MQTT OpenTherm Thermostat


Posted on Saturday, September 1, 2018 at 12:00 AM 1506


MQTT Thermostat

MQTT Thermostat is based on OpenTherm Thermostat, OpenTherm Library and ESP8266 controller (WeMos D1 Mini). Can be used for remote heating system control via nodeRED, openHAB, Home Assistant and Android Tasker etc.

Thermostat hardware:

Arduino OpenThrem Adapter Arduino OpenThrem Shield

OpenTherm ESP8266 Adapter Enclosure
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Hardware:

  • DS18B20 Temerature Sensor 1$
  • 8 Pin 2.54mm Stackable Female Pin Header x 2 1$
  • 2 Pin 2.54mm Male Single Row Header x 3 0.30$
  • 1/4 Watt 5% Resistor 4k7 Ohm 0.01$
  • WeMos D1 mini 5$
  • OpenTherm Adapter 15$
  • OpenTherm Shield 7$
  • EMT Electronics RJ12 Phone Socket Enclosure 1$

Software:

MQTT Broker:

As MQTT Broker sample I decided to use CloudMQTT - Hosted message broker for the Internet of Things.
To use CloudMQTT for MQTT Thermostat you need to:
  • Create account
  • Create New Instance (Select a plan(free), name and region)
  • Open instance details and use them in sample sketch
CloudMQTT Details

Sample Code:


#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <OneWire.h>
#include <DallasTemperature.h>

#include <OpenTherm.h>

//OpenTherm input and output wires connected to 4 and 5 pins on the OpenTherm Shield
const int inPin = 4;
const int outPin = 5;

//Data wire is connected to 14 pin on the OpenTherm Shield
#define ONE_WIRE_BUS 14

const char* ssid = "Please specify your WIFI SSID";
const char* password = "Please specify your WIFI password";
const char* mqtt_server = "Please specify MQTT server";
const int   mqtt_port = 00000;
const char* mqtt_user = "Please specify user";
const char* mqtt_password = "Please specify password";

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);
OpenTherm ot(inPin, outPin);
WiFiClient espClient;
PubSubClient client(espClient);
char buf[10];

float sp = 23, //set point
pv = 0, //current temperature
pv_last = 0, //prior temperature
ierr = 0, //integral error
dt = 0, //time between measurements
op = 0; //PID controller output
unsigned long ts = 0, new_ts = 0; //timestamp


void handleInterrupt() {
  ot.handleInterrupt();
}

float getTemp() {
  return sensors.getTempCByIndex(0);
}

float pid(float sp, float pv, float pv_last, float& ierr, float dt) {
  float Kc = 10.0; // K / %Heater
  float tauI = 50.0; // sec
  float tauD = 1.0;  // sec
  // PID coefficients
  float KP = Kc;
  float KI = Kc / tauI;
  float KD = Kc*tauD; 
  // upper and lower bounds on heater level
  float ophi = 100;
  float oplo = 0;
  // calculate the error
  float error = sp - pv;
  // calculate the integral error
  ierr = ierr + KI * error * dt;  
  // calculate the measurement derivative
  float dpv = (pv - pv_last) / dt;
  // calculate the PID output
  float P = KP * error; //proportional contribution
  float I = ierr; //integral contribution
  float D = -KD * dpv; //derivative contribution
  float op = P + I + D;
  // implement anti-reset windup
  if ((op < oplo) || (op > ophi)) {
    I = I - KI * error * dt;
    // clip output
    op = max(oplo, min(ophi, op));
  }
  ierr = I; 
  Serial.println("sp="+String(sp) + " pv=" + String(pv) + " dt=" + String(dt) + " op=" + String(op) + " P=" + String(P) + " I=" + String(I) + " D=" + String(D));
  return op;
}

void setup_wifi() {
  delay(10);
  //Connect to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void setup(void) {  
  Serial.begin(115200);
  setup_wifi();

  //Init DS18B20 Sensor
  sensors.begin();
  sensors.requestTemperatures();
  sensors.setWaitForConversion(false); //switch to async mode
  pv, pv_last = sensors.getTempCByIndex(0);
  ts = millis();

  //Init OpenTherm Controller
  ot.begin(handleInterrupt);

  //Init MQTT Client
  client.setServer(mqtt_server, mqtt_port);
  client.setCallback(callback);
}

void publish_temperature() {
  Serial.println("t=" + String(pv));    
  String(pv).toCharArray(buf, 10);
  client.publish("pv", buf);  
}

void callback(char* topic, byte* payload, unsigned int length) {
  if(strcmp(topic, "sp") != 0) return;
  String str = String();    
  for (int i = 0; i < length; i++) {
    str += (char)payload[i];
  }
  Serial.println("sp=" + str);  
  sp = str.toFloat();
}

void reconnect() {  
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("ESP8266Client", mqtt_user, mqtt_password)) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      publish_temperature();
      // ... and resubscribe
      client.subscribe("sp");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }    
  }
}

void loop(void) { 
  new_ts = millis();
  if (new_ts - ts > 1000) {   
    //Set/Get Boiler Status
    bool enableCentralHeating = true;
    bool enableHotWater = true;
    bool enableCooling = false;
    unsigned long response = ot.setBoilerStatus(enableCentralHeating, enableHotWater, enableCooling);
    OpenThermResponseStatus responseStatus = ot.getLastResponseStatus();
    if (responseStatus != OpenThermResponseStatus::SUCCESS) {
      Serial.println("Error: Invalid boiler response " + String(response, HEX));
    }   

    pv = sensors.getTempCByIndex(0);
    dt = (new_ts - ts) / 1000.0;
    ts = new_ts;
    if (responseStatus == OpenThermResponseStatus::SUCCESS) {
      op = pid(sp, pv, pv_last, ierr, dt);
      //Set Boiler Temperature
      ot.setBoilerTemperature(op);
    }
    pv_last = pv;
    
    sensors.requestTemperatures(); //async temperature request
    
    publish_temperature();
  }
  
  //MQTT Loop
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}


Serial Output:


Connecting to Ihor Melnyk WIFI
.
WiFi connected
IP address: 
192.168.0.77
Attempting MQTT connection...connected
t=23.94
sp=23
sp=23.00 pv=23.87 dt=1.00 op=0.00 P=-8.75 I=-0.23 D=0.62
t=23.87
sp=22
sp=22.00 pv=23.94 dt=1.00 op=0.00 P=-19.37 I=-0.23 D=-0.62
t=23.94
sp=22.00 pv=23.94 dt=1.00 op=0.00 P=-19.37 I=-0.23 D=0.00
t=23.94
sp=22.00 pv=23.00 dt=1.00 op=0.00 P=-10.00 I=-0.23 D=9.37
t=23.00
sp=23
sp=23.00 pv=23.00 dt=1.00 op=0.00 P=0.00 I=-0.23 D=0.00
t=23.00
sp=23.00 pv=23.06 dt=1.00 op=0.00 P=-0.62 I=-0.23 D=-0.62
t=23.06
sp=23.00 pv=23.06 dt=1.00 op=0.00 P=-0.62 I=-0.23 D=0.00
t=23.06    

Android Smartphone MQTT Client:

As MQTT Client for smarphone I've used IoT MQTT Panel.
Because it simple to use and it has nice interface.

MQTT Thermostat Android Interface
To setup IoT MQTT Panel as MQTT Thermostat you nedd to:
  • Create connection and device using CloudMQTT service connection settings
  • Add Gauge panel to visualize current room temperature
  • Add Line Graph panel to monitor temperature history
  • Add Slider panel to set up desired room temperature
MQTT Connection Settings MQTT Gauge Panel MQTT Line Graph Panel MQTT Slider Panel

That's it. Enjoy!

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