Overview

The ESP8266 (and ESP8266EX) is a highly integrated 32-bit Wi-Fi micro-module developed by Espressif Systems. It combines a 32-bit Tensilica Xtensa L106 RISC processor core running up to 160 MHz, full 802.11 b/g/n Wi-Fi radio capabilities, TCP/IP stack, and GPIO peripherals on a single chip.

It is widely available as standalone breakout modules (ESP-01, ESP-12E / ESP-12F) and complete development boards (NodeMCU, Wemos D1 Mini) with USB-to-UART programmers and 3.3V power regulation onboard.

Quick reference

Operating voltage (VCC)3.0 V to 3.6 V DC (3.3 V nominal)
CPU32-bit Tensilica Xtensa L106 RISC (80 MHz / 160 MHz)
SRAM80 KB Instruction RAM + 50 KB Data RAM
External SPI FlashTypically 1 MB (ESP-01) or 4 MB (ESP-12E/F, NodeMCU)
Wi-Fi protocol802.11 b/g/n (2.4 GHz, WPA/WPA2 Personal & Enterprise)
Peak Transmit CurrentUp to 170 mA (during Wi-Fi TX bursts)
Deep Sleep Current~20 µA
Analog ADC Input1 Channel (0.0 V to 1.0 V bare chip / 0.0 V to 3.3 V on NodeMCU)

Pinout

ESP-01 Header Pinout (8-Pin 2x4 0.1" Header)

PinNameTypeDescription
1GNDPowerGround (0 V)
2GPIO2Digital I/OGeneral purpose I/O / Boot config pin (must be HIGH on boot)
3GPIO0Digital I/OGeneral purpose I/O / Boot mode (LOW = Flash mode, HIGH = Normal)
4RXDDigital InputUART Receive line (GPIO3)
5TXDDigital OutputUART Transmit line (GPIO1)
6CH_PD / ENDigital InputChip Enable (MUST be tied HIGH to 3.3V to run)
7RSTDigital InputActive-LOW Hardware Reset
8VCCPowerSupply voltage (+3.3 V DC only)

ESP-12E / ESP-12F Module Strapping Pins & Boot Modes

Boot ModeGPIO15GPIO0GPIO2
Flash Boot (Normal Run)LOW (GND)HIGH (3.3V)HIGH (3.3V)
UART Download (Flash Programming)LOW (GND)LOW (GND)HIGH (3.3V)
SD-Card BootHIGH (3.3V)LOW (GND)HIGH (3.3V)

Specifications

ParameterSymbolMinTypMaxUnitConditions
Operating VoltageVCCV_{CC}3.03.33.6VDC
TX Current (802.11b, +19.5dBm)ITXI_{TX}—170220mAPeak burst power
RX Current (802.11b/g/n)IRXI_{RX}—5660mAActive reception
Modem-Sleep CurrentImodemI_{modem}—1520mACPU active, Wi-Fi disabled
Deep-Sleep CurrentIsleepI_{sleep}—2030µARTC active (RST tied to GPIO16)
GPIO Max Drive CurrentIGPIOI_{GPIO}—1212mAPer pin sink/source
Operating TemperatureTOPT_{OP}-40—125°C

Wiring & Bare-Module Hookup (ESP-01 / ESP-12)

ESP8266 PinConnection TargetNotes
VCC+3.3 V Power SupplyRequires dedicated 3.3V regulator capable of 300 mA
GNDCommon Ground (0 V)Ground connection
CH_PD / EN+3.3 V10 kΩ10\text{ k}\Omega pull-up resistor to 3.3V
RST+3.3 V10 kΩ10\text{ k}\Omega pull-up resistor to 3.3V (Momentary switch to GND to reset)
GPIO15 (ESP-12)Ground10 kΩ10\text{ k}\Omega pull-down resistor to GND
GPIO0+3.3 V (Run) / GND (Program)10 kΩ10\text{ k}\Omega pull-up resistor to 3.3V (Switch to GND to Flash)
GPIO2+3.3 V10 kΩ10\text{ k}\Omega pull-up resistor to 3.3V
Warning

3.3V Logic & Power Supply Requirements:

  • ESP8266 GPIO pins are NOT 5V tolerant. Connecting 5V signals to any GPIO pin risks permanent damage.
  • The 3.3V rail of an Arduino Uno cannot power an ESP8266. Peak Wi-Fi TX current pulses (>200 mA> 200\text{ mA}) will cause the Arduino LDO to collapse, resulting in endless bootloops. Use an external 3.3V LDO (such as AMS1117-3.3) with a 100 μF100\text{ }\mu\text{F} decoupling capacitor.

Common mistakes

  • Powering from Arduino 3.3V pin: Causes continuous bootloops (rst cause:4, bootmode:(3,6)) due to supply rail voltage sag during Wi-Fi initialization.
  • Floating CH_PD / EN pin: Leaving Chip Enable unconnected keeps the internal LDO turned off, rendering the board completely dead.
  • Incorrect strapping pin state at boot: If GPIO15 is pulled HIGH or GPIO0 is held LOW on boot, the chip will refuse to execute application code from SPI flash.
  • Deep Sleep wake-up pin missing: To wake from Deep Sleep, GPIO16 MUST be connected to the RST pin so the internal RTC timer can pulse RST LOW to restart the CPU.

Notes

  • Programmable directly from the Arduino IDE, ESP-IDF, MicroPython, or ESPHome.

Assets & downloads