit which is measure the conductity of water..thanks

 

Please post more information, two carbon rods from old batteries will do the job.

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Well you can't do it with direct current; you will get a reading for less than a second, then nothing. The reason is that the conductivity is a result of the ions present in solution, and passing DC will alter this.
You need some kind of oscillator (Wein Bridge, or similar) to create a sine wave. Between 1 and 10 kHz seems to work well. Then using this current, and your probes (an audio cord with a gold plated phone plug works well,) measure the resistance of the water.

 

thanks but can ı do this project like phmeter

 

otherway I can buy a probe from shop but I must do a/d inverter etc..can you help more

 

Well, it isn't really like a pH meter. The pH sensor acts like a very small battery; it puts out a very high impedance voltage, either + or -. at pH 7.0, the probe will put out 0.0v. With that one you have to offset, and scale the output.
Which probe were you thinking of? Post a link, so we can look at it.
Like Hero said, more info.

 

pH sensors have very high impedance.
They don't measure conductivity.

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Ron (aka Rube)

 

Whoops, yes that's what I meant. Edited for correctness.
I HOPE I didn't imply this:
but now that I read what I wrote, it kind of does sound that way.

 

I didn't mean to imply that you meant that, but I was aware that it might have sounded like you did. Sorry.

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Ron (aka Rube)

 

Then it's a mother.
no need to apologize, it's all good.

 

Oh, good, I can sleep tonight!

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Ron (aka Rube)