ESP8266 WiFi Module

ESP8266 is Wi-Fi enabled system on chip (SoC) module developed by Espressif system. It is mostly used for development of IoT (Internet of Things) embedded applications.

The ESP8266 is a low-cost Wi-Fi microchip with full TCP/IP stack and microcontroller capability produced by Shanghai-based Chinese manufacturer Espressif Systems. The ESP8266 is capable of either hosting an application or offloading all Wi-Fi networking functions from another application processor. Each ESP8266 module comes pre-programmed with an AT command set firmware, meaning, you can simply hook this up to your Arduino device and get about as much WiFi-ability as a WiFi Shield offers (and that’s just out of the box)! The ESP8266 module is an extremely cost effective board with a huge, and ever growing, community.

ESP8266 WiFi Module


  • 2.4 GHz Wi-Fi (802.11 b/g/n, supporting WPA/WPA2),
  • General-purpose input/output (16 GPIO),
  • Inter-Integrated Circuit (I²C) serial communication protocol,
  • Analog-to-digital conversion (10-bit ADC)
  • Serial Peripheral Interface (SPI) serial communication protocol,
  • I²S (Inter-IC Sound) interfaces with DMA(Direct Memory Access) (sharing pins with GPIO),
  • UART (on dedicated pins, plus a transmit-only UART can be enabled on GPIO2), and
  • Pulse-width modulation (PWM).

It employs a 32-bit RISC CPU based on the Tensilica Xtensa L106 running at 80 MHz (or overclocked to 160 MHz). It has a 64 KB boot ROM, 64 KB instruction RAM and 96 KB data RAM. External flash memory can be accessed through SPI.

To communicate with the ESP8266 module, microcontroller needs to use set of AT commands. Microcontroller communicates with ESP8266-01 module using UART having specified Baud rate.

There are many third-party manufacturers that produce different modules based on this chip. So, the module comes with different pin availability options like,

  • ESP-01 comes with 8 pins (2 GPIO pins) – PCB trace antenna. (shown in above figure)
  • ESP-02 comes with 8 pins, (3 GPIO pins) – U-FL antenna connector.
  • ESP-03 comes with 14 pins, (7 GPIO pins) – Ceramic antenna.
  • ESP-04 comes with 14 pins, (7 GPIO pins) – No antenna.

ESP8266-01 Module Pinout


  • 3V3: - 3.3 V Power Pin.
  • GND: - Ground Pin.
  • RST: - Active Low Reset Pin.
  • EN: - Active High Enable Pin.
  • TX: - Serial Transmit Pin of UART.
  • RX: - Serial Receive Pin of UART.
  • GPIO0 & GPIO2: - General Purpose I/O Pins. These pins decide what mode (boot or normal) the module starts up in. It also decides whether the TX/RX pins are used for Programming the module or for serial I/O purpose.

To program the module using UART, Connect GPIO0 to ground and GPIO2 to VCC or leave it open. To use UART for normal Serial I/O leave both the pins open (neither VCC nor Ground).

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