ESP01 - Introduction

Pin configuration of the ESP01 is shown below:

Connection of ESP01 to the Arduino:

ESP01	Arduino
TX	Pin 3
CH_PD	3.3V
RST	No Connection
VCC	3.3V
RX	Pin 4*
GPIO0	No Connection
GPIO2	No Connection
GND	GND

* A resistor network to be used to drop the 5V signal from the Arduino to 3.3V for the ESP01.

A typical Arduino sketch to communicate with the ESP01:

#include <SoftwareSerial.h>

#define DEBUG true

// UNO's D3 connected to ESP's TX
// UNO's D4 connected to ESP's RX via resistor network
SoftwareSerial ESP01(3, 4); // RX, TX

String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;  // whether the string is complete

void setup() {                  
  Serial.begin(9600); 
  while (!Serial);
  Serial.println("Starting...");
  ESP01.begin(9600);
  inputString.reserve(200); // reserve 200 bytes for the inputString:
}

void loop() {
  if (stringComplete) {
    sendData(inputString,2000,DEBUG);  // print the string when a newline arrives:
    inputString = "";   // clear the string:
    stringComplete = false;
  }
  delay(100);
}

void serialEvent() {
  while (Serial.available()) {      
    char inChar = (char)Serial.read();      // get the new byte:
    
    inputString += inChar;                  // add it to the inputString:
    // if the incoming character is a newline, set a flag
    // so the main loop can do something about it:
    if (inChar == '\n') {
      stringComplete = true;
    }
  }
}

String sendData(String command, const int timeout, boolean debug)
{
    String response = "";
    ESP01.print(command);
    long int time = millis();
    while( (time+timeout) > millis())
    {
      while(ESP01.available())
      {
        // "Construct" response from ESP01 as follows - this is to be displayed on Serial Monitor. 
        char c = ESP01.read(); // read the next character.
        response+=c;
      }  
    }
    if(debug) Serial.print(response);
    return (response);
}