How To Easily Create Android App Controlled Local Devices With ESP32

For DIY IoT setup, we already have guides with IBM Watson IoT. In those guides, we have mentioned an Android App named “HTTP Shortcuts” for making the thing a bit smarter and professional.

You’ll not need to set up IoT to only locally control a device, for example, a water pump probably does not need control over the internet. In these cases, you only need Wi-Fi. Here is the code snippet for ESP32 to create a relay-based control via Wi-Fi. The relays are attached to pins 19, 21, 22, and 23. I have also have the sketch on GitHub as a repo for you.

I am not providing circuit diagrams because it is just easy to attach a 4 channel relay module with ESP32. You can simply attach LEDs for testing purpose.

#include 
 
// Replace with your network credentials
const char* ssid     = "your ssid";
const char* password = "your password";
 
WiFiServer server(80);                                     // Set web server port number to 80
 
String header;                                             // Variable to store the HTTP request
 
const int relay1 = 19;                                     
const int relay2 = 21;
const int relay3 = 22;                                     
const int relay4 = 23;
const int LED = 2;
 
 
void setup() 
{
  Serial.begin(115200);
 
  pinMode(relay1, OUTPUT);                               // Initialize the output variables as outputs
  digitalWrite(relay1, LOW);                             // Set outputs to LOW
 
  pinMode(relay2, OUTPUT);                               // Initialize the output variables as outputs
  digitalWrite(relay2, LOW);                             // Set outputs to LOW
 
  pinMode(relay3, OUTPUT);                               // Initialize the output variables as outputs
  digitalWrite(relay3, LOW);                             // Set outputs to LOW
 
  pinMode(relay4, OUTPUT);                               // Initialize the output variables as outputs
  digitalWrite(relay4, LOW);                             // Set outputs to LOW
 
  pinMode(LED,OUTPUT);
  digitalWrite(LED,LOW);
 
  // Connect to Wi-Fi network with SSID and password
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  // Print local IP address and start web server
  Serial.println("");
  Serial.println("WiFi connected.");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
  server.begin();
}
 
void loop()
{
  WiFiClient client = server.available();   // Listen for incoming clients
 
  if (client) // If a new client connects,
  {                             
    Serial.println("New Client.");          // print a message out in the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected()) // loop while the client's connected
    {            
      if (client.available()) // if there's bytes to read from the client,
      {             
        char c = client.read();             // read a byte, then
        Serial.write(c);                    // print it out the serial monitor
        header += c;
        if (c == '\n') // if the byte is a newline character
        {                    
          // if the current line is blank, you got two newline characters in a row.
          // that's the end of the client HTTP request, so send a response:
          if (currentLine.length() == 0) 
          {
            // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
            // and a content-type so the client knows what's coming, then a blank line:
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println("Connection: close");
            client.println();
            
            // Relay 1 GPIO control
            if (header.indexOf("GET /1") >= 0) 
            {
              if(digitalRead(relay1)== LOW)
              {
                Serial.println("Relay 1 ON");
                digitalWrite(relay1, HIGH);
                client.print("Relay 1 ON");
              }
              else
              {
                Serial.println("Relay 1 OFF");
                digitalWrite(relay1, LOW);
                client.print("Relay 1 OFF");
              }
            }
 
              // Relay 2 GPIO control
 
              else if (header.indexOf("GET /2") >= 0) 
            {
              if(digitalRead(relay2)== LOW)
              {
                Serial.println("Relay 2 ON");
                digitalWrite(relay2, HIGH);
                client.print("Relay 2 ON");
              }
              else
              {
                Serial.println("Relay 2 OFF");
                
                digitalWrite(relay2, LOW);
                client.print("Relay 2 OFF");
              }
            }
 
              // Relay 3 GPIO control
 
             else if (header.indexOf("GET /3") >= 0) 
            {
              if(digitalRead(relay3)== LOW)
              {
                Serial.println("Relay 3 ON");
                digitalWrite(relay3, HIGH);
                client.print("Relay 3 ON");
              }
              else
              {
                Serial.println("Relay 3 OFF");
                digitalWrite(relay3, LOW);
                client.print("Relay 3 OFF");
              }
            }
 
              // Relay 4 GPIO control
 
              else if (header.indexOf("GET /4") >= 0) 
            {
              if(digitalRead(relay4)== LOW)
              {
                Serial.println("Relay 4 ON");
                digitalWrite(relay4, HIGH);
                client.print("Relay 4 ON");
              }
              else
              {
                Serial.println("Relay 4 OFF");
                digitalWrite(relay4, LOW);
                client.print("Relay 4 OFF");
              } 
            }
 
            // LED GPIO control
 
             else if (header.indexOf("GET /9") >= 0) 
            {
              if(digitalRead(LED)== LOW)
              {
                Serial.println("LED ON");
                
                digitalWrite(LED, HIGH);
                client.print("LED ON");
              }
              else
              {
                Serial.println("LED OFF");
                digitalWrite(LED, LOW);
                client.print("LED OFF");
              } 
            }
            client.stop();
            header = "";
          }
        }
      }    
    }
  }
}

In the HTTP Shortcuts app, from the Basic Request Settings, you’ll choose to GET as the method. The web server URL for turn ON/OFF the Relay will be in this format: `http://youripaddress/1`. You’ll get the IP address on Arduino IDE’s serial monitor, notice these lines in the above code:

...
  // Print local IP address and start web server
  Serial.println("");
  Serial.println("WiFi connected.");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
  server.begin();
}
...

Separately you can control a particular light/fan with your Samsung smartwatch’s BLE (read that guide). These systems will give you enough automation without increasing the burden on your router.