Cannot connect to ESP8266 after serial speed change

Question

After some trial and error, tonight my Arduino Uno began talking to an ESP8266 module, with the most common wiring, 3.3V power to the module from a well-sized external supply, direct connection of the 3.3V TX line, and a voltage divider to read from the 5V RX.

SoftwareSerial esp8266(2,3);

void setup()
{
    Serial.begin(9600);
    esp8266.begin(115200);

    char buffer[50];
    esp8266.write("AT\r\n");
    esp8266.readBytes(buffer, sizeof(buffer));
    Serial.println(buffer);

}

After setting the 115200 speed for the ESP8266<->Arduino serial communication, some clear boot messages and command responses appeared on the serial monitor.

Since these messages were interleaved by some garbage characters, I tried reducing the communication speed. For this purpose I issued the command AT+IPR=9600 to the module, which immediately showed some action on the blue LED, an OK response on the console and finally resulted in the same LED being fixed on.

I consequently adjusted the serial speed on the Arduino side, with esp8266.begin(9600);, but could never obtain any further communication with the module. I can now see garbage only at any speed.

Could the module have escalated to a different speed? I tried many of them (4800, 57600, 19200, back to 115200 etc.) but no clear response appeared on the monitor.

May you suggest any attempt to reestablish the connection? Any way to reset the last command result? I'd rather avoid setting up for firmware update, if any simpler solution can be tried.

Answer 1

Here is the solution!

The AT+IPR command was known to break the firmware and make the module unresponsive until a complete reflash.

I found the solution in this forum discussion.