wvmarle:
That's normal. Ground loops. Putting caps in your EC probe connection can help a lot (what probe/sensor are you using for this?) as it stops DC currents. With my EC probe in the water hose and the pH probe in the reservoir I don't have any such issues; haven't yet tried to put the EC probe in the reservoir.No - 5/1024. But you're probably losing a lot of precision here.
First of all: find the ACTUAL voltage range of your pH probe output. There's probably an offset applied, but the output of a pH probe is only about 60 mV/pH point. That's 12 ADC points for 1 pH point shift. You want this offset to be as low as possible, so the highest pH value you measure gives an output close to 0V, and the lowest pH gives an output of <1V.
This way you can use the internal 1.1V reference. Two advantages: much more stable reference voltage (independent from fluctuations in Vcc; your pH probe produces an absolute voltage anyway), and a much better range (1 pH point is now 60 ADC points).
I haven't gotten to messing around with the pH probe yet but I will soon. I am still working on the EC probe. For the EC probe, I am using a regular plug documented here: Plug EC
I am using this probe for pH: pH Probe
I will note your suggestions when beginning pH testing, Thank you.
From what I understand, EC is a lot more sensitive than pH. Given that, it sounds like it's a good idea to use the 1.1V internal reference for EC as well. Have you had luck with this?