Wireless Communication using NodeMCUs as Transmitter and Receiver: A DIY Project

#include <ESP8266WiFi.h>

const int trigPin = 12;   //d6
const int echoPin = 14;   //d5
const int ledPin = 2;     //d4

//define sound velocity in cm/uS
#define SOUND_VELOCITY 0.034
#define CM_TO_INCH 0.393701

const char *ssid      = "Sempai";
const char *password  = "watchanime";

float distanceCm;
int sensorValue0 = 0;
int sensorValue1 = 0;
int sensorValue2 = 0;
int sensorValue3 = 0;

void setup() {
  Serial.begin(115200);
  delay(10);

  pinMode(ledPin, OUTPUT);
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
  pinMode(echoPin, INPUT); // Sets the echoPin as an Input

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

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

}

void loop() {
  // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Reads the echoPin, returns the sound wave travel time in microseconds
  long duration = pulseIn(echoPin, HIGH);
  
  // Calculate the distance
  distanceCm = duration * SOUND_VELOCITY/2;
  
  // Convert to inches
  float distanceInch = distanceCm * CM_TO_INCH;
  
  // Check if distance is 10cm
  if(distanceCm <= 10) {
    digitalWrite(ledPin, LOW); // turn off LED
    sensorValue0 = 0;
  } else {
    delay(5000);
    digitalWrite(ledPin, HIGH); // turn on LED
    sensorValue0 = 1;

  }

  // Use WiFiClient class to create TCP connections
  WiFiClient client;
  const char * host = "192.168.4.1";            //default IP address
  const int httpPort = 80;

  if (!client.connect(host, httpPort)) {
    Serial.println("connection failed");
    return;
  }

  // We now create a URI for the request. Something like /data/?sensor_reading=123
  String url = "/data/";
  url += "?sensor_reading=";
  url +=  "{\"sensor0_reading\":\"sensor0_value\",\"sensor1_reading\":\"sensor1_value\",\"sensor2_reading\":\"sensor2_value\",\"sensor3_reading\":\"sensor3_value\"}";

  url.replace("sensor0_value", String(sensorValue0));
  url.replace("sensor1_value", String(sensorValue1));
  url.replace("sensor2_value", String(sensorValue2));
  url.replace("sensor3_value", String(sensorValue3));

  // This will send the request to the server
  client.print(String("GET ") + url + " HTTP/1.1\r\n" +
               "Host: " + host + "\r\n" +
               "Connection: close\r\n\r\n");
  unsigned long timeout = millis();
  while (client.available() == 0) {
    if (millis() - timeout > 5000) {
      Serial.println(">>> Client Timeout !");
      client.stop();
      return;
    }
  }
}

This is a sketch of an ESP8266 microcontroller that is connected to a relay module. The code receives sensor readings via an HTTP GET request to the server's "/data/" endpoint. It then deserializes the received JSON data to extract four sensor readings and stores them in the sensorValue0, sensorValue1, sensorValue2, and sensorValue3 variables.

The toggle_relays() function checks the values of the four sensor readings and turns the relay on or off accordingly. If a sensor reading is 0, the relay is turned off, and if it's 1, the relay is turned on. The relay is connected to the relayPin pin, which is set to output mode in the setup() function.

The code also sets up an access point with the SSID "Sempai" and password "watchanime" using the WiFi.softAP() function. It then listens for HTTP requests on port 80 using the server.begin() function and responds to requests to the "/data/" endpoint by calling the handleSentVar() function.

Overall, the code seems to be designed to receive sensor readings and control a relay based on those readings. However, there is no information provided on the sensor types, how they are connected to the ESP8266, or how the readings are being transmitted to the server.

# CODE : 

In conclusion, using NodeMCUs as a transmitter and receivers can be a useful and cost-effective way to communicate between two devices wirelessly. With the help of the ESP8266WiFi library and ArduinoJson library, it is easy to set up a web server on the transmitter NodeMCU that can send data to the receiver NodeMCU through an HTTP GET request. The receiver NodeMCU can then process the data and take appropriate actions based on the received information.

There are many potential applications for this project, such as home automation, remote control of devices, and monitoring systems. With some modifications and additions, this project can be expanded to include more sensors, actuators, and features, making it even more versatile and useful. Overall, using NodeMCUs as a transmitter and receivers provides an accessible and flexible way to create wireless communication systems.