ESP8266 AT Commands Tutorial with Arduino

In this tutorial, we are going to explore the pre-installed AT firmware inside the ESP8266.

Table Of Contents

The AT Firmware
Code
Code Explanation
Demonstration

The AT Firmware

The AT firmware is a pre-installed software in the ESP8266’s ROM (Read-Only Memory). It uses AT commands which are based on the Hayes Command Set. The Hayes Commands Set are commands for telecommunication operations. For instance, dialing a number or making a call.

Further, AT commands are often used for rapid testing of the ESP8266. They can either be sent using the serial monitor or via the ESP8266 sketch.

Sending AT commands using Arduino UNO

Parts you need:

Arduino UNO
ESP8266-01 module
1 x 1k? resistor
1 x 2.2k? resistor
1 x 10k? resistor
Jumper wires

First, create a voltage divider using a 1k? and 2.2k? resistor. The default logic level of an Arduino is 5V. Although the ESP8266-01’s TX and RX pin are 5V tolerant, it still gets damage in the long run. To prevent this, we use a logic level converter or a voltage divider to reduce the signal to 3.3V. Next, initialize the ESP-01. Connect the EN/CH-PD (Enable) pin to the 3.3V supply. Use a 10k pull-up resistor.

In the Arduino IDE, choose Generic ESP8266 Module as your board of choice.

Open the serial monitor. Set the baud rate to 115200 and enter the desired AT command.

Fundamental AT commands

AT+CWMODE

As mentioned in the previous article, the ESP8266 can be set to 3 different modes. To set the module as a station, enter AT+CWMODE=1. To set as an access point, enter AT+CWMODE=2. As both, enter AT+CWMODE=3. To check the current mode the ESP8266 is in, use AT+CWMODE?.

AT+CWLAP

See the available WiFi networks in your location.

AT+CWJAP="WiFi network name","Wifi network password"

Connect to a WiFi network.

AT+CIFSR

See ESP-01’s MAC and IP address.

AT+CIPMUX

Enable multiple connections using AT+CIPMUX=1. Disable it by using AT+CIPMUX=0.

AT+CIPSERVER

Start a server using AT+CIPSERVER=1,80. The first number indicates status. A value of 0 means closed while 1 means opened. The second number tells the port number.

AT+CIPSEND

Sends data to your server. To demonstrate, suppose you want to send 5 characters to channel 0. You should enter AT+CIPSEND=0,5 in the serial monitor.

The commands should look like this in the serial monitor.

They are certainly easier to implement in the serial monitor than your usual Arduino framework.

See all 88 AT commands here.

ESP8266 AT Commands

But they have their limits. Let’s use them on actual Arduino code in the next section.

Using the Arduino to program the ESP-01

Parts you need:

Arduino UNO
ESP8266-01 module
1 x 1k? resistor
1 x 2.2k? resistor
1 x 10k? resistor
Jumper wires

First, to set the Arduino board as an ESP programmer, connect the RESET pin to GROUND. Then, create a voltage divider just like before. Next, initialize the ESP-01. Connect the EN/CH-PD (Enable) pin to the 3.3V supply. Use a 10k pull-up resistor as well. Finally. connect the pin 0 to GND to start program mode.

In the Arduino IDE, choose Generic ESP8266 Module.

Using the NodeMCU

Parts you need:

NodeMCU development board

Plug and play! All you need to do is set the board in the Arduino IDE to NodeMCU.

Code


#include <SoftwareSerial.h> SoftwareSerial esp8266(2,3); #define serialCommunicationSpeed 115200 #define DEBUG true void setup() { Serial.begin(serialCommunicationSpeed); esp8266.begin(serialCommunicationSpeed); InitWifiModule(); } void loop() { if(esp8266.available()) { if(esp8266.find("+IPD,")) { delay(1000); int connectionId = esp8266.read()-48; String webpage = "<h1>Hello World!</h1>"; String cipSend = "AT+CIPSEND="; cipSend += connectionId; cipSend += ","; cipSend +=webpage.length(); cipSend +="rn"; sendData(cipSend,1000,DEBUG); sendData(webpage,1000,DEBUG); String closeCommand = "AT+CIPCLOSE="; closeCommand+=connectionId; // append connection id closeCommand+="rn"; sendData(closeCommand,3000,DEBUG); } }
} String sendData(String command, const int timeout, boolean debug)
{ String response = ""; esp8266.print(command); long int time = millis(); while( (time+timeout) > millis()) { while(esp8266.available()) { char c = esp8266.read(); response+=c; } } if(debug) { Serial.print(response); } return response; } void InitWifiModule()
{ sendData("AT+RSTrn", 2000, DEBUG); sendData("AT+CWJAP="SSID","Password"rn", 2000, DEBUG); delay (3000); sendData("AT+CWMODE=1rn", 1500, DEBUG); delay (1500); sendData("AT+CIFSRrn", 1500, DEBUG); delay (1500); sendData("AT+CIPMUX=1rn", 1500, DEBUG); delay (1500); sendData("AT+CIPSERVER=1,80rn", 1500, DEBUG); }

Code Explanation

First, initialize a SoftwareSerial communication line. The default pins for serial communication, 0 and 1, tend to get busy when the serial monitor is running. To avoid having corrupted data, we transfer serial communication with the ESP-01 to pins 2 and 3.

#include <SoftwareSerial.h> SoftwareSerial esp8266(2,3);

Then, in the setup section, initialize the serial monitor and serial communications with your ESP8266’s baud rate. The default baud rate is 115200. Using InitWifiModule(), connect to your WiFi network.

void setup() { Serial.begin(serialCommunicationSpeed); esp8266.begin(serialCommunicationSpeed); InitWifiModule(); }

Then, in the loop section, we store AT commands in strings so that we can send them via Software Serial. We use the sendData() to send them.

void loop() { if(esp8266.available()) { if(esp8266.find("+IPD,")) { delay(1000); int connectionId = esp8266.read()-48; String webpage = "<h1>Hello World!</h1>"; String cipSend = "AT+CIPSEND="; cipSend += connectionId; cipSend += ","; cipSend +=webpage.length(); cipSend +="rn"; sendData(cipSend,1000,DEBUG); sendData(webpage,1000,DEBUG); String closeCommand = "AT+CIPCLOSE="; closeCommand+=connectionId; closeCommand+="rn"; sendData(closeCommand,3000,DEBUG); } }
}

Demonstration

Upload the sketch to your ESP8266. Next, check for the serial monitor. It should display the IP address of your local webserver. Enter the IP address to your favorite browser.

[faq] [faq_q]What are AT commands on the ESP8266?[/faq_q] [faq_a]AT commands are short text commands you send over UART to instruct the ESP8266 to do things like join Wi-Fi, send TCP/UDP data, or query its state. They’re the original interface for treating the ESP8266 as a Wi-Fi modem alongside an Arduino or another microcontroller.[/faq_a][faq_q]What baud rate does the ESP8266 AT firmware use by default?[/faq_q] [faq_a]Most factory firmwares default to 115200 baud. Older firmware versions sometimes default to 9600. If AT echoes garbage, try 9600 first, then 115200, then 57600 — set with AT+UART_DEF=115200,8,1,0,0.[/faq_a][faq_q]How do I check if my ESP8266 firmware supports AT commands?[/faq_q] [faq_a]Send AT followed by carriage return + linefeed. If the chip replies OK, you have AT firmware. If it boots into a custom sketch, it doesn’t — you’ll need to flash AT firmware (Espressif provides ESP8266 NonOS AT/SDK images).[/faq_a][faq_q]Can I update the ESP8266 AT firmware over USB without a special programmer?[/faq_q] [faq_a]Yes, with a USB-to-serial adapter (CP2102, CH340) and the ESP8266 in flash mode (GPIO 0 to GND, reset). esptool.py erase_flash followed by esptool.py write_flash 0x0 ai-thinker-firmware.bin works on most ESP8266 modules.[/faq_a][/faq]

Frequently Asked Questions

What does this Using AT commands on the ESP8266 tutorial cover?

In this tutorial, we are going to explore the pre-installed AT firmware inside the ESP8266.

Can I use an Arduino Nano or Mega instead of UNO for the Using AT commands on the ESP8266 build?

Yes. Nano shares the same ATmega328P and pinout. Mega has more I/O if you outgrow UNO. The code stays the same — just match the pin numbers used in the Sample Code section.

Why does my Using AT commands on the ESP8266 sketch fail to upload?

Usually wrong COM port, missing CH340/CH341 driver for clone boards, or another program holding the serial port. Disconnect the board, install the driver, reselect the port, retry.