Ultimate Arduino Uno Hardware Manual Preview

27 March 2021

Preview the Ultimate Arduino Uno Hardware Manual below where the full introduction chapter can be found, and the first couple of pages are displayed for each of the other chapters. A preview is also available on the Elektor page for the Ultimate Arduino Uno Hardware Manual on the Elektor website.

The preview that follows may appear slightly different from the printed book because it has been published to automatically resize for different devices connecting via the web. This means that the layout, font size and image size may be different from the printed book, but the content is still the same. It is intended for interested buyers to get a better idea of the contents of the book. Also see the Table of Contents page for a full listing of the book contents by sections and headings. There is also more spacing between paragraphs for easier reading on a screen.

The following is copyrighted material from the Ultimate Arduino Uno Hardware Manual for previewing purposes.


Welcome to the Arduino Uno Hardware Manual, a reference and user guide for the Arduino Uno hardware and firmware. This manual provides up to date hardware information for the popular Arduino Uno, the easy to use open-source electronics platform used by hobbyists, makers, experimenters, educators and professionals.

Why Buy this Arduino Uno Hardware Manual?

There are four main reasons to buy this book besides just wanting a handy reference manual for the Arduino Uno hardware and firmware for use on the workbench. These reasons are discussed below.

1) All the Hardware Information in One Place
Although there is a lot of information about the Arduino Uno hardware available online, it is spread out over many pages and websites. Having all of the Arduino Uno hardware information in one place, in this concise guide, is convenient and a time saver. This is especially true for new Arduino users who may not even know what to look for when getting familiar with the Arduino Uno hardware, for example, how to extend the hardware, how to add external data memory, how to connect hardware to Arduino pins in current sinking and current sourcing configuration. It also includes practical information such as how to replace the main microcontroller, which firmware needs to be loaded to a new microcontroller and which other settings must be changed for it to work. In addition, this manual has detailed hardware technical information, a pin reference chapter, basic interfacing information, a power reference chapter, information on all firmware programs loaded on an Arduino Uno, the circuit diagram and component list, fault finding and testing steps, as well as hardware mechanical dimensions and measurements.

2) Integrity of Information
Information on the internet about Arduino or any other subject may or may not be technically correct. Discerning which information is correct and which is incorrect is a problem, especially for those users who are new to electronics. Even hardware specifications from Arduino themselves are often badly specified or even incorrectly specified. This manual provides hardware information on the Arduino Uno that has been carefully checked and verified to be correct.

3) Presentation of Information
Each topic or subject in this book has been broken down into smaller parts and carefully explained and described. For this reason, each chapter contains many sections, each with its own sub-heading and section number for easy reference and cross-reference. Numerous illustrations and figures are included for easier understanding of explanations and for quick and easy reference.

4) Information Not Available Elsewhere
This book contains some information that is not available online, or is hard to find. It also offers unique views and illustrations of the hardware that reveal some interesting aspects of the Arduino Uno hardware that is not obvious when looking at the circuit diagram or other sources of information.

Target Audience

This manual has been written for anyone interested in the Arduino Uno who would like an easy to use hardware reference, including hobbyists, makers, experimenters, teachers, students, and professionals such as electronic engineers.


It is assumed that the reader of this manual has at least used the Arduino Uno on a basic level and has some basic knowledge of electronics. This is not a book that explains the basics of electronics, but assumes that the reader already has the knowledge to understand terms such as voltage and current, and knows what electronic components such as resistors and transistors are. In any case, this is the basic knowledge that is required to use an Arduino. Those readers who do not have this basic knowledge must at least be willing to learn, by using additional resources, be it via the internet or by using other books on the subject.

Hardware Requirements

At a minimum, an Arduino Uno will obviously be required, as well as a computer with which to program the Arduino board. This book mainly references the Arduino Uno revision 3 (REV3 or R3) board which is the latest Arduino Uno at the time of writing. It also mentions earlier versions of the Arduino Uno when necessary and makes some reference to clone or compatible boards. For advanced use and programming firmware to the Arduino Uno, one of several USB programmers can be used – see the text for more details, but most users will not need to do this, unless updating firmware on a new microcontroller, and even then there are cheaper alternatives such as using one Arduino to update the firmware on a second Arduino.

In the pin reference and interfacing chapter, an electronic breadboard and jumper wires are used to show how to interface LEDs, transistors, a relay, an external TWI memory chip and an SD card adapter. These are just interfacing examples and users will only need the components for a particular project or interfacing example that they are interested in. Hardware testing requires at least a multimeter. Some tests require an oscilloscope, but it is not essential for every user and is only used in a small section of the book.

Software Requirements

Without software, an Arduino Uno does absolutely nothing. For this reason, although this is a hardware manual, the free Arduino IDE programming environment must be installed. This enables Arduino programs or sketches to be loaded to the Arduino Uno to operate and test the hardware.

All software used in this book is either free and open-source, such as the Arduino IDE software, or free software that is not open-source. All software used can easily be downloaded from the internet at no cost. Other software, besides the Arduino IDE, is optional and will only need to be installed if required for certain tasks.

What is Covered and What’s Not Covered

This book is primarily about hardware on an Arduino Uno board, including technical information, a pin reference, power supply information, firmware details, circuits and parts list, fault finding and measurement, as well as mechanical information, but has to include some software, in the form of user programs or sketches, in order to get the hardware to work. That being said, it does not cover software programming in great detail, but does provide references to the appropriate example sketches in the Arduino IDE and online documentation where necessary. Most of the functionality of an Arduino Uno comes from the main microcontroller on the board. This microcontroller is covered by the text in the context of Arduino and how it is set up and used by the Arduino IDE and its libraries. Advanced use of some of the internal hardware in the main microcontroller that is not available in the Arduino IDE and libraries is not covered, except to provide a pin reference for these advanced features that shows which Arduino pins are mapped to advanced hardware. Users who want to use the advanced hardware that is not available in the Arduino IDE or libraries must reference the datasheet for the main microcontroller.

How to Use this Book

It is suggested that this book is first read through once to get a good idea of its contents and a better understanding of the Arduino Uno hardware, it can then be used as a reference manual. Although this book has been written as a manual, it is not dry like some manuals or textbooks. Anyone interested in Arduino should find it an enjoyable read.

For electronic engineers or competent hobbyists who have used other microcontroller boards, but not an Arduino Uno, this book provides an easy introduction to the Arduino Uno hardware that will get new users started quickly with the board. The first two chapters of the book are basically a hardware user manual, while the remaining chapters are more like a reference manual, although there is some overlap between the two.

When using the book for reference, use the index to find specific topics and use appendix A to quickly find technical specifications. Appendix A has a cross reference for each technical specification that references the same specification in the main text, which provides detailed information. Each section in the book cross references related material in other sections and chapters. The table of contents is also useful for referencing information, as it is a list of every section in the book.

Accompanying Resources

Accompanying resources can be found on the Elektor (www.elektor.com) web page for this book, and on the author’s supporting website (wspublishing.net) which includes links to all of the online resources so that they do not need to be typed in manually. Arduino software sketches used in the book are also available from the supporting website.

Disclaimer, Errors and Corrections

Although this manual is not an official Arduino manual, or endorsed by Arduino in any way, it has been written and thoroughly checked by a competent electronic engineer. The information in this manual has been carefully checked and proof read, but this is not a claim of infallibility, and this manual, like any work, is subject to typos and small errors that may have been missed during the proof reading process. In the event that you do find an error or typo, please use the accompanying website wspublishing.net to report it. This will be a big help to others as any corrections will be published on the supporting website.

A Note from the Author

Thank you for purchasing this manual! I hope that you thoroughly enjoy reading this book and using it as a reference. Please give an honest review of this book on the web page for this book at the Elektor website (www.elektor.com). This will provide feedback to the author that can be used to improve future versions of this manual. When writing a review, bear in mind that this book is an Arduino Uno hardware manual and not a software or electronics book. Review the book contents in light of its title and stated purpose. Also bear in mind that some information in this book is repeated because of the layout of the book – with chapter 1 being an overview of the Arduino Uno, chapter 2 containing technical information and chapter 3 a pin reference, some information is repeated, but more details are added in each chapter. The alternative to this is to lump everything related together, in which case the book can not be laid out in an easier to read format that builds the information up from a top level view of the hardware followed by more details on each aspect of the hardware.

Chapter 1 • Arduino Uno Overview

Before taking a closer look at each aspect of the Arduino Uno hardware in greater depth, it is necessary to get a top level overview and general understanding of the Arduino Uno. This chapter, together with chapter 2, can be thought of as a "hardware user manual" for the Arduino Uno and covers all of the basics that are needed before a more comprehensive study of the Arduino Uno hardware that is contained in the chapters that follow.

Included in this chapter is a general overview of the Arduino Uno, its main parts, and how to extend its hardware.

Basics of the firmware, the software that comes factory loaded on a new Arduino Uno board, is explained. The chapter wraps up with board handling precautions, a brief history of the Arduino Uno and the hardware revisions that it has been through, some information on first time use, and basic testing.

In this Chapter

  • A top level view of the Arduino Uno hardware and functionality
  • A brief look at the Arduino Uno firmware and what it does
  • Board handling and usage precautions
  • Arduino Uno history and revisions
  • First time use and basic testing
  • References to quickly find information on the Arduino Uno

1.1 Arduino Uno Description and Functionality

The Arduino Uno is a single board computer that uses a microcontroller as its main processor to run software loaded via the Arduino IDE or other programming environment. It comes in two different versions, namely, the Arduino Uno and Arduino Uno SMD. These boards are identical except for the physical package of the main microcontroller.

1.1.1 Arduino Uno

Most users will want to get the Arduino Uno (Figure 1.1) rather than the Arduino Uno SMD board because it has a socket that houses the main microcontroller. This allows easy replacement of the microcontroller should it be damaged or bricked up by software. The main microcontroller is the 28-pin chip that can be seen above the text "POWER" and "ANALOG IN" in Figure 1.1.

Top View of an Arduino Uno Revision 3
Figure 1.1: Top View of an Arduino Uno

1.1.2 Arduino Uno SMD

On the Arduino Uno SMD board, the main microcontroller is a surface mount device (SMD) which can be seen above the word "POWER" in Figure 1.2. This means that it can not easily be replaced if it is ever damaged, as it is directly soldered to the top of the board. It is almost impossible to replace this microcontroller without using a professional soldering rework station.



Chapter 2 • Hardware Technical Information

A description of the Arduino Uno hardware technical information is contained in this chapter, split up into various categories. This chapter and chapter 1 are the hardware user manual chapters of this book.

Whereas chapter 1 gave a broad overview of the Arduino Uno hardware, this chapter gives more specific technical information on the hardware. It "zooms in" to the details of the Arduino Uno and gives more information on the main microcontroller, memory types and sizes, power supply technical details, technical specifications on the programming and user headers, and other hardware on the board.

In this Chapter

  • Arduino Uno microcontroller and memory
  • External and USB power specifications and connection
  • Board operating frequency
  • LED indicator and reset button information
  • Header sockets pinout and detailed pin functions
  • Programming headers pinout and functions

2.1 Microcontroller

The main microcontroller on an Arduino Uno is an ATmega328P-PU 8-bit AVR from Microchip. On the Arduino Uno SMD, the main microcontroller has a part number of ATmega328P-MU. Essentially they are the same device from the same microcontroller family, but the last two digits of the part number differ as they are manufactured in different physical housings or packages. Table 2.1 shows the Arduino Uno boards with order codes, microcontroller part number and microcontroller chip packages.

Table 2.1: Arduino Uno Boards and Microcontroller Part Numbers
BoardBoard CodeMicrocontrollerChip Package
Arduino UnoA000066ATmega328P-PUPDIP
Arduino Uno SMDA000073ATmega328P-MUQFN

On the Arduino Uno, the ATmega328P-PU is housed in a 28-pin Plastic Dual Inline Package (PDIP) which can be plugged into and removed from the socket on the board. Figure 2.1 shows two ATmega328P-PU microcontroller chips that can be used to replace the same device on an Arduino Uno board, while the Arduino Uno SMD has its surface mounting ATmega328P-MU housed in a Quad Flat No-Lead (QFN) package.

Two ATmega328P-PU Microcontroller Chips in 28 Pin PDIP Housings
Figure 2.1: Two ATmega328P-PU Microcontroller Chips in 28 Pin PDIP Housings

Some clone or Arduino Uno compatible boards use yet a different microcontroller package, although still the same ATmega328P device. The microcontroller on the Arduino Uno compatible board in Figure 1.9 of chapter 1 is housed in a Thin plastic Quad Flat Package (TQFP). It is bigger than the QFN package, but still surface mount soldered to the top of the board, so is not easily replaceable like a socketed chip.



Chapter 3 • Pin Reference and Interfacing

The reference part of this book starts with this chapter which is an Arduino Uno pin reference with interfacing examples.

Use this chapter as a quick reference to find pin names, alternate pin functions and the mapping of the ATmega328P pins to the Arduino socketed headers and pin header.

Although this book is a hardware manual for the Arduino Uno and not a book that teaches basic electronics, it does include basic interfacing examples to help users with connecting various electronic components to an Arduino. The interfacing examples are used to illustrate various interfacing techniques and principles.

In this Chapter

  • Arduino Uno pin names, functions and alternate functions
  • Arduino Uno to main microcontroller (ATmega328P) mapping
  • Why an LED must be interfaced using a series resistor
  • Current sourcing and sinking configurations
  • Pull-up and pull-down resistors on inputs
  • TWI and SPI serial buses
  • Serial port / UART
  • Various interfacing examples

3.1 Pin Default and Alternate Functions

Figure 3.1 on the next page shows the default Arduino Uno pin functions as well as the alternate functions such as pins used for TWI and SPI serial buses. This figure is very revealing in that it shows what is really happening with the pins, especially the TWI and SPI pins, where the same pins appear on more than one connector.

3.1.1 Shared TWI Pins

Notice in Figure 3.1 that the TWI pins, SCL and SDA, are shared with analog input pins A5 and A4, but are labeled A5 and A4 on the analog input group of pins. These same pins are routed to the other side of the board where they are labeled SCL and SDA (on Arduino Uno R3 boards, not present on earlier revision boards). In other words there are no additional SCL and SDA TWI pins on Arduino Uno R3 boards, these pins are electrically connected to A5 and A4 on the other side of the board.

Because the TWI pins are shared on an Arduino Uno, this means that if these pins are needed for their TWI function, then only four analog input pins (A0 to A3) are available to use as analog inputs. Bear this in mind if ever designing a shield or building a prototype shield. For compatibility with other shields, avoid the use of A4 and A5 as analog inputs if possible, because other shields may use them as TWI pins. If they do, then they won’t be able to be stacked with shields that use A4 and A5 as analog input pins.

3.1.2 Shared SPI Pins

SPI bus pins appear on digital input / output pins 10 to 13. If these pins are used for SPI, then they can no longer be used as input / output pins, and PWM on pins 10 and 11 will no longer be available.

Notice in Figure 3.1 that three of these pins appear on the ICSP header, namely pins 11, 12 and 13. When an external programmer is connected to the ICSP header, it will also be electrically connected to whatever circuit is connected to pins 11, 12 and 13.

As with the TWI pins, when designing a shield or building a prototype shield, avoid using pins 10 to 13 so that the shield will be compatible with shields that use these pins for their SPI functionality. Start designing a shield by using pins that are not multiplexed with other pin functions first. If there are not enough pins, then the SPI or TWI pins can be used, but compatibility with other shields may be lost.



Chapter 4 • Power Reference

In this power reference chapter for the Arduino Uno, the power supplies from both USB and external sources are explained. Specifications for external and USB power are included.

Power supply circuits on the Arduino Uno board are simplified by breaking them up into sections in the circuit diagram. Each section is then explained.

In this Chapter

  • Power sources and specifications
  • On-board power supply and regulator circuit diagram
  • Power supply protection

4.1 Power Supply Specification

This section summarizes the power supply specification of an Arduino Uno in the categories that follow.

4.1.1 Operating Voltage

The Arduino Uno operates at 5V which is derived either from the USB 5V or from an external power supply that is dropped to 5V by the on-board regulator. The on-board 5V regulator is a 1.0A regulator with its output voltage trimmed to ±1.0%.

In addition to the 5V regulator on the Arduino Uno, a 3.3V regulator drops the 5V supply to 3.3V which is available on the Arduino 3.3V pin. This regulator has an output voltage tolerance of 1.5%. The 3.3V regulator can deliver a maximum current of 150mA.

Cross refer to section 3.3.7 for information on the Arduino Uno power pins.

4.1.2 USB Power Input

USB power from a USB 2.0 port is specified as 5V ± 5% and up to 500mA current. The USB 5V is protected by a resettable fuse that will disconnect the USB 5V should more than 500mA be drawn from the USB port. This fuse has a small resistance which means that as more current is drawn from the USB port, the voltage drop across the fuse will increase. The actual voltage supplied to the Arduino will therefore be the USB voltage minus this small volt drop. Cross refer to section 2.4.1 and 2.4.2 for information on USB power and USB cable specification.

4.1.3 External Power Jack Input

An external power input of 7 to 12V DC can be supplied to the power jack input that is found on the same side of the board as the USB connector. Arduino specify the limits of this input as 6 to 20V and warn that a voltage less then 7V may result in the 5V regulator supplying less than 5V which may make the board unstable. A voltage more than 12V can cause the 5V regulator to overheat and damage the board. See the next section for the pinout and polarity of the external power jack.



Chapter 5 • Arduino Uno Firmware and Bootloader

Firmware is present on both the main Arduino Uno microcontroller and the USB to serial bridge microcontroller. This firmware is factory loaded when the Arduino Uno is manufactured.

Firmware on the main microcontroller is known as the bootloader and allows software sketches to be loaded to the Arduino from the Arduino IDE via the USB connection.

The USB to serial bridge microcontroller on the Arduino Uno has DFU bootloader firmware and firmware that gives it the USB to serial bridge functionality. The DFU bootloader allows the USB to serial firmware to be updated using the USB connection without the need for an external programmer.

This chapter explains all of the firmware found on the Arduino Uno.

In this Chapter

  • Updating the USB to serial firmware using DFU
  • Using Atmel Studio to back up and load new firmware
  • How to reload the USB to serial bridge microcontroller firmware using ICSP
  • Loading the main microcontroller bootloader to a new ATmega328P chip
  • Microcontroller fuse settings
  • Purpose of the RESET-EN solder jumper

5.1 Updating the USB to Serial Bridge Firmware using DFU

The most basic task that an Arduino user can do with the ATmega16U2 microcontroller is to update its operational firmware using the DFU (Device Firmware Update) method. This means that the firmware or software that gives this device its USB to serial bridge function can be updated using the USB port on the Arduino Uno. Most Arduino users should never need to do this, however it is included in this manual to make it complete. Advanced users may also want to use the DFU programming method to put their own custom software into the ATmega16U2. DFU programming requires no external programmer or additional hardware device. Some additional software will need to be downloaded to do the programming.

For Windows computers, download the FLIP (Flexible In-system Programmer) software from Microchip at www.microchip.com/developmenttools/ProductDetails/FLIP For additional information on Arduino DFU programming and for DFU programming using Linux and Mac, see www.arduino.cc/en/Hacking/DFUProgramming8U2 on the Arduino website. A brief description of DFU programming an Arduino Uno using the Microchip FLIP software on a Windows computer follows.

Before updating the ATmega16U2 firmware, download and install the FLIP software, as mentioned in the previous paragraph. Connect the Arduino Uno to a USB port of the computer, as would be done to upload a sketch. Connect the RESET pin of the ATmega16U2 ICSP header to GND and then disconnect it in order to reset the ATmega16U2. Make sure to connect to the RESET signal on the ICSP header near the USB connector and not the one at the end of the board. Refer to Figure 3.21 in section 3.5 of chapter 3 for the pinout of the ICSP header. The RESET pin of the header can be connected to GND on the header or on one of the header sockets at the edge of the board.



Chapter 6 • Circuit Diagram and Components

Although the circuit diagram for the Arduino Uno is available online in both PDF and Eagle EDA formats, this chapter breaks the circuit diagram up into easier to reference and understand sections.

This chapter also includes the component list of all of the parts found on the Arduino Uno board and in the schematic, as well as the location of parts on the board itself.

Parts are usually difficult to locate on the board, especially the smaller parts such as resistor packs and capacitors, because the board is compact and there is no space to silkscreen reference designators for the parts. The diagram in this chapter that shows the location of all components on the board is a great reference that can be used to easily locate any component.

In this Chapter

  • Arduino Uno block diagram
  • Arduino Uno circuit diagram split into three easy to reference figures
  • Component list for the Arduino Uno
  • Location of parts on the board

6.1 Circuit Diagram

The circuit diagram for REV 3 Arduino Uno boards follows in this chapter and is shown as a block diagram that consists of three main parts, namely, the power supply circuit, the USB microcontroller circuit and the main microcontroller circuit with header sockets. Each of these three parts are then presented as separate circuits in the sections that follow.

6.1.1 Block Diagram

The block diagram, seen in Figure 6.1, is a top level view of the Arduino Uno circuit diagram that shows how the different parts of the circuit interconnect. The power supply circuit is supplied with power from the 2.1mm jack and from the USB 5V. This circuit then supplies 5V to the rest of the Arduino and 3.3V to the 3.3V pin. The USB microcontroller circuit connects to the main microcontroller circuit via the TX and RX serial port lines and reset line via C5. This allows the Arduino IDE to reset the main microcontroller in order to start its bootloader which then allows a new sketch to be loaded to the main microcontroller using the TX and RX lines. GND is not shown in the block diagram, but is common throughout. Vin is also omitted in the figure, but connects from the 2.1mm jack through a diode to a pin on the header sockets.

Arduino Uno Block Diagram
Figure 6.1: Block Diagram of Arduino Uno Schematic or Circuit Diagram



Chapter 7 • Fault Finding and Measurement

This chapter is dedicated to fault finding on the Arduino Uno. Basic fault finding techniques are covered. An explanation of how to remove a faulty microcontroller from an Arduino Uno and replace it with a new one is included.

In order to test an Arduino Uno board, various measurements need to be made. Test points on the board are shown in order to make voltage measurements to compare to when testing a faulty board. Both DC voltage measurements that can be tested with a multimeter and various AC waveform measurements are covered that can be measured using an oscilloscope.

Examples that capture PWM, UART, TWI and SPI signals on an oscilloscope in this chapter can be used as a reference when setting up an oscilloscope to test these signals on a project.

In this Chapter

  • Basic fault finding on the Arduino Uno
  • Replacing the Arduino Uno main microcontroller and bootloader firmware
  • Making voltage measurements using a multimeter
  • Making waveform measurements using an oscilloscope
  • PWM, UART, TWI and SPI signal oscilloscope examples

7.1 Basic Fault Finding and Repair

Some basic fault finding on the Arduino Uno has already been covered in chapter 1. Refer to section 1.5.3 – Basic Testing, for the first things to look for on a faulty Arduino Uno board. Knowing the history of the board can be a big help when fault finding. What happened to cause it to fail? Did it fail while in use, and if so, what was connected to it? If a heavy load was connected to it, a pin on the ATmega328P microcontroller could be burned out, or even the microcontroller itself. If the board was known to be working and then failed the next time it was used, this could point to possible mechanical damage if it was packed away in an unsuitable place, or perhaps damage from static electricity.

Except for the main microcontroller, the crystal for the ATmega16U2 and connectors on an Arduino Uno board, all electronic components are surface mount devices soldered to the top of the board. This makes repair more difficult for the average hobbyist or maker. Some of the bigger devices, such as the 5V regulator, are easier to replace than small devices with fine pitch pin spacing. It is up to each individual to decide whether replacing a part is too difficult or not. Inexperienced users could end up damaging the board more when attempting to do a repair, so discretion is advised.

Replacing the main microcontroller on an Arduino Uno is one of the easier repair jobs to do, which is covered in the next section. In the sections that follow, test points for measuring voltages on an Arduino Uno are shown, which can be used when fault finding in order to determine if voltages at the various points are at the correct levels, or if they indicate a fault.

7.2 Replacing the Main Arduino Uno Microcontroller

Only the Arduino Uno has an easily replaceable microcontroller. The Arduino Uno SMD microcontroller is soldered directly to the top of the board, making it difficult to replace without professional soldering and rework equipment.

If the Arduino Uno main microcontroller is damaged or faulty, replace it with a new device. New microcontrollers are available as blank devices containing no firmware, but some stores offer microcontrollers for the Arduino Uno that have the bootloader firmware already programmed into the Flash memory of these devices.



Chapter 8 • Mechanical Dimensions and Templates

Dimensions of the Arduino Uno as well as positioning and size of its mounting holes are presented in this chapter.

Dimensions are useful when making an Arduino Uno clone board, making a shield to fit an Arduino Uno, when measuring for placing an Arduino project in an enclosure or when drilling a base plate for mounting.

Rather than including all of the dimensions and sizes on a single drawing, they have been spread over several drawings to prevent clutter and for easier reference.

In this Chapter

  • Measurements, tolerance and scale
  • Arduino Uno length, width and mass
  • Arduino Uno and shield dimensions and spacing

8.1 Measurements, Tolerance and Scale

The Arduino Uno board was designed with the Eagle EDA CAD software package using thousands of an inch as the unit of measurement (a thousandth of an inch is also referred to as a mil). Inches are therefore the "official" measurement system of the board. Dimensions in this chapter are given in inches as well as millimeters. All dimensions are subject to manufacturing tolerances so the actual board size may vary slightly from the measurements given.

Images in this chapter are not to scale. Refer to wspublishing.net for an image of the Arduino Uno that can be printed to scale and used as a template for drilling a base plate when mounting an Arduino. Also find Arduino Uno drill templates at the very back of this book after the index.

8.2 Length, Width and Mass

Table 8.1 and Figure 8.1 show the length and width of the Arduino Uno board as well as the overall length when including the USB connector. As the board was designed using inches, millimeter values have been converted from inches and rounded appropriately.

Table 8.1: Arduino Uno Length and Width
Board Length2.7 in68.58 mm rounded to 68.6 mm
Board Width2.1 in53.34 mm rounded to 53.3 mm or 53.4 mm
Overall Length with USB Connector2.95 in75 mm

The size of the Arduino Uno PCB, or printed circuit board, is given as 2.7 inches long by 2.1 inches wide. This works out to 68.58mm long by 53.34mm wide, which is rounded to 68.6mm by 53.3mm or 53.4mm, depending if rounding the width up or down. At the time of writing, the Arduino Uno REV3 web page gave the dimensions as 68.6mm by 53.4mm, rounding the width up.



Appendix A • Specifications Quick Reference

The table that follows contains a summary of the Arduino Uno technical specifications with references to the appropriate sections in this book where more information can be found on each parameter.