This project brings support for ESP8266 chip to the Arduino environment. ESP8266WiFi library bundled with this project has the same interface as the WiFi Shield library, making it easy to re-use existing code and libraries.

Installing with Boards Manager

Starting with 1.6.4, Arduino allows installation of third-party platform packages using Boards Manager. We have packages available for Windows, Mac OS, and Linux (32 and 64 bit).

  • Install Arduino 1.6.4 from the Arduino website.
  • Start Arduino and open Perferences window.
  • Enter into Additional Board Manager URLs field. You can add multiple URLs, separating them with commas.
  • Open Boards Manager from Tools > Board menu and install esp8266 platform (and don’t forget to select your ESP8266 board from Tools > Board menu after installation).

Change log

Building latest version from source

$ git clone
$ cd Arduino/build
$ ant dist

Supported boards

  • Generic esp8266 modules (without auto-reset support)
  • NodeMCU
  • Olimex MOD-WIFI-ESP8266

Things that work

Basic Wiring functions

pinMode, digitalRead, digitalWrite, analogWrite work as usual.

Pin numbers correspond directly to the esp8266 GPIO pin numbers. To read GPIO2, call digitalRead(2);


analogRead(A0) reads the value of the ADC channel connected to the TOUT pin.

analogWrite(pin, value) enables software PWM on the given pin. PWM may be used on pins 0 to 15. Call analogWrite(pin, 0) to disable PWM on the pin. value may be in range from 0 to PWMRANGE, which is currently equal to 1023.

Pin interrupts are supported through attachInterrupt, detachInterrupt functions. Interrupts may be attached to any GPIO pin, except GPIO16. Standard Arduino interrupt types are supported: CHANGE, RISING, FALLING.

Pin Functions

The most usable pin functions are mapped to the macro SPECIAL, so calling pinMode(pin, SPECIAL) will switch that pin in the most usable FUNCTION_X. Those are UART RX/TX on pins 1 – 3, HSPI for pins 12-15 and CLK functions for pins 0, 4 and 5.

Timing and delays

millis and micros return the number of milliseconds and microseconds elapsed after reset, respectively.

delay pauses the sketch for a given number of milliseconds and allows WiFi and TCP/IP tasks to run. delayMicroseconds pauses for a given number of microseconds.

Remember that there is a lot of code that needs to run on the chip besides the sketch when WiFi is connected. WiFi and TCP/IP libraries get a chance to handle any pending events each time the loop() function completes, OR when delay(...) is called. If you have a loop somewhere in your sketch that takes a lot of time (>50ms) without calling delay(), you might consider adding a call to delay function to keep the WiFi stack running smoothly.

There is also a yield() function which is equivalent to delay(0). The delayMicroseconds function, on the other hand, does not yield to other tasks, so using it for delays more than 20 milliseconds is not recommended.


Serial object works much the same way as on a regular Arduino. Apart from hardware FIFO (128 bytes for TX and RX) HardwareSerial has additional 256-byte TX and RX buffers. Both transmit and receive is interrupt-driven. Write and read functions only block the sketch execution when the respective FIFO/buffers are full/empty.

Serial uses UART0, which is mapped to pins GPIO1 (TX) and GPIO3 (RX). Serial may be remapped to GPIO15 (TX) and GPIO13 (RX) by calling Serial.swap(); after Serial.begin();. Calling swap again maps UART0 back to GPIO1 and GPIO3.

Serial1 uses UART1 which is a transmit-only UART. UART1 TX pin is GPIO2. To use Serial1, call Serial1.begin.

By default the diagnostic output from WiFi libraries is disabled when you call Serial.begin. To enable debug output again, call Serial.setDebugOutput(true);. To redirect debug output to Serial1 instead, call Serial1.setDebugOutput(true);.

Both Serial and Serial1 objects support 5, 6, 7, 8 data bits, odd (O), even (E), and no (N) parity, and 1 or 2 stop bits. To set the desired mode, call Serial.begin(baudrate, SERIAL_8N1);, Serial.begin(baudrate, SERIAL_6E2);, etc.


The Program memory features work much the same way as on a regular Arduino; placing read only data and strings in read only memory and freeing heap for your application. The important difference is that on the esp8266 the literal strings are not pooled. This means that the same literal string defined inside a F("") and/or PSTR("") will take up space for each instance in the code. So you will need to manage the duplicate strings yourself.

WiFi(ESP8266WiFi library)

This is mostly similar to WiFi shield library. Differences include:

  • WiFi.mode(m): set mode to WIFI_AP, WIFI_STA, or WIFI_AP_STA.
  • call WiFi.softAP(ssid) to set up an open network
  • call WiFi.softAP(ssid, password) to set up a WPA2-PSK network (password should be at least 8 characters)
  • WiFi.macAddress(mac) is for STA, WiFi.softAPmacAddress(mac) is for AP.
  • WiFi.localIP() is for STA, WiFi.softAPIP() is for AP.
  • WiFi.RSSI() doesn’t work
  • WiFi.printDiag(Serial); will print out some diagnostic info
  • WiFiUDP class supports sending and receiving multicast packets on STA interface. When sending a multicast packet, replace udp.beginPacket(addr, port) with udp.beginPacketMulticast(addr, port, WiFi.localIP()). When listening to multicast packets, replace udp.begin(port) with udp.beginMulticast(WiFi.localIP(), multicast_ip_addr, port). You can use udp.destinationIP() to tell whether the packet received was sent to the multicast or unicast address. Also note that multicast doesn’t work on softAP interface.

WiFiServer, WiFiClient, and WiFiUDP behave mostly the same way as with WiFi shield library. Four samples are provided for this library. You can see more commands here:


Library for calling functions repeatedly with a certain period. Two examples included.

It is currently not recommended to do blocking IO operations (network, serial, file) from Ticker callback functions. Instead, set a flag inside the ticker callback and check for that flag inside the loop function.


This is a bit different from standard EEPROM class. You need to call EEPROM.begin(size) before you start reading or writing, size being the number of bytes you want to use. Size can be anywhere between 4 and 4096 bytes.

EEPROM.write does not write to flash immediately, instead you must call EEPROM.commit() whenever you wish to save changes to flash. EEPROM.end() will also commit, and will release the RAM copy of EEPROM contents.

EEPROM library uses one sector of flash located at 0x7b000 for storage.

Three examples included.

I2C (Wire library)

Wire library currently supports master mode up to approximately 450KHz. Before using I2C, pins for SDA and SCL need to be set by calling Wire.begin(int sda, int scl), i.e. Wire.begin(0, 2); on ESP-01, else they default to pins 4(SDA) and 5(SCL).


SPI library supports the entire Arduino SPI API including transactions, including setting phase (CPHA). Setting the Clock polarity (CPOL) is not supported, yet (SPI_MODE2 and SPI_MODE3 not working).

ESP-specific APIs

APIs related to deep sleep and watchdog timer are available in the ESP object, only available in Alpha version.

ESP.deepSleep(microseconds, mode) will put the chip into deep sleep. mode is one of WAKE_RF_DEFAULT, WAKE_RFCAL, WAKE_NO_RFCAL, WAKE_RF_DISABLED. (GPIO16 needs to be tied to RST to wake from deepSleep.)

ESP.wdtEnable(), ESP.wdtDisable(), and ESP.wdtFeed() provide some control over the watchdog timer.

ESP.reset() resets the CPU.

ESP.getFreeHeap() returns the free heap size.

ESP.getChipId() returns the ESP8266 chip ID as a 32-bit integer.

Several APIs may be used to get flash chip info:

ESP.getFlashChipId() returns the flash chip ID as a 32-bit integer.

ESP.getFlashChipSize() returns the flash chip size, in bytes, as seen by the SDK (may be less than actual size).

ESP.getFlashChipSpeed(void) returns the flash chip frequency, in Hz.

ESP.getCycleCount() returns the cpu instruction cycle count since start as an unsigned 32-bit. This is useful for accurate timing of very short actions like bit banging.

OneWire (from

Library was adapted to work with ESP8266 by including register definitions into OneWire.h Note that if you already have OneWire library in your Arduino/libraries folder, it will be used instead of the one that comes with this package.

mDNS responder (ESP8266mDNS library)

Allows the sketch to respond to multicast DNS queries for domain names like “foo.local”. Currently the library only works on STA interface, AP interface is not supported. See attached example and library README file for details.

Other libraries (not included with the IDE)

Libraries that don’t rely on low-level access to AVR registers should work well. Here are a few libraries that were verified to work:

Upload via serial port

Pick the correct serial port. You need to put ESP8266 into bootloader mode before uploading code.

Minimal hardware Setup for Bootloading and usage

ESPxx Hardware

PIN Resistor Serial Adapter
VCC VCC (3.3V)
Reset* RTS
GPIO15* PullDown
CH_PD PullUp
  • GPIO15 is also named MTDO
  • Reset is also named RSBT or REST (adding PullUp improves the stability of the Module)
  • GPIO2 is alternative TX for the boot loader mode

ESP01 example:

Minimal hardware Setup for Bootloading only

ESPxx Hardware

PIN Resistor Serial Adapter
VCC VCC (3.3V)
Reset RTS*
GPIO15 PullDown
CH_PD PullUp
  • Note
    • if no RTS is used a manual power toggle is needed

Issues and support


Submit issues on Github:

License and credits

Arduino IDE is based on Wiring and Processing. It is developed and maintained by the Arduino team. The IDE is licensed under GPL, and the core libraries are licensed under LGPL.

This build includes an xtensa gcc toolchain, which is also under GPL.

Espressif SDK included in this build is under Espressif Public License.

Esptool written by Christian Klippel is licensed under GPLv2, currently maintained by Ivan Grokhotkov:

ESP8266 core support, ESP8266WiFi, Ticker, ESP8266WebServer libraries were written by Ivan Grokhotkov, [email protected].

SPI Flash File System (SPIFFS) written by Peter Andersson is used in this project. It is distributed under MIT license.