Another contribution to the Blynk IoT: an HVAC control for my apartment with a 2-pipe heating and cooling system. Hot or cold water is circulated through the radiator system, and temperature is controlled entirely by a fan that blows over the coils. There are no thermostats - just switches - to control the fans. For this project, I’m using a standalone ESP-01, a DHT11 temperature sensor, and a single relay board, at a total cost of less than $10.
About half of the code is just for getting and storing WiFi credentials. The second half contains the thermostat control. My Blynk dashboard is is intentionally simple, with a single control for setting the temperature, and a pair of displays showing desired and actual temperatures. A variety of additional settings (hysteresis, Summer / Winter modes, sensor offset, etc.) can be changed via the Terminal widget. Settings are all stored on the ESP in case of power cycling. A Home / Away mode is included, but is awaiting Blynk location sensing to be implemented.
/****************************************************************************
* HVAC control for a "2-pipe" radiator system.
*
* Compares readings from a DHT11 temperature sensor with desired temperature
* from the Blynk application, and runs the fan unit as necessary to heat or
* cool. Hysteresis levels for both Summer and Winter are independently
* adjustable from 2 to 6 degrees. The temperature sensor readings can be
* offset up or down by up to 5 degrees. All are saved to EEPROM, and
* automatically reloaded on startup.
*
* Some settings are placeholders, awaiting integration of new Blynk triggers
* (e.g. "Home" setting will be toggled by a location trigger).
*
* The hardware is minimal: an ESP-01, a single relay on GPIO 0, and a DHT11
* temperature sensor on GPIO 2.
*
*****************************************************************************
*/
#include "ESP8266WiFi.h"
#include <ESP8266mDNS.h>
#include <WiFiClient.h>
#include <BlynkSimpleEsp8266.h>
#include <SimpleTimer.h>
#include "DHT.h"
#include <EEPROM.h>
//Temperature sensor
#define DHTPIN 0 // what digital pin we're connected to
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);
MDNSResponder mdns;
WiFiServer server(80);
SimpleTimer timer;
//WiFi and Blynk connection variables
char auth[] = "fcd3ba73b3434f728387714b8df65ea0"; // Blynk token "YourAuthToken"
const char* APssid = "ESP8266"; // Name of access point
String st;
String rsid;
String rpass;
boolean newSSID = false;
//Thermostat variables
int TempDes = 70;
int PreviousTempDes = 70;
int TempAct = 70;
int TempCorrection = 0;
int UpdateFrequency = 5000; //Update frequency in milliseconds
float LastRead;
int RelayPin = 2; //Relay pin to turn on fan
int Hysteresis_W = 2; //Summer and Winter hysteresis levels
int Hysteresis_S = 2;
boolean Winter = true;
boolean Home = true;
boolean FirstRead = true; //flag to cycle DHT until a good first read is made
int MenuItem = 0;
// Attach virtual serial terminal to Virtual Pin V1
WidgetTerminal terminal(V2);
void setup() {
dht.begin(); //Start temperature sensor
delay(1000);
pinMode(RelayPin,OUTPUT);
digitalWrite(RelayPin,HIGH);
Serial.begin(115200);
delay(10);
Serial.println("Startup");
Serial.println("");
EEPROM.begin(20); //Get saved temperature correction from EEPROM
Serial.println("Loading presets from EEPROM");
GetPresets();
// if the stored SSID and password connected successfully, exit setup
if ( testWifi()) {
//Frequency of temperature reads and updates from Blynk
timer.setInterval(UpdateFrequency, TempUpdate);
Blynk.config(auth);
while (Blynk.connect() == false) {
// Wait until connected
}
terminal.println("PRESS SETTINGS BUTTON TO ACCESS MENU");
terminal.println("");
terminal.println("");
terminal.flush();
return;
}
// otherwise, set up an access point to input SSID and password
else
Serial.println("");
Serial.println("Connect timed out, opening AP");
setupAP();
}
// WiFi connection ***********************************************************
//****************************************************************************
int testWifi(void) {
int c = 0;
Serial.println("Waiting for Wifi to connect");
while ( c < 20 ) {
if (WiFi.status() == WL_CONNECTED) {
Serial.println("WiFi connected.");
return(1);
}
delay(500);
Serial.print(WiFi.status());
c++;
}
return(0);
}
void launchWeb(int webtype) {
Serial.println("");
Serial.println("WiFi connected");
Serial.println(WiFi.softAPIP());
// Start the server
server.begin();
Serial.println("Server started");
int b = 20;
int c = 0;
while(b == 20) {
b = mdns1(webtype);
//If a new SSID and Password were sent, close the AP, and connect to local WIFI
if (newSSID == true){
newSSID = false;
//convert SSID and Password sting to char
char ssid[rsid.length()];
rsid.toCharArray(ssid, rsid.length());
char pass[rpass.length()];
rpass.toCharArray(pass, rpass.length());
Serial.println("Connecting to local Wifi");
delay(500);
WiFi.begin(ssid,pass);
delay(1000);
if ( testWifi()) {
// Blynk.config(auth);
ESP.restart();
return;
}
else{
Serial.println("");
Serial.println("New SSID or Password failed. Reconnect to server, and try again.");
setupAP();
return;
}
}
}
}
void setupAP(void) {
WiFi.mode(WIFI_STA);
WiFi.disconnect();
delay(100);
int n = WiFi.scanNetworks();
Serial.println("scan done");
if (n == 0)
Serial.println("no networks found");
else
{
Serial.print(n);
Serial.println(" networks found");
}
Serial.println("");
st = "<ul>";
for (int i = 0; i < n; ++i)
{
// Print SSID and RSSI for each network found
st += "<li>";
st += WiFi.SSID(i);
st += " (";
st += WiFi.RSSI(i);
st += ")";
st += (WiFi.encryptionType(i) == ENC_TYPE_NONE)?" ":"*";
st += "</li>";
}
st += "</ul>";
delay(100);
WiFi.softAP(APssid);
Serial.println("softAP");
Serial.println("");
launchWeb(1);
WiFi.softAPdisconnect(true); // kill softAP after completing WiFi connection
}
String urldecode(const char *src){ //fix encoding
String decoded = "";
char a, b;
while (*src) {
if ((*src == '%') && ((a = src[1]) && (b = src[2])) && (isxdigit(a) && isxdigit(b))) {
if (a >= 'a')
a -= 'a'-'A';
if (a >= 'A')
a -= ('A' - 10);
else
a -= '0';
if (b >= 'a')
b -= 'a'-'A';
if (b >= 'A')
b -= ('A' - 10);
else
b -= '0';
decoded += char(16*a+b);
src+=3;
}
else if (*src == '+') {
decoded += ' ';
*src++;
}
else {
decoded += *src;
*src++;
}
}
decoded += '\0';
return decoded;
}
int mdns1(int webtype){
// Check if a client has connected
WiFiClient client = server.available();
if (!client) {
return(20);
}
Serial.println("");
Serial.println("New client");
// Wait for data from client to become available
while(client.connected() && !client.available()){
delay(1);
}
// Read the first line of HTTP request
String req = client.readStringUntil('\r');
// First line of HTTP request looks like "GET /path HTTP/1.1"
// Retrieve the "/path" part by finding the spaces
int addr_start = req.indexOf(' ');
int addr_end = req.indexOf(' ', addr_start + 1);
if (addr_start == -1 || addr_end == -1) {
Serial.print("Invalid request: ");
Serial.println(req);
return(20);
}
req = req.substring(addr_start + 1, addr_end);
Serial.print("Request: ");
Serial.println(req);
client.flush();
String s;
if ( webtype == 1 ) {
if (req == "/")
{
IPAddress ip = WiFi.softAPIP();
String ipStr = String(ip[0]) + '.' + String(ip[1]) + '.' + String(ip[2]) + '.' + String(ip[3]);
s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>";
s += "<font face='arial,helvetica' size='7'>";
s += "<b><label>Hello from ESP8266 at ";
s += ipStr;
s += "</label></b><p>";
s += st;
s += "<form method='get' action='a'><label>SSID: </label><input name='ssid' style='width:200px; height:60px; font-size:50px;'> ";
s += "<label>Password: </label><input name='pass' style='width:200px; height:60px; font-size:50px;'>";
// s += "<p><label>Blynk Token (optional): </label><input name='token' style='width:200px; height:60px; font-size:50px;'>";
s += "<p><input type='submit' style='font-size:60px'></form>";
s += "</html>\r\n\r\n";
Serial.println("Sending 200");
}
else if ( req.startsWith("/a?ssid=") ) {
newSSID = true;
String qsid; //WiFi SSID
qsid = urldecode(req.substring(8,req.indexOf('&')).c_str()); //correct coding for spaces as "+"
Serial.println(qsid);
Serial.println("");
rsid = qsid;
String qpass; //Wifi Password
qpass = urldecode(req.substring(req.lastIndexOf('=')+1).c_str());//correct for coding spaces as "+"
Serial.println(qpass);
Serial.println("");
rpass = qpass;
s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>";
s += "<font face='arial,helvetica' size='7'><b>Hello from ESP8266 </b>";
s += "<p> New SSID and Password received</html>\r\n\r\n";
}
else
{
s = "HTTP/1.1 404 Not Found\r\n\r\n";
Serial.println("Sending 404");
}
}
else
{
if (req == "/")
{
s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>";
s += "<font face='arial,helvetica' size='7'>Hello from ESP8266";
s += "<p>";
s += "</html>\r\n\r\n";
Serial.println("Sending 200");
}
else
{
s = "HTTP/1.1 404 Not Found\r\n\r\n";
Serial.println("Sending 404");
}
}
client.print(s);
Serial.println("Done with client");
return(20);
}
//HVAC Control*********************************************************************
//*********************************************************************************
//Match temp gauge to slider in Blynk app
BLYNK_WRITE(3){
TempDes = param.asInt();
Blynk.virtualWrite(1,TempDes);
}
// Turn the radiator fan on or off
void TempUpdate (){
float ReadF = dht.readTemperature(true);
if (isnan(ReadF)) {
Serial.println("Failed to read from DHT sensor!");
return;
}
if (FirstRead == true){
TempAct = (int)(ReadF + TempCorrection);
FirstRead = false;
Serial.print("First temperature reading (corrected): ");
Serial.println(TempAct);
LastRead = ReadF;
return;
}
else { //Read gets averaged with previous read and limited to 1 degree at a time change
int TempAvg = (int)((ReadF + LastRead + (2 * TempCorrection))/2);
if (TempAvg >= TempAct + 1){
TempAct = TempAct + 1;
}
if (TempAvg <= TempAct - 1){
TempAct = TempAct -1;
}
LastRead = ReadF;
}
Blynk.virtualWrite(0,TempAct); //Report actual temperature in app
Serial.print("Actual temperature (corrected): ");
Serial.println(TempAct);
if (Winter){
if (TempAct < TempDes){
digitalWrite(RelayPin,LOW);
}
else if (TempAct >= (TempDes + Hysteresis_W)) {
digitalWrite(RelayPin,HIGH);
}
}
else if (!Winter){
if (TempAct > TempDes){
digitalWrite(RelayPin,LOW);
}
else if (TempAct <= (TempDes - Hysteresis_S)){
digitalWrite(RelayPin,HIGH);
}
else{
digitalWrite(RelayPin,HIGH);
}
}
if (TempDes != PreviousTempDes){ //update the EEPROM if desired temperature had changed.
EEPROM.write(3,TempDes);
EEPROM.commit();
Serial.print("New desired temperature saved to EEPROM: ");
Serial.println(TempDes);
PreviousTempDes = TempDes;
}
}
// Menu button. Selects settings menu item.
BLYNK_WRITE(V4) {
if (param.asInt()){
MenuItem += 1;
if (MenuItem > 7){
MenuItem = 1;
}
switch(MenuItem){
case 1:
if (Winter){
terminal.println("Mode: Winter / heating. CHANGE?");
}
else terminal.println("Mode: Summer / cooling. CHANGE?");
break;
case 2:
if (Winter){
terminal.print("Winter hysteresis: ");
terminal.print(Hysteresis_W);
terminal.println(" degrees. CHANGE?");
}
else{
terminal.print("Summer hysteresis: ");
terminal.print(Hysteresis_S);
terminal.println(" degrees. CHANGE?");
}
break;
case 3:
terminal.print("Sensor correction: ");
terminal.print(TempCorrection);
terminal.println("degree(s). CHANGE?");
break;
case 4:
if (Home){
terminal.println("Location: home. CHANGE?");
}
else terminal.println("Location: away. CHANGE?");
break;
case 5:
terminal.println("CLEAR WiFi SETTINGS?");
break;
case 6:
terminal.println("RESET THERMOSTAT DEFAULTS?");
break;
case 7:
terminal.println("EXIT SETTINGS?");
}
}
// Move to top of terminal window, and ensure everything is sent
terminal.println("");
terminal.println("");
terminal.flush();
}
//Select button. Executes change of selected menu item
BLYNK_WRITE(V5){
if ((MenuItem > 0) && (param.asInt())){
switch(MenuItem){
//Change season
case 1:
if (Winter){
terminal.println("Mode: Summer / cooling. CHANGE?");
Winter = false;
EEPROM.write(4,0);
EEPROM.commit();
}
else {
terminal.println("Mode: Winter / heating. CHANGE?");
Winter = true;
EEPROM.write(4,1);
EEPROM.commit();
}
break;
//Change hysteresis level of currently selected season
case 2:
if (Winter){
Hysteresis_W += 1;
if (Hysteresis_W > 6){
Hysteresis_W = 1;
}
EEPROM.write(1,(Hysteresis_W));
EEPROM.commit();
terminal.print("Winter hysteresis: ");
terminal.print(Hysteresis_W);
terminal.println(" degrees. CHANGE?");
}
else{
Hysteresis_S += 1;
if (Hysteresis_S > 6){
Hysteresis_S = 1;
}
EEPROM.write(1,(Hysteresis_S));
EEPROM.commit();
terminal.print("Summer hysteresis: ");
terminal.print(Hysteresis_S);
terminal.println(" degrees. CHANGE?");
}
break;
case 3:
TempCorrection +=1;
if (TempCorrection > 5){
TempCorrection = -5;
}
EEPROM.write(0,(TempCorrection + 5));
EEPROM.commit();
terminal.print("Temp Sensor correction: ");
terminal.print(TempCorrection);
terminal.println(". CHANGE?");
break;
//Change location manually
case 4:
if (Home){
Home = false;
terminal.println("Location: away. CHANGE");
}
else {
Home = true;
terminal.println("Location: home. CHANGE?");
}
break;
//Clear stored SSID and password
case 5:
terminal.println("Erasing SSID and restarting unit.");
terminal.flush();
WiFi.begin("FakeSSID","FakePW"); //replace current WiFi credentials with fake ones
delay(1000);
ESP.restart();
break;
//Clear current temperature settings
case 6:
terminal.println("All settings reset to default.");
Winter = true;
Hysteresis_W = 2;
Hysteresis_S = 2;
break;
//Exit Settings menu
case 7:
terminal.println("PRESS SETTINGS BUTTON TO ACCESS MENU");
break;
}
}
terminal.println("");
terminal.println("");
terminal.flush();
}
// Load available presets from EEPROM
void GetPresets(){
TempCorrection = EEPROM.read(0);
if ((TempCorrection < 0) || (TempCorrection > 10)){
TempCorrection = 0;
Serial.println("No saved temperature correction in EEPROM.");
}
else{
TempCorrection -= 5; // 5 was added at EEPROM save to account for negative values
Serial.print("Temperature correction from EEPROM: ");
Serial.println(TempCorrection);
}
Hysteresis_W = EEPROM.read(1);
if ((Hysteresis_W < 2) || (Hysteresis_W > 6)){
Hysteresis_W = 2;
Serial.println("No saved Winter hysteresis in EEPROM.");
}
else{
Serial.print("Winter hysteresis from EEPROM: ");
Serial.println(Hysteresis_W);
}
Hysteresis_S = EEPROM.read(2);
if ((Hysteresis_S < 2) || (Hysteresis_S > 6)){
Hysteresis_S = 2;
Serial.println("No saved Summer hysteresis in EEPROM.");
}
else{
Serial.print("Winter hysteresis from EEPROM: ");
Serial.println(Hysteresis_S);
}
TempDes = EEPROM.read(3);
if ((TempDes < 50) || (TempDes > 80)){
TempDes = 70;
Serial.println("No deisred temperature in EEPROM. Default temp setting: 70");
}
else {
Serial.print("Desired temperature from EEPROM: ");
Serial.println(TempDes);
}
PreviousTempDes = TempDes;
Winter = EEPROM.read(4);
if (Winter){
Serial.println("Season setting from EEPROM: Winter / heating");
}
else Serial.println("Season setting from EEPROM: Summer / cooling");
}
void loop() {
Blynk.run();
timer.run();
yield();
}
And you’re not hijacking the thread. It’s always interesting to see how others approach a similar problem.
