Arduino Shields v2

Contributors: jimblom, El Duderino
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Shield Form Factor

Every Arduino shield must fit the same form factor as the Arduino it mates to.

Shields designed to work on the Arduino Uno R3 form factor have power and ground pins on one eight (previously six) pin header, and analog pins on a six-pin header next to that. DiAgital pins cover the other edge on the opposite side, an eight-pin header separated from a 10-pin by that weird 0.5" spacing. Some shields also require a connection to the Arduino's ICSP header (the 2x3 programming header on the end).

Shield Pinout

Pin Functionality

Some shields use nearly every available pin on the Arduino, while others only use a couple. Some shields communicate with the Arduino via SPI, I2C, or Serial. Other shields use the Arduino's interrupts, analog inputs, and PWM. When stacking shields it's important to make sure they don't use overlapping pins.

Serial Communication

Asynchronous serial communication concepts: packets, signal levels, baud rates, UARTs and more!

Serial Peripheral Interface (SPI)

SPI is commonly used to connect microcontrollers to peripherals such as sensors, shift registers, and SD cards.

Analog to Digital Conversion

The world is analog. Use analog to digital conversion to help digital devices interpret the world.

Pulse Width Modulation

An introduction to the concept of Pulse Width Modulation.


An introduction to I2C, one of the main embedded communications protocols in use today.

Processor Interrupts with Arduino

What is an interrupt? In a nutshell, there is a method by which a processor can execute its normal program while continuously monitoring for some kind of event, or interrupt. There are two types of interrupts: hardware and software interrupts. For the purposes of this tutorial, we will focus on hardware interrupts.

Additionally, you will also want to ensure that shield pins are compatible with your development board. If a shield was designed with the ATmega328p in mind, the pin functionality may be in a different location. For example, the XBee shield was designed for the Arduino Uno R3 (an ATmega328P-based board). If you were to use the Arduino Leonardo (an ATmega32U4-based board) or the Arduino Mega 2560 (an ATmega2560-based board), you would need to reroute the connection and redefine the pin definitions. For more information, check out the XBee Shield Hookup guide.

Pins Rerouted for Arduino Mega 2560 R3 Pins Rerouted for Arduino Leonardo w/ ATmega32U4
XBee Shield Pins Rerouted for ATmega2560-Based Arduino XBee Shield Pins Rerouted for ATmega32U4-Based Arduino

Logic Levels

Also note that there are several Arduino development boards available now that fit the R3 form factor but run at a different logic level than the standard Uno/RedBoard. For example, the Arduino Uno R3 runs at 5V logic where the RedBoard Artemis runs at 3.3V. Quite a few shields can function just fine with a board running at either logic level but you may run into some erratic behavior with level shifting circuits set up to work best with a 5V system. Another potential issue you may run across with a 3.3V logic Arduino is if the shield pulls any of the pins to a 5V reference voltage through something like a pull up resistor.

Logic Levels

June 3, 2013

Learn the difference between 3.3V and 5V devices and logic levels.

Other Shield Form Factors

There is a great variety of Arduino shields out there -- too many to ever include in this tutorial. While most adhere to the standard Arduino Uno R3 form factor, some shield designs can vary depending on the development board's footprint and environment. Some of these designs include the Thing Plus, Pro Mini, Pro Micro, Arduino Nano, Arduino MKR, and Teensy footprints.

In the next section, we'll go over a handful of the more popular and unique shields designed for the R3 form factor that SparkFun carries.