ARDUINO reef tank controller

I made one of those.  Background I'm a salt water tank enthusiast.  I wanted something sophisticated so I could automate many of the dull tasks. I started with a Arduino Mega as the foundation.  I added an ethernet/SD card shield.  I added PH and TDS probe I2C modules from Atlas Scientific and a RTC module (temperature compensated for accuracy). 

I then built a bus based on RJ45 connectors.  It had 1 serial, 1 1-wire, I2C, and gnd/+5. 

For power, I purchased one of those 8 channel DJ power centers.  It's just a glorified power strip with the ability to manually turn on/off each individual plug.  I created a I2C 8 channel relay module that I piggy-backed on the power center and wired it in. 

For communications, I added two RJ45 jacks wired in parallel.  This allows me to run standard CAT 5 Ethernet between it and the Arduino while leaving a jack free to daisy chain to another power center if I so choose.

On the power center I plugged in the following:

• Main lighting
• Moon light
• Left wave pumps (for wave motion control)
• Right wave pumps (for wave motion control)
• Skimmer
• Heater
• Dosing pump 1
• aux

So in total, I had the following talking to the Arduino:

• 8 channel power
• 1 wire thermometer
• PH
• TDS
• Clock
• Keypad
• LCD

The application ran a sequential timer system along with the LCD update and keypad polling algorithms.  I integrated calibration routines in addition to everything else so I could do the three stage sensor calibrations (low/med/high solution calibration).  As far as the dosing pump goes, it was only doing kalkwasser top offs.  But I could easily done PH adjustments.  But I found the kalkwasser did fine.  The whole thing logged to a simple web page so I could monitor everything over Ethernet.  It stored the logs on the SD card in CSV format so I could dump it into a spreadsheet and view the trends.

Yack yack yack...if you have any questions, let me know.

It is an excellent implementation.

Roger, how did you created the Ph-meter ? I am curious as I have done one but so many years ago that I remembered just now reading your post

I used Atlas Scientific modules.  All you do is solder on a BNC connector and a I2C bus to an Arduino and you can then issue a command to calibrate the new PH probe using three different PH solutions (low/med/high) and you are set!  The module then polls the probe and sends the PH reading back to the Arduino.  It's a smart module as well.  As it polls the probe, it's averaging measurements to get a more reliable reading to compensate for noise.  Atlas makes taking measurements really easy.

Thank you Roger. It sounds strange to me that calibration don't need a precise ... calibrated value but only three average low/med/high. How can it be precise? Is there some trick ?

The three are very precise calibration fluids.  I can't remember the exact numbers.  I THINK they were 2, 7, 10 if I remember correctly.  So, once the device knows which one the probe is immersed in, it knows exactly what the value should be.  Then, it calibrates a curve based on those three.  When you think about it, how would you obtain hundreds of precision PH mixtures necessary to exactly calibrate a PH probe?  For our purposes, it's accurate enough. 

Mathematically 3 points determine a curve or straight line.

Clem,

in the cases of chemical measures - as many other environmental measures - it is not really true. Ph has not always a true linear conductivity variation but follows several kind of curves and there are many parameters that can influence the measure.

Clem,

in the cases of chemical measures - as many other environmental measures - it is not really true. Ph has not always a true linear conductivity variation but follows several kind of curves and there are many parameters that can influence the measure.

No, I understand the nonlinear qualities of Ph. I just stated in Math 3 points are needed to determine if and only if one has a curve (Ph) or a straight line (some linear model). Aw many a angle as well. LOL