Good day!
I will be doing a project wherein it will regularly monitor the conductivity of a liquid(seawater). I will be using a diy probe made from 2 wires 1cm apart. I've read that if DC is used instead of AC, the electrodes will corrode. So I decided to turn on the probe for only half a second at an instance to prevent corroding the electrodes fast. My querry is, can I use the digital pin output to power the sensor instead of the 5v pin of the Mega? Is the current from the digital pin enough for the analog pin?
Thank you!
Can you please give details of how you intend to wire the probe ?
The concept will be like this 
This is exactly what i will be doing....
https://www.google.com.ph/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjRr9-2kM_KAhWDLKYKHUdxDrUQtwIIGjAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D0NPtmHdbW3k&usg=AFQjCNEq7LryitUe6YNxXg87n4LhZrE2Ng&bvm=bv.113034660,d.dGY
Can you please provide a link directly to the YouTube video.
im thinking it as a resistor type sensor, just like the thermistor. With the abundant presence of salts in the seawater, the resistance of water between the 2 wires will be lesser, therefore the analog will read higher values.
Is the output current of the digital pin enough for the analog pins to read?
I think I found the answer....How to stop current draw through Analog Input - Microcontrollers - Arduino Forum thanks!
HappyFeet_jay:
The concept will be like this
I hope this isn't for a saltwater reef tank. If so you need to rethink your electrodes before you poison everything. Even if they aren't powered those screws won't last long in salt water. You need platinum or gold wire for this.
Yup, they will be for saltwater tank. Those nail electrodes are for soil moisture monitor for plants. Im planning to use nickle plated strings as electrodes. They are accesible. Would they do just fine? Or maybe, i'll just buy some platinum wire of from ebay...will the platinum not corrode?
Oh! And im thinking of using a mosfet as a switch for the 5v source of the probe.
Thank you!
This is my 1st arduino project^^...after reading tons of arduino stuff from the net.
Nickel would corrode and be a pretty bad deal for your tank. You want platinum electrodes for the saltwater tank.
Got no other choice. Platinum it is! Thanks! 
Sorry,
Is there a reason carbon (graphite) could not be used?
As it would form carbonic acid at worst...surely this is much better for marine life than heavy metals?
My degree in Chemistry is a bit old at 10years now, but I remember mixing any heavy metals and living things never ended very well.
Graphite is also cheap. Pencils come free from Ikea.
If you use an LM1830, it is specifically designed for the job.
Johnny010:
Sorry,Is there a reason carbon (graphite) could not be used?
As it would form carbonic acid at worst...surely this is much better for marine life than heavy metals?My degree in Chemistry is a bit old at 10years now, but I remember mixing any heavy metals and living things never ended very well.
Graphite is also cheap. Pencils come free from Ikea.
Thanks Johnny, that would be a smart choice. Provided, change of the electrodes will be frequent. But yeah, it is easily accessible, and cheap from pencils! Should i use any pencil or stick to specific brand like mongol?
will the corrosion of the electrodes affect the readings?
bluejets:
If you use an LM1830, it is specifically designed for the job.
thank God you chimed in, bluejets!
Im not well versed with electronics, can you show mo how to wire the LM1830?
which number go to which arduino pin? what pins are for the electrodes. I've read that, it outputs AC so, corrosion of electrodes will be less a problem.
Thank you!