Product Overview
The ESP-WROOM-02 (4MB) is a highly integrated, certified Wi-Fi module developed by Espressif Systems, the original creator of the ESP8266 ecosystem. This variant features 4 MB (32 Mbit) of SPI flash memory, doubling the storage capacity of the standard version and providing significantly more space for complex applications, web interfaces, and OTA (Over-The-Air) updates .
At its heart lies the ESP8266EX chip—a 32-bit Tensilica L106 RISC processor running at up to 160 MHz, with 50 kB of RAM available for user applications . The module supports 802.11 b/g/n Wi-Fi protocols at 2.4 GHz, with a built-in PCB antenna that delivers up to +20.5 dBm output power and excellent receiver sensitivity down to -98 dBm .
Unlike many third-party ESP8266 modules, the ESP-WROOM-02 is designed and manufactured by Espressif, ensuring full compliance with RF certifications including FCC, CE-RED, and TELEC, making it the ideal choice for commercial products requiring regulatory approval . It comes preloaded with AT command firmware, allowing you to add Wi-Fi connectivity to any microcontroller using simple serial commands, or you can reprogram it as a standalone IoT processor using the Arduino IDE, MicroPython, or ESP-IDF.
Key Features
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Official Espressif Module: Designed and manufactured by Espressif Systems, the creators of the ESP8266, ensuring the highest quality and reliable RF performance .
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4 MB Flash Memory: Equipped with 4 MB (32 Mbit) of SPI flash memory—double the capacity of standard ESP-WROOM-02 modules—providing ample storage for complex firmware, web interfaces, and OTA (Over-The-Air) updates .
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Integrated 32-bit Processor: Powered by the Tensilica L106 32-bit RISC processor running at up to 160 MHz, capable of running application code independently without an external microcontroller .
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Complete Wi-Fi Solution: Supports 802.11 b/g/n protocols at 2.4 GHz with integrated PCB antenna. Delivers up to +20.5 dBm output power with receiver sensitivity down to -98 dBm .
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Preloaded AT Command Firmware: Ships with industrial-grade AT firmware that allows control via simple serial commands, enabling rapid integration with any microcontroller .
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Multiple Operating Modes: Supports Station (STA), SoftAP (Access Point), and SoftAP + STA modes, enabling devices to connect to existing networks or create their own.
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Rich Peripheral Interfaces: Provides UART, HSPI, I2C, I2S, PWM, and 10-bit ADC interfaces, allowing connection to a wide variety of sensors, actuators, and display devices .
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Ultra-Low Power Consumption: Features multiple sleep modes with deep sleep current as low as 20 µA and standby power consumption less than 1.0 mW (DTIM3), making it ideal for battery-powered applications .
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Global Regulatory Certifications: Certified with FCC, CE-RED, TELEC, and KC, simplifying the certification process for commercial products .
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Wide Operating Temperature: Rated for operation from -40°C to +85°C, suitable for demanding industrial environments and outdoor installations .
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Compact SMD Package: Measures just 18.0 mm × 20.0 mm × 2.8 mm with 18 castellated pins, designed for automated surface-mount assembly .
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Upgradable Firmware: Supports local serial flashing, OTA (Over-The-Air) updates, and host download for flexible firmware management.
Technical Specifications
Pinout & Interface Guide
The ESP-WROOM-02 features 18 castellated pins for easy soldering to a PCB or connection via a development board .
Boot Mode Configuration
The module’s boot mode is determined by the state of GPIO0, GPIO2, and GPIO15 :
Critical Notes:
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GPIO15 must be pulled LOW during boot for both modes
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GPIO2 must be pulled HIGH during boot
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GPIO0 must be LOW to enter programming mode, HIGH for normal operation
Usage Guide
Power Supply Requirements
The ESP-WROOM-02 requires a stable 3.3 V DC power supply capable of providing at least 500 mA during peak operation . For reliable operation:
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Use a low-dropout regulator (LDO) such as AMS1117-3.3 or LM1117-3.3
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Add a 10 µF to 100 µF electrolytic capacitor and a 0.1 µF ceramic capacitor close to the VCC pin for power decoupling
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Do not apply 5 V to any pin—this will permanently damage the module
Programming the ESP-WROOM-02
Method 1: Using a USB-to-TTL Adapter
This is the simplest method for programming the module:
Enter Programming Mode:
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Connect GPIO0 (pin 10) to GND
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Connect GPIO15 (pin 13) to GND
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Connect GPIO2 (pin 12) to VCC (pull HIGH)
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Connect EN (pin 17) to VCC (pull HIGH)
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Apply power or pulse RST LOW
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Upload firmware via Arduino IDE or esptool
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After upload, disconnect GPIO0 from GND and reset
Setting Up Arduino IDE for ESP-WROOM-02
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Install ESP8266 Board Package:
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Open Arduino IDE → File → Preferences
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Add to “Additional Boards Manager URLs”: https://arduino.esp8266.com/stable/package_esp8266com_index.json
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Tools → Board → Boards Manager → Search “esp8266” → Install
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Select Board:
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Configure Flash Settings:
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Flash Size: 4 MB (16 Mbit)
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Upload Speed: 115200 (or 921600 for faster uploads)
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CPU Frequency: 80 MHz (or 160 MHz for higher performance)
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Flash Mode: DOUT (compatible)
AT Command Example
With the default AT firmware, the ESP-WROOM-02 can be controlled via simple serial commands at 115200 baud :
AT // Check communication
AT+GMR // Check firmware version
AT+CWMODE=1 // Set to Station mode
AT+CWJAP="SSID","PASSWORD" // Connect to Wi-Fi
AT+CIFSR // Get IP address
AT+CIPSTART="TCP","192.168.1.100",8080 // Open TCP connection
AT+CIPSEND=5 // Send data
> HELLO // Data to send
Updating AT Firmware
If your module has an older firmware version, you can update it over Wi-Fi using the AT+CIUPDATE command :
// Check current version
AT+GMR
// Connect to Wi-Fi
AT+CWMODE=1
AT+CWJAP="SSID","PASSWORD"
// Start firmware update
AT+CIUPDATE
// Wait several minutes for completion
// Module will automatically restart
// Verify update
AT+GMR
Basic Arduino Example Code
#include <ESP8266WiFi.h>
const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
void setup() {
Serial.begin(115200);
Serial.println("\nESP-WROOM-02 Wi-Fi Test");
WiFi.begin(ssid, password);
Serial.print("Connecting to Wi-Fi");
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("\nConnected successfully!");
Serial.print("IP Address: ");
Serial.println(WiFi.localIP());
}
void loop() {
}
Using WiFiEspAT Library
For easy integration with Arduino, the WiFiEspAT library allows you to control the module using Arduino-style Wi-Fi commands :
#include <WiFiEspAT.h>
#define RX_PIN 16
#define TX_PIN 17
#define AT_BAUD_RATE 115200
const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
void setup() {
Serial.begin(115200);
Serial1.setRX(RX_PIN);
Serial1.setTX(TX_PIN);
Serial1.begin(AT_BAUD_RATE);
WiFi.init(Serial1);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(1000);
}
Serial.println("Connected to Wi-Fi");
Serial.print("IP: ");
Serial.println(WiFi.localIP());
}
Development Environments
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Arduino IDE: User-friendly environment with extensive libraries
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PlatformIO: Professional development environment with ESP8266 support
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ESP-IDF: Official Espressif development framework for advanced users
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MicroPython: Python-based development for rapid prototyping
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NodeMCU (Lua): Lua-based firmware for quick project development
Q: What is the difference between ESP-WROOM-02 and third-party ESP8266 modules like ESP-01 or ESP-12?
The ESP-WROOM-02 is the official Espressif module, designed and manufactured by the creators of the ESP8266 chip. Key differences include:
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Quality assurance: Rigorous testing and certification by Espressif
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Global certifications: FCC, CE, Wi-Fi Alliance, RoHS, REACH certified
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Consistent performance: Optimized RF design for reliable wireless performance
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Support: Official documentation and support from Espressif
Q: Can the ESP-WROOM-02 operate as a standalone microcontroller?
Yes. The ESP8266EX chip includes a 32-bit processor capable of running application code directly. You can program it with Arduino, MicroPython, or the ESP8266 SDK without requiring an external microcontroller
Q: How much flash memory does the ESP-WROOM-02 have?
The module is equipped with 2 MB (16 Mbit) of SPI flash memory . This is sufficient for most IoT applications, web interfaces, and OTA (Over-The-Air) updates.
Q: What is the maximum range of the Wi-Fi connection?
With its PCB antenna (2 dBi gain), the ESP-WROOM-02 achieves ranges of up to 100-200 meters in open space. In practical indoor applications with walls and obstacles, the range is typically 30-50 meters.
Q: Does the ESP-WROOM-02 support Bluetooth?
No. The ESP8266 series is Wi-Fi only. For Bluetooth capability, consider the ESP32 series modules like ESP32-WROOM-32.
Q: Is this module still recommended for new designs?
Important: Espressif has designated the ESP-WROOM-02 as “Not Recommended for New Designs” (NRND) as of 2025 . For new projects, consider the successor models like ESP8684-WROOM-02C (ESP32-C3 based) which offer improved performance and Bluetooth capability.
Q: What voltage does the ESP-WROOM-02 require?
The module requires a stable 3.3 V DC power supply with an operating range of 2.7 V to 3.6 V . Never apply 5 V to the VCC pin or any GPIO pin—this will permanently damage the module.
Q: How much current does the ESP-WROOM-02 draw?
Current consumption varies by operating mode :
Q: Can I power the ESP-WROOM-02 with batteries?
Yes. The module’s low deep sleep current (20 µA) makes it suitable for battery-powered applications. A single 18650 lithium-ion cell (3.7 V) can be used with a 3.3 V LDO regulator. With proper deep sleep management, battery life of months is achievable.
Q: Why does my ESP-WROOM-02 not boot?
Common boot issues include :
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GPIO15 not pulled LOW during boot
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GPIO0 pulled LOW (this enters programming mode)
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GPIO2 not pulled HIGH during boot
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EN/CH_PD not connected to VCC
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Insufficient power supply (current sag during startup)
Q: How do I put the ESP-WROOM-02 into programming mode?
To enter programming (UART download) mode :
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Pull GPIO0 LOW (connect to GND)
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Pull GPIO15 LOW (connect to GND)
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Pull GPIO2 HIGH (connect to VCC)
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Pull EN HIGH (connect to VCC)
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Apply power or pulse RST LOW
Q: Why can't I upload code to my ESP-WROOM-02?
Common upload issues:
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GPIO0 not held LOW during power-on/reset
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Incorrect serial connections (TX to RX, RX to TX)
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Insufficient power supply (USB-to-TTL adapters may not provide enough current)
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Wrong board selection in Arduino IDE (select “Generic ESP8266 Module”)
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Missing pull-down on GPIO15
Q: What is the default baud rate for AT commands?
The default baud rate is 115200 bps . The bootloader outputs diagnostic information at 74880 baud during startup.
Q: How do I update the AT firmware?
You can update the AT firmware over Wi-Fi using the AT+CIUPDATE command :
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Connect to a Wi-Fi network with AT+CWJAP
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Send AT+CIUPDATE
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Wait several minutes for the update to complete
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The module will restart automatically
Q: Can I use the ESP-WROOM-02 with Arduino IDE?
Yes. Install the ESP8266 board package via Boards Manager, then select “Generic ESP8266 Module” as the board. Configure the flash size (2 MB) and upload speed appropriately .
Q: What can I build with the ESP-WROOM-02?
Popular applications include :
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Smart home devices: Lighting control, smart plugs, thermostats, window/door sensors
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Environmental monitoring: Temperature, humidity, air quality stations
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Industrial wireless sensors: Equipment monitoring, predictive maintenance
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Weather stations: Remote data logging and monitoring
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Wireless data acquisition: Replacing cables with wireless links
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Consumer electronics: Adding Wi-Fi connectivity to existing products
Q: Is the ESP-WROOM-02 suitable for commercial products?
Yes. The ESP-WROOM-02 is certified with FCC, CE, Wi-Fi Alliance, RoHS, and REACH . This makes it ideal for commercial products requiring regulatory approval, significantly reducing certification costs and time.
Q: What firmware options are available?
Popular firmware choices include :
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AT Command Firmware: Default firmware for co-processor mode
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NodeMCU (Lua): Open-source Lua-based firmware for easy programming
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MicroPython: Python-based development for rapid prototyping
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Arduino/C++: Custom code via Arduino IDE
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ESP-IDF: Official Espressif development framework
Q: Does the ESP-WROOM-02 support OTA (Over-The-Air) updates?
Yes. The 2 MB flash memory supports OTA firmware updates, allowing you to upload new code wirelessly without physically connecting to the module .
