SONOFF - ESP8266 update firmware with Arduino IDE

This is a guide how to upload new firmware using Arduino IDE.
Sonoff is a ESP8266 based WiFi wireless switch that can connect to
appliance of different types and brands. This is a smart switch
to control any device on 110v and 230v.
Note this operation will overwrite the original software, this guide is for people who want to use their own software.

Step 1: Components

SONOFF - WiFi Wireless Smart Switch
PL2303 - USB to UART Converter
USB cable
Several wires
Switch

Step 2: Arduino IDE setup

At the beginning we need the Arduino IDE, If you do not have it
then you can download from this site Arduino IDE download
To be able to program ESP8266 in the Arduino environment, we need
to install the additional platform ESP8266 to the Arduino environment.

Enter <b>http://arduino.esp8266.com/stable/package_esp8266com_index.json</b> into <i>Additional Board Manager URLs</i> field. You can add multiple URLs, separating them with commas. — Enter **http://arduino.esp8266.com/stable/package_esp8266com_index.json** into *Additional Board Manager URLs* field. You can add multiple URLs, separating them with commas.

Open Boards Manager from Tools > Board menu

Select <i>generic ESP8266 module</i> board from Tools > Board menu — Select *generic ESP8266 module* board from Tools > Board menu

Our option settings in In the Arduino IDE should look like this:

Flash Mode: DIO
Flash Frequency: 40MHz
Upload Using: Serial
CPU Frequency: 80MHz
Flash Size: 1M (64K SPIFFS)
Debug Port: Disabled
Debug Level: None
Reset Method: ck
Upload Speed: 115200
Port: Your COM port connected to sonoff

Step 3: Connection of USB converter to ESP8266

PL2303 pin	ESP8266 pin
GND	GND
3.3v	3.3v
RX	TX
TX	RX

Step 4: Flashing a Custom Firmware to SONOFF

Do not connect AC power during the flash cable connection.
To flash the new software to our SONOFF, we have to start Sonoff in flash mode.
Follow this steps process:

Connection of USB converter to SONOFF
Hold down the SONOFF button
Toggle the switch to apply power to the Sonoff circuit
Then, we can release the SONOFF button

After SONOFF is in flash mode, we can upload new software.
This program is very simple, so it is great for first flashing.

#define LED_PIN 13

void setup() {
  Serial.begin(115200);
  Serial.println("START");
  
  pinMode(LED_PIN, OUTPUT);
}
 
void loop() {
  digitalWrite(LED_PIN, HIGH);
  delay(1000);
  digitalWrite(LED_PIN, LOW);
  delay(1000);

  Serial.println("LED");
}

This is a common problem, if you happen to do it then try it once.

If everything goes well, the message will be as above and LED will be blinking.