I'm just wondering if it would work for long time if used 24/7 underwater, did you already tested?

hi! thanks for sharing your project! where ui can find sketch code?

Hi Brian,

the hardware is now in my hand.

Unfortunately, i clound not find the software :(

Please send me the link

many thanks

Werner

great minds think a like LOL

The Hydro part

https://hackaday.io/project/2964-hydropwnics

The sensing part

https://hackaday.io/project/10457-sunleaf

I'm going to be doing the pH after the next iteration of the sunleaf sensing platform. 

Can you give a bit more info on the pH sensor? They tend to be rather finicky and need regular calibration.

I haven't been using it for long.  I have tried in 2 different environments (freshwater hydroponics tank and a saltwater fish holding pen in a marina), and tested against a stand-alone PH meter, and it is working pretty well.  What I did is an initial test with a PH calibration solution and then did an offset based on what my readings were.  the meter was slightly off, so I did an offset to handle it (see below)

  #define Offset -0.03            //deviation compensate

then in my loop(){}, I did this (where I added the Offset value to my final pHValue).

   static float pHValue, voltage;
   int16_t adc0;
   adc0 = ads.readADC_SingleEnded(0);
   voltage = (adc0 * 0.1875) / 1000;
   pHValue = 3.5*voltage + Offset;

What I am going to end up doing is being able to have a calibration mode that I can put the device into (pressing a button), and then place the device into the calibration solution, which will then update the Offset and store in non-volatile memory.  I figure that I would do this every week or so to keep it in calibration.

sounds good. pH sensors should be kept wet, either in the solution you're measuring or in 3M KCl. they also gradually age and lose sensitivity, so keep an eye on the slope in addition to the offset value; once the slope drops to 90% or so of its original value the probe is probably no longer reliable. Best way to get a good idea of slope is to do _two_ calibrations at different pH levels that bound your expected measurement range, such as 4.0 and 7.0. 

Good advice on the continuing of testing.  I keep my standalone PH sensor always in solution when I am not using it and recalibrate every few months.

On this particular sensor, it is going to be submerged 100% of its lifespan.  Others have noted that this PH sensor is good for about 6 months.  I am going to be using it in two different environments (freshwater for hydroponics and saltwater for Aquaculture).  The saltwater is going to be a bit more harsh, so I figure that I am going to give it about 4 months of lifespan before replacing.  That isn't terrible since having 1,000 fish floating on the surface, because the PH became toxic for them, is much worse than replacing a $40 sensor every few months.