The easiest way to control automatic irrigation would be using the soil moisture as threshold value and start a pump with that. But I don’t think that this is a suitable approach to control watering of plants. The measuring value coming from the soil probe is rather more a reference point than a value to be used for a controller. I also want to implement a real controller keeping my soil moisture rather constant because I think that will lead to a better yield. The standard controller everybody knows is the PI-Controller. It is an ideal solution for many situations but in my case the disadvantage is that it can only process one measuring value. For sure there are some ways to deal with additional values such as feedforward or cascading but I won’t do that. I will use a Fuzzy Controller instead.
The Fuzzy Controller is a multi-input-multi-output (MIMO) control algorithm working with indistinct (fuzzy) definitions. That sounds very creative but the history goes back to 1965. In the 1990s there was a real hype about Fuzzy Control but then this concept sank into oblivion. In my opinion this control concept is still quite underestimated and unknown today and that’s very unfortunate because it deals well with the most common problems in controller design: no exact model and inly empirical knowledge about the needed algorithm.
I want to use our existing webserver so I will implement the controller in PHP. I have found a very nice class from Wojtek Jarzecji. The idea is that later on an Arduino will call the PHP script. The script will return a change request for the water setpoint (-10%…+10%). The Arduino will add this to the actual pump setpoint (0….100%) and transfer it to a pwm signal.
For the parameters I do some measurements in wet (~400) and in dry soil (~800). Google tells me that in my hometown average humidity is between 50% and 90% and temperature in summer times is between 8°C and 36°C. I take this values to define my input membership functions as follows:
That’s my script:
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<!doctype html> <!--?php require_once ('./fuzzy-logic-class.php'); /*----------------Aktuelle Messwerte aus Datenbank anfragen----*/ // <span class="hiddenSpellError" pre="" data-mce-bogus="1"-->MariaDB Server $servername = "IP-SERVER"; $username = "USER"; $password = "PASSWORD"; $dbname = "templogg"; // Create connection $conn = new mysqli($servername, $username, $password, $dbname); // Check connection if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); } // Actual Values $sql = "SELECT `temp`,`humidity`,`soil` FROM `tbllogging` ORDER BY dt desc LIMIT 1;"; $actual = $conn->query($sql); if ($actual->num_rows > 0) { // output data of each row while($row = $actual->fetch_assoc()) { $acttemp = number_format($row["temp"],0); $acthum = number_format($row["humidity"],0); $actsoil = number_format($row["soil"],0); } } else { echo "0 results"; } /*----------------Fuzzy Parameters----*/ $x = new Fuzzy_Logic(); $x->clearMembers(); /* ---------- set input members ---------*/ $x->setInputNames(array('TEMP','HUMIDITY', 'SOIL')); $x->addMember($x->getInputName(0),'COLD', 0, 8, 25 ,LINFINITY); $x->addMember($x->getInputName(0),'WARM', 20, 35, 100 ,RINFINITY); $x->addMember($x->getInputName(1),'LOW', 0 ,40 ,60 ,LINFINITY); $x->addMember($x->getInputName(1),'HIGH',50 ,70 ,100 ,RINFINITY); $x->addMember($x->getInputName(2),'WET', 0, 400 ,650 ,LINFINITY); $x->addMember($x->getInputName(2),'DRY',550, 800 ,1025 ,RINFINITY); /* ---------- set output members ---------*/ $x->setOutputNames(array('OUT')); $x->addMember($x->getOutputName(0),'LOWER',-10, -5 ,0 ,LINFINITY); $x->addMember($x->getOutputName(0),'RAISE',0, 5 ,10 ,RINFINITY); /* ---------- set rule table ------------ */ $x->clearRules(); $x->addRule('IF TEMP.WARM OR SOIL.DRY OR HUMIDITY.LOW THEN OUT.RAISE'); $x->addRule('IF TEMP.COLD OR SOIL.WET OR HUMIDITY.HIGH THEN OUT.LOWER'); /*---------- Get values from database and calculate output ----*/ $x->SetRealInput('TEMP', $acttemp); $x->SetRealInput('HUMIDITY' ,$acthum); $x->SetRealInput('SOIL' , $actsoil); $fuzzy_arr = $x->calcFuzzy(); $Fuzzy = $fuzzy_arr['OUT']; echo $Fuzzy; ?> |
