Arduino Ethernet Shield W5100

The Arduino Ethernet Shield W5100 is a powerful and reliable expansion board that adds wired Ethernet networking capabilities to your Arduino, transforming it into an internet-connected device in seconds. Built around the popular Wiznet W5100 Ethernet chip, this shield provides a complete hardware TCP/IP stack that handles the heavy lifting of network communication — leaving your Arduino's processing power free for your application.

The W5100 chip is a hardware-implemented network controller that supports up to 4 simultaneous socket connections, with full implementations of TCP, UDP, ICMP, IPv4, ARP, IGMP, and PPPoE. This means your Arduino can act as a web server, web client, FTP client, telnet client, or even a small IoT gateway without struggling under the weight of complex protocol stacks. The chip communicates with the Arduino through the SPI bus (digital pins 11, 12, 13 on Uno; 50, 51, 52 on Mega), with pin 10 used as the chip-select line.

The shield also includes a standard micro-SD card slot, allowing your Arduino to store and serve files such as HTML pages, sensor data logs, configuration files, or images directly over the network. The SD card is accessed through the same SPI bus using pin 4 as its chip-select. With proper handling in software, the W5100 and SD card can work together seamlessly to create powerful mini web servers capable of serving full web pages.

The shield features a standard RJ45 Ethernet jack with integrated link/activity LEDs, making it easy to verify network connectivity at a glance. It uses long wire-wrap headers that pass through the shield, preserving the original pin layout and allowing additional shields to be stacked on top — making it perfect for combining with sensor shields, motor driver shields, or LCD shields.

Compatible with the official Arduino Ethernet library, programming the shield is straightforward. The library includes ready-to-use functions for DHCP, DNS, web servers, and clients, allowing you to establish network connections in just a few lines of code. The board is supported by Arduino Uno, Mega 2560, Leonardo, and most other Arduino models with standard headers.

Pin Usage

• Pin 4: SD Card Chip Select
• Pin 10: W5100 Ethernet Chip Select
• Pin 11 (Uno) / 51 (Mega): SPI MOSI
• Pin 12 (Uno) / 50 (Mega): SPI MISO
• Pin 13 (Uno) / 52 (Mega): SPI SCK
• Pin 53 (Mega only): Must be kept as output (hardware SS)

Specifications

• Product Type: Ethernet and Storage Expansion Shield
• Network Controller: Wiznet W5100
• Network Interface: RJ45 Ethernet Port (10/100 Mbps)
• Communication Protocol: TCP/IP (TCP, UDP, ICMP, IPv4, ARP, IGMP, PPPoE)
• Maximum Simultaneous Sockets: 4
• Communication Bus: SPI (via ICSP header)
• Data Storage: Micro-SD Card Slot (FAT16/FAT32 supported)
• Logic Voltage: 5V (Arduino-compatible)
• Control Interface: SPI Bus
• Mounting Type: Arduino Shield (Stackable)
• Dimensions: 68 mm × 53 mm
• Compatible Boards: Arduino Uno, Mega 2560, Leonardo, Duemilanove
• Software Library: Arduino Ethernet Library (Built-in to Arduino IDE)
• LED Indicators: Power, Link, Activity, Speed, Collision
• Compliance: RoHS Compliant

Applications

• Web Servers — hosting Arduino-controlled web pages
• IoT Devices — sending sensor data to cloud platforms (ThingSpeak, MQTT brokers)
• Home Automation — wired network-controlled lights, fans, and appliances
• Network Monitoring Tools — DIY ping monitors and uptime trackers
• Data Loggers — saving environmental data to SD card and uploading via network
• Remote Sensor Networks — wired sensor nodes in industrial environments
• Email Notification Systems — sending alerts based on sensor triggers
• Time-Synchronized Devices — fetching NTP time over the network
• Educational & STEM Projects — teaching networking and TCP/IP concepts
• Smart Building Controls — networked HVAC, lighting, and security systems
• DIY File Servers — small SD-card-based network file sharing
• Industrial Automation — Modbus TCP and other industrial protocols
• Camera Triggers — networked photography and surveillance setups
• Game Servers (Lightweight) — simple multiplayer Arduino-based games
• Telemetry Systems — collecting data from remote stations
• Network-Based Robotics — controlling robots over LAN/WAN
• Replacement Shield — for damaged W5100 boards in existing projects
• Wired Alternative to WiFi — when reliability and stability are critical