DIY pH, EC and temp monitoring with an arduino, observations so far.

Aloha!

I bought a pH probe, a TDS probe and a waterproof temperature sensor so that i could just look and see rather than open the bucket and dip in to measure. I got code from the net and mixed it together on an arduino, eventually got it all working, temperature compensation etc.

Trouble is, once those probes go in a bucket together things go haywire. Temperature is fine since it's a thermic sensor so it's mechanical and stable, pH is fine along with the temp sensor for compensation, TDS probe is fine along with temp for comp - but you can't use the TDS and the pH sensor at the same time due to electrical interference. If you measure pH in one glass and TDS in another things are fine, so it's not a circuit-power problem, but as soon as they're in the same glass then the pH reading is screwed by the AC field of the TDS probe in the water.

I've read up on shielding one of the probes but no details, i'm thinking i may be able to hook the probe up[ to a MOSFET and just turn it on when needed when the other is off.

Has anyone done this before around here, any experience would be appreciated

One other thing, the main thing really, if you remove the TDS probe from the glass the pH reads fine, so pH and temp work fine together on the bench, but as soon as i put them in the DWC bucket the pH just goes mad, like a random number generator.

I tried removing the circulating pump (i top-feed) and the air pump but pH still mad. I then scooped up a glass of the water from the res and it is just the same, pH all over the place. I stick the pH probe in the calibration fluid and it's bang on.

Is the res water just too alive ?

I'd like to know the answer as well. How large is your res? Have you asked the mfg's of the PH and TDS probes?

Glasses of water from the res read correctly now, they just take a couple of minutes to get a stable reading.
Res reads correctly on average so i'll just take 100 or so samples then display the average.
Only problem now is that the AC field of the EC probe interferes with the pH probe. I put both circuits on their own batteries and the problem persists so it's not a ground loop problem.
I read about some industrial probes that just amplify the pH signal more than the EC signal so i'll try the pH probe on 5V and the EC probe on 3.3.
If that doesn't work then maybe some kind of shielding, a Faraday cage in the water !?

Is it possible to reduce the polling time for the sensors and have them idle in a powered down state, then just alternate the probes coming on for readings? or add a relay board to cut the circuits off when reading the other.

ie system turns on, both probes not powered, sleep 30s, turn on ph probe take reading, turn off, sleep 30s, turn on TDS probe, take reading, turn off, sleep 30s, rinse repeat.

try reading through D1mini i run Tasmota on ESP8266 read through i2c bus it does analog to

Atlas Scientific FTW