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You are here: Home » How to Control Multiple Relays With Single Arduino ESP32?

By Abhishek Ghosh September 7, 2019 8:35 am Updated on September 7, 2019

How to Control Multiple Relays With Single Arduino ESP32?

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One regular reader of this website asked us how we can control multiple relays with single Arduino ESP32? This article will not give any direct answer. This is a theoretical article discussing how multiple channels on MQTT can be created so that we can separate matters like temperature and humidity from a DHT11 sensor. Normally we connect DHT11 with IBM Watson IoT in a raw manner. In our that linked guide, it is IBM Watson IoT platform which can separate data and create dashboard visualization. IBM Watson IoT platform and IBM Node-RED are almost bare bone – you can easily run the same setup on a Raspberry Pi or own server. IBM Watson IoT has minimum vendor lock-in. That is said. The Watson IoT Platform has specific requirements on what MQTT topics devices and gateways can use. The Watson IoT Platform is not intended for use as a generic MQTT broker.

How to Control Multiple Relays With Single Arduino ESP32

You can create too difficult things with Cayenne IoT with few clicks but you will get vendor lock-in. It is just a few lines of codes with Cayenne IoT :

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#define CAYENNE_PRINT Serial
#include <CayenneMQTTESP32.h>
 
char ssid[] = "YourNetworkSSID";    
char wifiPassword[] = "networkpassword";  
char username[] = "MQTT_username";   //your MQTT username
char password[] = "MQTT_password";   //your MQTT password
char clientID[] = "CLIENT_ID";       //your clientID
 
const int Relay4 = 14;        
const int Relay3 = 12;      
const int Relay2 = 13;      
const int Relay1 = 15;      
 
void setup() {
  pinMode(Relay4, OUTPUT);
  pinMode(Relay3, OUTPUT);
  pinMode(Relay2, OUTPUT);
  pinMode(Relay1, OUTPUT);
 
  digitalWrite(Relay1, HIGH);
  digitalWrite(Relay2, HIGH);
  digitalWrite(Relay3, HIGH);
  digitalWrite(Relay4, HIGH);
 
  pinMode(LED_BUILTIN, OUTPUT);
  
  Serial.begin(9600);
  Cayenne.begin(username, password, clientID, ssid, wifiPassword);
  Serial.println("Ready..");
  digitalWrite(LED_BUILTIN, LOW);
}
 
unsigned long previousmillis = 0;
int setInterval = 5000;
 
void loop() {
  Cayenne.loop();
  
  unsigned long currentmillis = millis();
  if (currentmillis - previousmillis > setInterval) {
   digitalWrite(LED_BUILTIN, LOW);        
   Cayenne.virtualWrite(6, WiFi.RSSI());  
   digitalWrite(LED_BUILTIN, HIGH);
   previousmillis = currentmillis;
  }
  
}
 
CAYENNE_IN(0)  // action for channel 0
{
  CAYENNE_LOG("CAYENNE_IN_DEFAULT(%u) - %s, %s", request.channel, getValue.getId(), getValue.asString());
  getValue.setError("Error message");
  if(getValue.asInt()) {
    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
    delay(1000);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
    delay(1000);  
  }
}
 
CAYENNE_IN(1)
{
  CAYENNE_LOG("CAYENNE_IN_DEFAULT(%u) - %s, %s", request.channel, getValue.getId(), getValue.asString());
  getValue.setError("Error message");
  if(getValue.asInt()){
      Serial.println("SwitchON 1");
      digitalWrite(Relay1,0); //Device will be SwitchON
    }
  else {
      Serial.println("SwitchOFF 1");
      digitalWrite(Relay1,1); //Device will be SwitchOFF
    }
}
 
CAYENNE_IN(2)  
{
  CAYENNE_LOG("CAYENNE_IN_DEFAULT(%u) - %s, %s", request.channel, getValue.getId(), getValue.asString());
  getValue.setError("Error message");
  if(getValue.asInt()){
      Serial.println("SwitchON 2");
      digitalWrite(Relay2,0); //Device will be SwitchON
    }
  else {
      Serial.println("SwitchOFF 2");
      digitalWrite(Relay2,1); //Device will be SwitchOFF
    }
}
 
CAYENNE_IN(3)  
{
  CAYENNE_LOG("CAYENNE_IN_DEFAULT(%u) - %s, %s", request.channel, getValue.getId(), getValue.asString());
  getValue.setError("Error message");
  if(getValue.asInt()){
      Serial.println("SwitchON 3");
      digitalWrite(Relay3,0); //Device will be SwitchON
    }
  else {
      Serial.println("SwitchOFF 3");
      digitalWrite(Relay3,1); //Device will be SwitchOFF
    }
}
 
CAYENNE_IN(4)  
{
  CAYENNE_LOG("CAYENNE_IN_DEFAULT(%u) - %s, %s", request.channel, getValue.getId(), getValue.asString());
  getValue.setError("Error message");
  if(getValue.asInt()){
      Serial.println("SwitchON 4");
      digitalWrite(Relay4,0); //Device will be SwitchON
    }
  else {
      Serial.println("SwitchOFF 4");
      digitalWrite(Relay4,1); //Device will be SwitchOFF
    }
}

But, you can see that you never learn how the CAYENNE_IN working. The code is enough to get the work done but it escapes the required steps of learning “how I can make it working”.

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---

The reader liked our IBM IoT smart switch guide and ESP32 glass touch buttons.

The answer to the actual question as theory is not that easy. For that reason, I am preparing the readers stage by stage, like how to control a fan over IoT. It is not easy to create a smart switch panel compared to a single smart switch. There are other technical matters, apart from just the code. AC connection is dangerous.

Before we learn to control multiple relays with single Arduino ESP32, we need to learn how to create multiple MQTT channels & fetch data. Code for generic version BME280 sensor module will go like this :

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#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h>
#include <Adafruit_BME280.h>
#include <Adafruit_Sensor.h>
 
// Replace the next variables with your SSID/Password combination
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";
 
// Add your MQTT Broker IP address, example:
//const char* mqtt_server = "192.168.1.144";
const char* mqtt_server = "YOUR_MQTT_BROKER_IP_ADDRESS";
 
WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;
 
//uncomment the following lines if you're using SPI
/*#include <SPI.h>
#define BME_SCK 18
#define BME_MISO 19
#define BME_MOSI 23
#define BME_CS 5*/
 
Adafruit_BME280 bme; // I2C
//Adafruit_BME280 bme(BME_CS); // hardware SPI
//Adafruit_BME280 bme(BME_CS, BME_MOSI, BME_MISO, BME_SCK); // software SPI
float temperature = 0;
float humidity = 0;
 
// LED Pin
const int ledPin = 4;
 
void setup() {
  Serial.begin(115200);
  // default settings
  // (you can also pass in a Wire library object like &Wire2)
  //status = bme.begin();  
  if (!bme.begin(0x76)) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
 
  pinMode(ledPin, OUTPUT);
}
 
void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
 
  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 callback(char* topic, byte* message, unsigned int length) {
  Serial.print("Message arrived on topic: ");
  Serial.print(topic);
  Serial.print(". Message: ");
  String messageTemp;
  
  for (int i = 0; i < length; i++) {
    Serial.print((char)message[i]);
    messageTemp += (char)message[i];
  }
  Serial.println();
 
  // Feel free to add more if statements to control more GPIOs with MQTT
 
  // If a message is received on the topic esp32/output, you check if the message is either "on" or "off".
  // Changes the output state according to the message
  if (String(topic) == "esp32/output") {
    Serial.print("Changing output to ");
    if(messageTemp == "on"){
      Serial.println("on");
      digitalWrite(ledPin, HIGH);
    }
    else if(messageTemp == "off"){
      Serial.println("off");
      digitalWrite(ledPin, LOW);
    }
  }
}
 
void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("ESP8266Client")) {
      Serial.println("connected");
      // Subscribe
      client.subscribe("esp32/output");
    } 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() {
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
 
  long now = millis();
  if (now - lastMsg > 5000) {
    lastMsg = now;
    
    // Temperature in Celsius
    temperature = bme.readTemperature();  
    // Uncomment the next line to set temperature in Fahrenheit
    // (and comment the previous temperature line)
    //temperature = 1.8 * bme.readTemperature() + 32; // Temperature in Fahrenheit
    
    // Convert the value to a char array
    char tempString[8];
    dtostrf(temperature, 1, 2, tempString);
    Serial.print("Temperature: ");
    Serial.println(tempString);
    client.publish("esp32/temperature", tempString);
 
    humidity = bme.readHumidity();
    
    // Convert the value to a char array
    char humString[8];
    dtostrf(humidity, 1, 2, humString);
    Serial.print("Humidity: ");
    Serial.println(humString);
    client.publish("esp32/humidity", humString);
  }
}

You can see that we have two topics :

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client.publish("esp32/temperature", tempString);
…
client.publish("esp32/humidity", humString);
…

Home Assistance is a bigger hammer and there are a lot of tools/platforms such as :

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https://www.home-assistant.io/

I can show you another code to give an idea how to handle multiple relays :

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#include <PubSubClient.h>
#include <WiFi.h>
// #include <ArduinoOTA.h>
 
void callback(char* topic, byte* payload, unsigned int length);
#define MQTT_SERVER "xxx.xxx.xxx.xxx"  //you MQTT IP Address
const char* ssid = "YOUESSID";
const char* password = "WIFI_PASSWORD";
 
const int switchPin1 = D1;
const int switchPin2 = D2;
const int switchPin3 = D3;
const int switchPin4 = D5;
 
char const* switchTopic1 = "/house/switch1/";
char const* switchTopic2 = "/house/switch2/";
char const* switchTopic3 = "/house/switch3/";
char const* switchTopic4 = "/house/switch4/";
 
 
WiFiClient wifiClient;
PubSubClient client(MQTT_SERVER, 1883, callback, wifiClient);
 
void setup() {
  //initialize the switch as an output and set to LOW (off)
  pinMode(switchPin1, OUTPUT); // Relay Switch 1
  digitalWrite(switchPin1, LOW);
 
  pinMode(switchPin2, OUTPUT); // Relay Switch 2
  digitalWrite(switchPin2, LOW);
 
  pinMode(switchPin3, OUTPUT); // Relay Switch 3
  digitalWrite(switchPin3, LOW);
 
  pinMode(switchPin4, OUTPUT); // Relay Switch 4
  digitalWrite(switchPin4, LOW);
 
  ArduinoOTA.setHostname("My Arduino");
  ArduinoOTA.begin();
  //start the serial line for debugging
  Serial.begin(115200);
  delay(100);
 
  //start wifi subsystem
  WiFi.begin(ssid, password);
  //attempt to connect to the WIFI network and then connect to the MQTT server
  reconnect();
 
  //wait a bit before starting the main loop
      delay(2000);
}
 
void loop(){
 
  //reconnect if connection is lost
  if (!client.connected() && WiFi.status() == 3) {reconnect();}
 
  //maintain MQTT connection
  client.loop();
 
  //MUST delay to allow ESP8266 WIFI functions to run
  delay(10);
  ArduinoOTA.handle();
}
 
void callback(char* topic, byte* payload, unsigned int length) {
 
  //convert topic to string to make it easier to work with
  String topicStr = topic;
  //EJ: Note:  the "topic" value gets overwritten every time it receives confirmation (callback) message from MQTT
 
  //Print out some debugging info
  Serial.println("Callback update.");
  Serial.print("Topic: ");
  Serial.println(topicStr);
 
   if (topicStr == "/house/switch1/")
    {
 
     //turn the switch on if the payload is '1' and publish to the MQTT server a confirmation message
     if(payload[0] == '1'){
       digitalWrite(switchPin1, HIGH);
       client.publish("/house/switchConfirm1/", "1");
       }
 
      //turn the switch off if the payload is '0' and publish to the MQTT server a confirmation message
     else if (payload[0] == '0'){
       digitalWrite(switchPin1, LOW);
       client.publish("/house/switchConfirm1/", "0");
       }
     }
 
     // EJ: copy and paste this whole else-if block, should you need to control more switches
     else if (topicStr == "/house/switch2/")
     {
     //turn the switch on if the payload is '1' and publish to the MQTT server a confirmation message
     if(payload[0] == '1'){
       digitalWrite(switchPin2, HIGH);
       client.publish("/house/switchConfirm2/", "1");
       }
 
      //turn the switch off if the payload is '0' and publish to the MQTT server a confirmation message
     else if (payload[0] == '0'){
       digitalWrite(switchPin2, LOW);
       client.publish("/house/switchConfirm2/", "0");
       }
     }
     else if (topicStr == "/house/switch3/")
     {
     //turn the switch on if the payload is '1' and publish to the MQTT server a confirmation message
     if(payload[0] == '1'){
       digitalWrite(switchPin3, HIGH);
       client.publish("/house/switchConfirm3/", "1");
       }
 
      //turn the switch off if the payload is '0' and publish to the MQTT server a confirmation message
     else if (payload[0] == '0'){
       digitalWrite(switchPin3, LOW);
       client.publish("/house/switchConfirm3/", "0");
       }
     }
     else if (topicStr == "/house/switch4/")
     {
     //turn the switch on if the payload is '1' and publish to the MQTT server a confirmation message
     if(payload[0] == '1'){
       digitalWrite(switchPin4, HIGH);
       client.publish("/house/switchConfirm4/", "1");
       }
 
      //turn the switch off if the payload is '0' and publish to the MQTT server a confirmation message
     else if (payload[0] == '0'){
       digitalWrite(switchPin4, LOW);
       client.publish("/house/switchConfirm4/", "0");
       }
     }
}
 
 
void reconnect() {
 
  //attempt to connect to the wifi if connection is lost
  if(WiFi.status() != WL_CONNECTED){
    //debug printing
    Serial.print("Connecting to ");
    Serial.println(ssid);
 
    //loop while we wait for connection
    while (WiFi.status() != WL_CONNECTED) {
      delay(500);
      Serial.print(".");
    }
 
    //print out some more debug once connected
    Serial.println("");
    Serial.println("WiFi connected");  
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
  }
 
  //make sure we are connected to WIFI before attemping to reconnect to MQTT
  if(WiFi.status() == WL_CONNECTED){
  // Loop until we're reconnected to the MQTT server
    while (!client.connected()) {
      Serial.print("Attempting MQTT connection...");
 
      // Generate client name based on MAC address and last 8 bits of microsecond counter
      String clientName;
      clientName += "esp8266-";
      uint8_t mac[6];
      WiFi.macAddress(mac);
      clientName += macToStr(mac);
 
      //if connected, subscribe to the topic(s) we want to be notified about
      //EJ: Delete "mqtt_username", and "mqtt_password" here if you are not using any
      if (client.connect((char*) clientName.c_str(),"mqtt_username", "mqtt_password")) {  //EJ: Update accordingly with your MQTT account
        Serial.print("\tMQTT Connected");
        client.subscribe(switchTopic1);
        client.subscribe(switchTopic2);
        client.subscribe(switchTopic3);
        client.subscribe(switchTopic4);
        //EJ: Do not forget to replicate the above line if you will have more than the above number of relay switches
      }
 
      //otherwise print failed for debugging
      else{Serial.println("\tFailed."); abort();}
    }
  }
}
 
//generate unique name from MAC addr
String macToStr(const uint8_t* mac){
 
  String result;
 
  for (int i = 0; i < 6; ++i) {
    result += String(mac[i], 16);
 
    if (i < 5){
      result += ':';
    }
  }
 
  return result;
}

Now, look at our code for previous guide :

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#define CMD_STATE "/gpio/"
 
// use the '+' wildcard so it subscribes to any command with any message format
const char commandTopic[] = "iot-2/cmd/+/fmt/+";
…

Look at the “Subscribing to device commands” on official documentation from IBM.

We are sending the cURL request like this :

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curl -u <yourApiKey>:<yourApiPassword> -H "Content-Type: text/plain" -v -X POST http://<yourOrg>.messaging.internetofthings.ibmcloud.com:1883/api/v0002/
application/types/<yourDeviceType>/devices/<yourDeviceId>/commands/gpio -d "on"

The last part of the command is important to notice :

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<yourDeviceType>/devices/<yourDeviceId>/commands/gpio

The command is issued against the code :

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#define CMD_STATE "/gpio/"
...

and the line o command topic is this :

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const char commandTopic[] = "iot-2/cmd/+/fmt/+";
 
…

Just with cURL, you can control the whole house. We are communicating with the IoT agent ESP32 directly. We do not need to develop complex Android application. There are few guides on the internet like this one to do that with Sonoff device. IBM compiled Mosquitto in a way to make our work just easy for the server-side.

Tagged With blynk esp32 switch multiple relays , mutiple relay control using adrunio , how to control multiple relays with arduino , how to add multiple relays to one device in cayenne iot , esp32 single chnnel with multiple gpios , esp32 mysql error:109 , esp32 mqtt relay , esp 32 outputs to switch 4 x relays , controlling multiple devices esp32 , arduino multiple relays control

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Abhishek Ghosh

About Abhishek Ghosh

Abhishek Ghosh is a Businessman, Orthopaedic Surgeon, Author and Blogger. You can keep touch with him on Twitter - @AbhishekCTRL.

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    Can ESP32 Used in Commercial IoT Products? Yes, ESP32 has modules and SoC to fit your production need. However, Arduino IDE is not for production.

  • Control ESP32 Arduino LED from IBM Watson IoT

    Here is How to Turn On and Off an LED Connected With ESP32 Arduino From IBM Watson IoT Using Simple Bash Scripts. You Can Use Relay Instead of LED.

  • Controlling AC Powered Appliances With ESP32 and IBM Watson IoT

    It is an upgrade to our previous article to control ESP32 Arduino LED from IBM Watson IoT. We already talked about Android Apps for Watson IoT for this purpose. We already have an article to use relay with Arduino. Our linked relay guide should be enough for anyone to understand how to use relay and […]

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About This Article

Cite this article as: Abhishek Ghosh, "How to Control Multiple Relays With Single Arduino ESP32?," in The Customize Windows, September 7, 2019, January 26, 2021, https://thecustomizewindows.com/2019/09/how-to-control-multiple-relays-with-single-arduino-esp32/.

Source:The Customize Windows, JiMA.in

 

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