- Introduction
- The Hysteresis Controller
- What Else?
- Let's Get it Work
- Auto Mode On
- How does it Perform?
- Next Step
Now comes the fun part of joining all the dots we have been discussing and testing in last seven sections. All we need to do now is to write a simple procedure that will compare ambient humidity against set point and switch humidifier on if it is below or on if it is above the set point.
Before you rush to write this procedure think about humidifier being constantly switched on and off for any swing of humidity. To avoid such situation, it is a common practice to add a dead band below and above the set point and do not operate humidifier if ambient humidity is within the dead band. Exactly the same method of control is used in electric iron or in toilet flush.
The dead band range above and below the set point is called hysteresis. An automatic controller that is working as desribed above is called bang–bang controler or hysteresis controller.
You can experiment what will happen if you have no hysteresis or if you set it to specific value. At this stage, as a starting point, let us assume a hysteresis of +/- 2% RH. Below is a procedure that implements hysteresis controller:
void executeHumidityControl(void)
{
Serial.print("Ambient humidity : ");
Serial.print(humidity, 1);
Serial.print("%, set point : ");
Serial.print(humiditySetPoint, 1);
Serial.print("%, humidifier : ");
if (humidity > humiditySetPoint + 2)
{
// ambient humidity is above the set point
// action : switch humidifier Off
humidifier = LOW;
}
else if (humidity < humiditySetPoint - 2)
{
// ambient humidity is below the set point
// action : switch humidifier On
humidifier = HIGH;
}
else
{
// ambient humidity is within +/- 2% hysteresis
// therefore do not alter current status of humidifier
Serial.print("(No Change) ");
}
Serial.println(humidifier == HIGH ? "On" : "Off");
//
// Operate humidifier connected to RF socket
//
actionTransmitter.sendSignal(1, 'A', humidifier);
}We will finally put into operation the last piece of hardware described under Components, that has not been used so far – the humidifier. It will act as the final element of our control system.
Besides that you will need all the other components used and tested previously.
Speaking in terms of control system, they will act as controller (ESP8266 running the sketch), the input sensor (DHT22) and the output actuator (RF transmitter together with RF socket).
As the HMI - Human Machine Interface we will use a web browser on a PC.
To start with, open previously prepared OnlineHumidifier-Control sketch and save it as OnlineHumidifier-Automate.ino. Then copy the above code of hysteresis controller and add it to the sketch as a separateControl.ino file.
To analyse how controller is performing we need to plot humidity values on a chart. We are already familiar how to do it and have the code ready. Copy the file Emoncms.ino and add it to the folder with OnlineHumidifier-Automate.ino sketch.
Now we need to update OnlineHumidifier-Automate.ino sketch so all these files work together.
To switch controller to auto mode please add handling of additional link as follows:
server.on("/humidifier/Auto", []() {
autoMode = true;
showControlScreen();
});In next step update showControlScreen() procedure to show additional information (controller mode, humidity set point and the new Auto link:
void showControlScreen(void) {
String message;
message += "<html>";
message += "<head><meta http-equiv='refresh' content='20'/><title>Online Humidifier</title></head>";
message += "<body>";
message += "<h3>Humidifier Control - ";
message += (String) (autoMode == true ? "Auto" : "Manual");
message += "</h3>";
message += "<p>";
message += "Humidity : " + (String) humidity + "%<br />";
message += "Humidifier : " + (String) humidifier + "<br />";
message += "Operate : ";
message += "<a href=\"/humidifier/1\">On</a>";
message += " / ";
message += "<a href=\"/humidifier/0\">Off</a>";
message += " / ";
message += "<a href=\"/humidifier/Auto\">Auto</a>";
message += "</body>";
message += "</html>";
server.send(200, "text/html", message);
}You will also need to update the loop() to periodically measure humidity, execute control once it is put into auto mode and send data to Emoncms.org:
void loop(void)
{
server.handleClient();
if (millis() % 20000 == 0)
{
measureHumidity();
if (autoMode == true)
{
executeHumidityControl();
}
sendDataToEmoncms();
}
}Plese note we have reduced period of measurement to 20 seconds. This is done with if (millis() % 20000 == 0) statement.
The last setep is to update procedure sendDataToEmoncms() so it sends to Emoncms.org three additional values: humidity set point, status of humidifier (on or off) and information if controller is in auto or manual mode.
void sendDataToEmoncms(void)
{
if (client.connect(emoncmsServer, 80))
{
String getJSON = "";
getJSON += "GET http://" + (String) emoncmsServer;
getJSON += "/input/post.json?json={";
getJSON += "Humidity:" + (String) humidity + ",";
getJSON += "HumiditySP:" + (String) humiditySetPoint + ",";
getJSON += "Humidifier:" + (String) humidifier + ",";
getJSON += "AutoMode:" + (String) autoMode;
getJSON += "}&apikey=" + apiKeyEmoncms + "\n";
getJSON += "Connection: close\n\n";
client.print(getJSON);
(...)
}You will need to do some additional minor updates like declaration and initialization of new variables and switching the auto mode off if you decide to operate the humidifier manually. For details please refer to complete code in OnlineHumidifier-Automate folder.
Go ahead compile, upload and debug your sketch. Once done, after opening http://IP-of-your-ESP/humidifier/Auto link in web browser you should be able to see a screen as below:
Once sketch is running and ESP is sending data to Emoncms.org, you will soon see new entries under Inputs.
Update configuration of collected data as discussed in section Chart.
Add missing description in column Name under Inputs. Such description will then show up in Feeds and on MultiGraph charts and it helps during data analysis.
Add MultiGraph charts under Dashboards
After completion of the above steps leave your control system running in auto mode for couple of hours. This is to collect data for analysis of performance of your humidity control system. Once you have the data, start tweaking the system and observing how this affects quality of humidity control.
This is fun to observe how control system copes with random disturbances (caused by e.g. opening a window, boiling water in kitchen or washing) and trying to get humidity back to the set point. You may improve time to get humidity back on target by changing hysteresis, output of humidifier, location of humidity sensor and data sampling period.
Consider changing one parameters at a time then collecting data for couple of hours and checking results before moving to next parameter.
In section Maintain I would like to discuss making the code uploads using OTA (Over the Air). This is quicker and more convenient alternative to uploading using a serial port.