At InfoAge Science Center in Wall, New Jersey. (Formerly Camp Evans)

Introduction to Microcontrollers

What could *YOU* make with a $1 computer?  A computerized light show?  An autonomous astromech droid?  A vintage video game console? A flying drone?  Let's find out! 
Links to External Resources 

What is a Micro-controller?

A microcontroller (abbreviated μC or MCU) is essentially an entire computer system on a single, tiny microchip!  While not as fast or powerful as your desktop or laptop computer, a microcontroller excels at being very small, very inexpensive, and can operate on very little power (great for battery-powered devices).
Microcontrollers are the heart of what's called "Embedded Computing" - a term used to describe using these tiny computers inside everyday things to make them "smart" - things like microwaves, cars, cellphones, TVs, and so on. 
A microcontroller has many subsystems on board it's tiny little chip.  The central part is the microprocessor core - it's the brain of the computer that carries out program instructions.  Other subsystems include: 
  • RAM (Random Access Memory) - where the software can store data temporarily.  This memory is lost when the power is turned off, so it's usually used to store information that the program generates as it runs through it's instructions.
  • Flash memory - where the software program is stored.  This memory is not lost when the power goes off.  It is similar to the SD card in your smartphone or digital camera.
  • EEPROM (Electroniclly Eraseable Programmable Read Only Memory) - a special type of memory that can retain data after the power is turned off.  This is a good place to store things like configuration settings, that need to be remembered for next time the system is powered up.  It only stores data, not program code.
  • IO (Input/Output) Systems - this is how the microcontroller communicates with the outside world.  There's many different types of I/O, such as digital (1s and 0s), analog (variable voltage), PWM (Pulse Width Modulation) which falls somewhere between digital and analog, and many types of computer protocols like Serial, I2C, Parallel, CAN, 2WI, and more.
You don't need to worry about all these just yet.  As we start to look into different brands and variations of microcontrollers, you'll notice that the reason there are so many different microcontroller choices is that they all come packaged with different combinations of subsystems, or are made to run with different power requirements or at different speeds. 

What's an Arduino?  Isn't that a Microcontroller?

An excellent question!  Many people have heard about the Arduino (pronounced arr-duee-no) and may have heard them called a microcontroller, but actually, Arduinos encompass much more than that. 
The Arduino is a full development system, or prototyping system.  It includes a complete circuit board and support hardware to help make using the microcontroller easier.  Some things that the Arduino provides to help you out:
  • Voltage regulators: help provide clean, stable power.
  • Timing oscillators: There is a 16MHz quartz crystal oscillator to give the USB controller an accurate, stable time base; and a 16MHz ceramic oscillator for the main microcontroller clock.
  • USB interface: allows you to plug the Arduino into your PC to download your programs.  It can also provide power to the Arduino.  Includes the USB connector, a USB controller (which is a separate microcontroller), transmit/receive status LEDs, and the 16MHz timing crystal.
  • Power Plug - to plug into a wall adapter for power.
  • Reset switch, and a test output LED:  Convenient items to include on a prototyping board.
  • Stackable "headers": these rows of connectors make it easy to plug in additional add-on daughter boards (called "Shields").  These allow you to easily expand and customize the features of the Arduino.
This is the Arduino "Uno":
Arduino Uno
Arduino UNO

This is the microcontroller used in the Arduino "Uno":
ATmega328p
Atmel ATmega328p
Arduino IDE
The Arduino IDE (click to enlarge)
 

Arduino doesn't stop with just the hardware, though.  There is also the Arduino integrated development environment (IDE) that runs on your desktop computer.  This is where you write the program that becomes the instruction code that runs on the microcontroller.  The Arduino IDE helps to make all these tasks very simple.
Arduino was designed to be used by beginners and people who are new to the world of microcontrollers - such as students, teachers, amateurs, and hobbyists.  This has made it a great place to start for many people! 

For More Arduino Information

Make Magazine's "An Introduction to the Arduino":
External Links:

Popular Atmel AVR Microcontrollers

Atmel has hundreds of different variations of their AVR microprocessors, even though they all have (mostly) the same microprocessor core.  To help narrow the focus, here we discuss a couple of their most popular chips.
These microcontrollers are popular with hobbyists and DIYers because they are cheap, versatile, easy to use, and most importantly - available in DIP packages!  They are all based on the same processor core: an 8-bit AVR.  The two main categories are the lightweight Atmel tinyAVR (ATtiny), and it's big brother, the Atmel megaAVR (ATmega).  For the adventurous, Atmel also has the XMEGA line, with way more X factor, but these are not available in DIP packages.

Here's a comparison on some of the more popular versions:
Image MCU DIP Size Used in Flash RAM EEPROM Distributors Approx. Cost
ATtiny13A ATtiny13A 8-pin "tinyCylon", "Lux Spectralis" 1 KB 64 B 64 B Mouser $.94
image ATtiny85V 8-pin "TV-B-Gone" 8 KB 512 B 512 B Mouser $1.62
image ATtiny2313A 28-pin "USBtinyISP AVR Programmer" 2 KB 128 B 128 B Mouser $.94
image ATmega168 28-pin "Arduino Duemilanove" (old version Arduino)
"Ice Tube Clock"		 16 KB 1 KB 512 B Mouser $3.11
image ATmega328P 28-pin "Arduino UNO"
"MONOCHRON Clock"		 32 KB 2 KB 1 KB Mouser $2.50


Are all microcontrollers from Atmel?

No way!  There are LOTS of microcontroller families out there, so many it can be hard to choose!  Here are a few more families that are favorites in the hobbyist community that you may be likely to come across:

Parallax BASIC Stamp

Basic Stamps
Board Cost: $29-$89;  Features vary

The Parallax BASIC stamp is similar to an Arduino in that is it a whole development board, with all the support electronics taken care of for you. Just plug it in and you're ready to go!

The BASIC Stamp was designed specifically to make learning about microcontrollers simple and easy.  You program the BASIC stamp using the BASIC programming language.  The microcontroller runs a BASIC interpreter on board, so all you need to do is load your BASIC code onto the chip to have it run - no compiling needed!

Spin and Java language version are also available.

Parallax Propeller

Picture
Chip Cost: $8 
Features:
  • 32-bit architecture
  • 8 processor cores (cogs)
  • RAM/ROM: 32 KB/32 KB
  • Speed: up to 80 mHz
The Parallax Propeller is a mighty powerhouse of processing power - it has 8 processor cores!  Called "cogs", these multiple cores allow you to multiple things at the same time (multitask).  Propellers are being used to make video games systems (like the Hydra), used in robotics, and are capable of producing very nice voice synthesis.

The primary programming language for the Propeller is called "Spin", and there are many other options available.

Microchip PIC

Picture

ARM-processor based 

BeagleBone
The 32-bit ARM processor is becoming increasingly popular in low cost development boards.  It's powerful enough to run a LINUX kernel, giving you PC-like power in a tiny form factor.  ARM processors are used in many smartphone and tablet devices.  While we won't go into a full discussion of ARM architecture at this point, here are some popular ARM-based development boards to watch:
IXR - The Institute for Exploratory Research