Failed to connect to ESP8266: Timed out waiting for packet header - arduino

Question

I'm using two header file, SoftwareSerial.h and ESP8266WiFi.h. When I compile and upload programs, with ESP8266WiFi.h, it had an error "Failed to connect to ESP8266: Timed out waiting for packet header". I tried it with only ESP8266WiFi.h, but it had an same error. To use this header file, what should I do?
Here's my circuit and code.
#include <ESP8266WiFi.h>
#include <WiFiUdp.h>
const char *ssid = "circuits4you";
const char *pass = "password";
unsigned int localPort = 2000; // local port to listen for UDP packets
IPAddress ServerIP(192,168,4,1);
IPAddress ClientIP(192,168,4,2);
WiFiUDP udp;
char packetBuffer[9]; //Where we get the UDP data
void setup()
{
Serial.begin(9600);
Serial.println();
WiFi.softAP(ssid, pass); //Create Access point
Serial.println("Starting UDP");
udp.begin(localPort);
Serial.print("Local port: ");
Serial.println(udp.localPort());
}
void loop()
{
int cb = udp.parsePacket();
if (!cb)
{
if(Serial.available()>0)
{
udp.beginPacket(ClientIP, 2000);
char a[1];
a[0]=char(Serial.read()); //Serial Byte Read
udp.write(a,1); //Send one byte to ESP8266
udp.endPacket();
}
}
else {
udp.read(packetBuffer, 1);
Serial.print(packetBuffer);
delay(20);
}
}
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Answer 1

Your code is designed for using ESP8266 as a stand-alone microcontroller running with Arduino Core. I realised that you are confusing about the operation modes of ESP8266. There are basically two ways to operate with an ESP8266.
Uses ESP8266 as a stand-alone micropcontroller, in this case, the ESP8266 needs to have the firmware such as RTOS or Arduino Core for ESP8266;
Uses ESP8266 as a plain WiFi device which can be communicate with AT Commands.
Currently your code is designed for running on a stand-alone ESP8266, but I realised that your hardware configuration is configure for communicating with ESP8266 as a WiFi device, and you have the AT command firmware on your ESP8266. In order for Arduino to communicate with ESP8266 via AT Commands, you will need run this Arduino sketch to get started, the sketch basically read the AT command you type in on Serial Monitor and send it to ESP8266, and echo out the msg received from ESP8266:
#include <SoftwareSerial.h>
SoftwareSerial espSerial(2, 3); //RX,TX
// Arduino pin 2 (RX) to ESP8266 TX
// Arduino pin 3 to voltage divider then to ESP8266 RX
// Connect GND from the Arduiono to GND on the ESP8266
// Pull ESP8266 CH_PD HIGH
void setup()
{
Serial.begin(9600); // for communication with the host computer
espSerial.begin(9600); // Soft derail for communicate with ESP8266
// Remember to set 'Both NL & CR' in the serial monitor
}
void loop()
{
// listen for data from the ESP8266 and then write it to the serial monitor
if ( espSerial.available() ) {
Serial.write( espSerial.read() );
}
// listen for manual input from user and send it to the ESP8266
if ( Serial.available() ) {
mySerial.write( Serial.read() );
}
}
Remember to set 'Both NL & CR' in the serial monitor
There is a good official AT Command example from Expressif that you could follow, include UDP communication. You can manually type in the AT Commands via Serial Monitor step by step to test the ESP8266. Once everything works, you could then write the sketch to automate all the AT commands in program to replace the code in the loop().
If communicating with ESP8266 is too much of work and too tedious for you, you might want to consider to use ESP8266 as a stand-alone microcontroller by upgrading your ESP8266 with firmware such as Arduino Core. You can then use the code you shown. But your hardware need to change a little bit in order to set the ESP8266 to firmware flash mode, you need to ground the GPIO0 on ESP8266, and have a reset switch on ESP8266 between reset pin and ground, so that you can press it to put ESP8266 into programming mode.
Please make sure your target board is set to ESP8266 on your Arduino IDE in this case.