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ESP-01 module by AI-Thinker
Manufacturer Espressif
Type Microcontroller
CPU @ 80 MHz (default) or 160 MHz
Memory 64 KiB instruction, 96 KiB data
Input 16 GPIO pins
Power 3.3 VDC

The ESP8266 is a low-cost Wi-Fi chip with full TCP/IP stack and MCU (microcontroller unit) capability produced by Shanghai-based Chinese manufacturer, Espressif Systems.[1]

The chip first came to the attention of western makers in August 2014 with the ESP-01 module, made by a third-party manufacturer, AI-Thinker. This small module allows microcontrollers to connect to a Wi-Fi network and make simple TCP/IP connections using Hayes-style commands. However, at the time there was almost no English-language documentation on the chip and the commands it accepted.[2] The very low price and the fact that there were very few external components on the module which suggested that it could eventually be very inexpensive in volume, attracted many hackers to explore the module, chip, and the software on it, as well as to translate the Chinese documentation.[3]

The ESP8285 is an ESP8266 with 1 MiB of built-in flash, allowing for single-chip devices capable of connecting to Wi-Fi.[4]

The successor to these microcontroller chips is the ESP32.


ESP-01 wireframe.
  • Processor: L106 32-bit RISC microprocessor core based on the Tensilica Xtensa Diamond Standard 106Micro running at 80 MHz*
  • 64 KiB of instruction RAM, 96 KiB of data RAM
  • External QSPI flash: 512 KiB to 4 MiB* (up to 16 MiB is supported)
  • IEEE 802.11 b/g/n Wi-Fi
  • 16 GPIO pins
  • SPI
  • I²C
  • I²S interfaces with DMA (sharing pins with GPIO)
  • UART on dedicated pins, plus a transmit-only UART can be enabled on GPIO2
  • 10-bit ADC (this is a Successive Approximation ADC)

* Both the CPU and flash clock speeds can be doubled by overclocking on some devices. CPU can be run at 160 MHz and flash can be sped up from 40 MHz to 80 MHz.[citation needed] Success varies chip to chip.[citation needed]


In late October 2014, Espressif released a software development kit (SDK) that allowed the chip to be programmed, removing the need for a separate microcontroller.[5] Since then, there have been many official SDK releases from Espressif; Espressif maintains two versions of the SDK — one that is based on FreeRTOS and the other based on callbacks.[6]

An alternative to Espressif's official SDK is the open source ESP-Open-SDK[7] that is based on the GCC toolchain. ESP8266 uses the Cadence Tensilica L106 microcontroller and the GCC toolchain is open-sourced and maintained by Max Filippov.[8] Another alternative is the "Unofficial Development Kit" by Mikhail Grigorev.[9][10]

Open source SDKs include:

  • NodeMCU — A Lua-based firmware.
  • Arduino — A C++ based firmware. This core enables the ESP8266 CPU and its Wi-Fi components to be programmed like any other Arduino device. The ESP8266 Arduino Core is available through GitHub.
  • MicroPython — A port of MicroPython (an implementation of Python for embedded devices) to the ESP8266 platform.
  • ESP8266 BASIC — An open source basic interpreter specifically tailored for the internet of things. Self hosting browser based development environment.
  • Zbasic for ESP8266 — A subset of Microsoft's widely used Visual Basic 6 which has been adapted as a control language for the ZX microcontroller family and the ESP8266.
  • Espruino — An actively maintained JavaScript SDK and firmware, closely emulating Node.js. Supports a few MCUs, including the ESP8266.
  • Mongoose Firmware — An open source firmware with complimentary cloud service.[11]
  • ESP-Open-SDK — Free and open (as much as possible) integrated SDK for ESP8266/ESP8285 chips.
  • ESP-Open-RTOS — Open source FreeRTOS-based ESP8266 software framework.

Espressif modules[edit]

This is the series of ESP8266-based modules made by Espressif.

Name Active pins Pitch Form factor LEDs Antenna Shielded? Dimensions (mm) Notes
ESP-WROOM-02[12] 18 0.1 in 2×9 DIL No PCB trace Yes 18 × 20 FCC ID 2AC7Z-ESPWROOM02

In the table above (and the two tables which follow), "Active pins" include the GPIO and ADC pins with which you can attach external devices to the ESP8266 MCU. The "Pitch" is the space between pins on the ESP8266 module, which is important to know if you are going to breadboard the device. The "Form factor" also describes the module packaging as "2 × 9 DIL", meaning two rows of 9 pins arranged "Dual In Line", like the pins of DIP ICs. Many ESP-xx modules include a small on-board LED which can be programmed to blink and thereby indicate activity. There are several antenna options for ESP-xx boards including a trace antenna, an on-board ceramic antenna, and an external connector which allows you to attach an external Wi-Fi antenna. Since Wi-Fi communications generates a lot of RFI (Radio Frequency Interference), governmental bodies like the FCC like shielded electronics to minimize interference with other devices. Some of the ESP-xx modules come housed within a metal box with an FCC seal of approval stamped on it. First and second world markets will likely demand FCC approval and shielded Wi-Fi devices.

AI-Thinker modules[edit]

ESP-01 module
AI-Thinker ESP8266 modules (ESP-12F, black color) soldered to breakout boards (white color)

These are the first series of modules made with the ESP8266 by the third-party manufacturer AI-Thinker and remain the most widely available.[13] They are collectively referred to as "ESP-xx modules". To form a workable development system they require additional components, especially a serial TTL-to-USB adapter (sometimes called a USB-to-UART bridge) and an external 3.3 volt power supply. Novice ESP8266 developers are encouraged to consider larger ESP8266 Wi-Fi development boards like the NodeMCU which includes the USB-to-UART bridge and a Micro-USB connector coupled with a 3.3 volt power regulator already built into the board. When project development is complete, these components are not needed anymore and it can be considered using these cheaper ESP-xx modules as a lower power, smaller footprint option for production runs.

Name Active pins Pitch Form factor LEDs Antenna Shielded? Dimensions (mm) Notes
ESP-01 6 0.1 in 2×4 DIL Yes PCB trace No 14.3 × 24.8
ESP-02 6 0.1 in 2×4 castellated No U.FL connector No 14.2 × 14.2
ESP-03 10 2 mm 2×7 castellated No Ceramic No 17.3 × 12.1
ESP-04 10 2 mm 2×4 castellated No None No 14.7 × 12.1
ESP-05 3 0.1 in 1×5 SIL No U.FL connector No 14.2 × 14.2
ESP-06 11 misc 4×3 dice No None Yes 14.2 × 14.7 Not FCC approved
ESP-07 14 2 mm 2×8 pinhole Yes Ceramic + U.FL connector Yes 20.0 × 16.0 Not FCC approved
ESP-07S 14 2 mm 2×8 pinhole No U.FL connector Yes 17.0 × 16.0 FCC and CE approved
ESP-08 10 2 mm 2×7 castellated No None Yes 17.0 × 16.0 Not FCC approved
ESP-09 10 misc 4×3 dice No None No 10.0 × 10.0
ESP-10 3 2 mm? 1×5 castellated No None No 14.2 × 10.0
ESP-11 6 0.05  1×8 pinhole No Ceramic No 17.3 × 12.1
ESP-12 14 2 mm 2×8 castellated Yes PCB trace Yes 24.0 × 16.0 FCC and CE approved[14]
ESP-12E 20 2 mm 2×8 castellated Yes PCB trace Yes 24.0 × 16.0 4 MiB Flash
ESP-12F 20 2 mm 2×8 castellated Yes PCB trace Yes 24.0 × 16.0 FCC and CE approved. Improved antenna performance. 4 MiB Flash
ESP-12S 14 2 mm 2×8 castellated Yes PCB trace Yes 24.0 × 16.0 4 MiB Flash. FCC approved[15]
ESP-13 16 1.5 mm 2×9 castellated No PCB trace Yes W18.0 × L20.0 Marked as ″FCC″. Shielded module is placed sideways, as compared to the ESP-12 modules.
ESP-14 22 2 mm 2×8 castellated +6 No PCB trace Yes 24.3 × 16.2

Other boards[edit]

The popularity of many of these "other boards" over the earlier ESP-xx modules is the inclusion of an on-board USB-to-UART bridge (like the Silicon Labs' CP2102 or the WCH CH340G) and a Micro-USB connector coupled with a 3.3 volt regulator to provide both power to the board and connectivity to the host (software development) computer commonly referred to as the console. With earlier ESP-xx modules, these two items (the USB-to-Serial adaptor and a 3.3 volt regulator) had to be purchased separately and be wired into the ESP-xx circuit. Modern ESP8266 boards like the NodeMCU boards are a lot less painful and offer more GPIO pins to play with. Most of these "other boards" are based on the ESP-12E module, but new modules are being introduced seemingly every few months.

Name Active pins Pitch Form factor LEDs Antenna Shielded? Dimensions (mm) Notes
Bolt IoT 14 0.1 in 2×14 DIL Yes PCB trace Yes 30 × 40 Comes with an on Board SD card and technologies like Lib-Discovery and Fail Safe Mode. Has its own cloud for IoT.
Olimex MOD-WIFI-ESP8266[16] 2 0.1 in UEXT module Yes PCB trace No ? Only RX/TX are connected to UEXT connector
Olimex MOD-WIFI-ESP8266-DEV[17] 20 0.1 in 2×11 DIL + castellated Yes PCB trace No 33 × 23 All available GPIO pins are connected, also has pads for soldering UEXT connector (with RX/TX and SDA/SCL signals)
NodeMCU DEVKIT 14 0.1 in 2×15 DIL Yes PCB trace Yes 49 × 24.5 Uses the ESP-12 module, includes USB serial interface
Adafruit Huzzah ESP8266 breakout[18] 14 0.1 in 2×10 DIL Yes PCB trace Yes 25 × 38 Uses the ESP-12 module
SparkFun ESP8266 Thing[19] WRL-13231 12 0.1 in 2×10 DIL Yes PCB trace + U.FL socket No 58 × 26 FTDI serial header, Micro-USB socket for power, includes Li-ion battery charger
KNEWRON Technologies smartWIFI[20] 12 0.1 in 2×20 DIL Yes 1 RGB PCB trace Yes 25.4 × 50.8 CP2102 USB bridge, includes battery charger, micro-USB socket for power and battery charging, 1 RGB LED and USER / Reflash button
WeMos[21] D1[22] 12 0.1 in Arduino Uno Yes PCB trace Yes 53.4 × 68.6 Uses the ESP-12F module, Micro-USB socket, discontinued in favor of WeMos D1 R2
WeMos[21] D1 R2[23] 12 0.1 in Arduino Uno Yes PCB trace Yes 53.4 × 68.6 Uses the ESP-12F module, Micro-USB socket
WeMos[21] D1 mini[24] 12 0.1 in 2×8 DIL Yes PCB trace Yes 25.6 × 34.2 Uses the ESP-12S module, Micro-USB socket
WeMos[21] D1 mini Lite[25] 12 0.1 in 2×8 DIL Yes PCB trace Yes 25.6 × 34.2 Based on the ESP8285, an ESP8266 with 1 MiB flash built-in; Micro-USB socket
WeMos[21] D1 mini Pro[26] 12 0.1 in 2×8 DIL Yes Ceramic and U.FL socket Yes 25.6 × 34.2 Uses the ESP8266EX module, Micro-USB socket, U.FL antenna connector, 16 MiB flash
ESPert ESPresso Lite[27] 16 0.1 in 2×8 DIL Yes PCB trace Yes 26.5 × 57.6 Uses the WROOM-02 module. Produced in limited quantity as beta version.
ESPert ESPresso Lite V2.0[28] 24 0.1 in 2×10 DIL Yes PCB trace Yes 28 × 61 Improved design and feature to ESPresso Lite.
In-Circuit ESP-ADC[29] 18 0.1 in 2×9 DIL No U.FL socket No 22.9 × 14.9 Uses the ESP8266EX
Watterott ESP-WROOM02-Breakout[30] 14 0.1 in 2×10 DIL Yes PCB trace Yes 40.64 × 27.94 Uses the Espressif ESP-WROOM-02 module.
Geek wave solution IOT_WROOM-02 based WIFI development board 20 0.1 in ? Yes PCB trace Yes 93.80 × 80.02 ESP8266 WROOM-02

See also[edit]


  1. ^ Linux and Open Source Hardware for IoT
  2. ^ Brian Benchoff (August 26, 2014). "New Chip Alert: The ESP8266 WiFi Module (It’s $5)". hackaday. Retrieved 2015-06-24. 
  3. ^ Brian Benchoff (September 6, 2014). "The Current State of ESP8266 Development". hackaday. Retrieved 2015-06-24. 
  4. ^ "Espressif Announces ESP8285 Wi-Fi Chip for Wearable Devices". Espressif. Mar 9, 2016. Retrieved 2016-07-10. 
  5. ^ Brian Benchoff (October 25, 2014). "An SDK for the ESP8266 WiFi Chip". hackaday. Retrieved 2015-06-24. 
  6. ^ Espressif Systems (July 29, 2015). "Official SDK release from Espressif for ESP8266". Espressif. Retrieved 2015-08-08. 
  7. ^
  8. ^ Max Filippov (Feb 15, 2015). "ESP8266 GCC Toolchain". Retrieved 2015-08-08. 
  9. ^>
  10. ^
  11. ^
  12. ^ "Espressif ESP-WROOM-02". Espressif Inc. Retrieved 2015-07-29. 
  13. ^ "ESP8266 module family". wiki. Retrieved 2015-06-24. 
  14. ^ "2ADUIESP-12 by Shenzhen Anxinke technology co., LTD for Wi-Fi Module". FCC. December 30, 2014. Retrieved 2015-06-24. 
  15. ^ "FCC ID 2AHMR-ESP12S, Shenzhen Ai-Thinker Technology co., LTD WIFI MODULE -ESP12S". FCC. August 4, 2016. Retrieved 2017-07-17. 
  16. ^ "MOD-WIFI-ESP8266". Olimex. Retrieved 2015-06-25. 
  17. ^ "MOD-WIFI-ESP8266-DEV". Olimex. Retrieved 2015-06-25. 
  18. ^ "Adafruit HUZZAH ESP8266 Breakout". Adafruit Industries. Retrieved 2015-06-25. 
  19. ^ "SparkFun ESP8266 Thing". SparkFun. Retrieved 2015-06-27. 
  20. ^ "KNEWRON smartWIFI". KNEWRON. Retrieved 2016-03-04. 
  21. ^ a b c d e WeMos. "WEMOS". WEMOS. 
  22. ^ "WeMos D1". WeMos. Retrieved 2016-11-30. 
  23. ^ "WeMos D1 R2". WeMos. Retrieved 2016-01-05. 
  24. ^ "WeMos D1 mini". WeMos. Retrieved 2017-06-29. 
  25. ^ "WeMos D1 mini Lite". WeMos. Retrieved 2017-06-29. 
  26. ^ "WeMos D1 mini Pro". WeMos. Retrieved 2017-06-29. 
  27. ^ "Espert". Espert. Retrieved 2016-01-07. 
  28. ^ "Cytron Technologies - ESPresso Lite V2.0". Retrieved 2016-02-10. 
  29. ^ "ESP-ADC DIL18 development board". In-Circuit Wiki. Retrieved 2016-02-03. 
  30. ^ "Watterott ESP-WROOM02-Breakout". Watterott. Retrieved 2016-11-06. 

External links[edit]