From Open Circuits
First, a few definitions:
- a CPU is something that can execute software programs. The earliest CPUs were built out of many parts, but now most CPUs are in microprocessors.
- a microprocessor is a kind of single integrated circuit that includes an entire CPU. In the earliest microprocessors, and some famous kinds of microprocessors still being made, the CPU fills the entire chip, and so require external RAM and ROM/FLASH memory. But now most CPUs sold are in microcontrollers.
- A microcontroller is a kind of microprocessor that, in addition to the CPU, also includes RAM, ROM/FLASH memory, digital I/O, analog to digital convertors, and even comparators on a single die/package.
A microcontroller is a little computer on a single Die/Package. The computer includes a CPU core, RAM, ROM/FLASH, and peripherals including UARTS, A/D converters, SPI, and I2C. Microcontrollers differ from microprocessors in that the microprocessors generally have bigger more powerful central processing units, but need support chips for ram, rom and other peripherals. Most modern microcontrollers use FLASH ram instead of a ROM so they can be programmed over and over. Many modern microcontrollers allow self-flashing to enable bootloading or a firmware update without pulling the chip from the circuit or using a programmer/debugger.
Unlike PCs, which have a wide range of programming languages available, microcontrollers have only a few programming languages available -- C programming language, Basic programming language, Forth programming language, assembly language, and (on a few microcontrollers) Python programming language.
Microcontrollers and microprocessors only understand machine code and compilers regardless of type all translate the program to machine code. Machine code, while tedious to learn and device specific, is the most efficient.
People often have strong opinions about their favorite programming language.
Many hobbyists use microcontrollers, sometimes even multiple microcontrollers, in their projects. Prices have fallen below $5 for the cheapest 32-bit microcontroller and below $1 for the cheapest 8-bit microcontroller.
About 55% of all CPUs sold in the world are 8-bit microcontrollers. Over 2 billion 8-bit microcontrollers were sold in 1997. (Anyone have more up-to-date statistics?)
Somebody always thinks their microcontroller is the best microcontroller, so we have listed all of them as best.
 Microchip PIC
- PIC Links A bunch of links to PIC based information and projects
- Microchip PIC 8 bit FLASH microcontrollers
- Microchip dsPIC/PIC24 16 bit FLASH microcontrollers
- DsPIC30F 5011 Development Board
- Microchip PIC32 32 bit FLASH microcontrollers
- PIC based Demo board
- consider merging the following section to Which PIC to use, to gain the advantages of consolidating information.
Note about choosing a PIC:
The number of PIC models is huge so it is worth saying a few words on how to choose a PIC.
Things to consider as a hobbiest or making a small production run:
- Microchip tends to produce the same chip with minor variations. The exact same chip with the exact same pinout may be available in 8k, 16k, or 32k flash. Spend a few extra pennies and take the best.
- SMT parts take practice to work with, so beginners should focus on DIP package parts with <= 40 pins. On the other hand, SMT parts can yield simpler and smaller PCB designs so they are worth consideration even for a hobbiest.
- Contrary to common sense, older parts are often more expensive then newer parts.
- Consider if a free/student version of a C compiler is availible. Microchip provides free/student student versions for the 18f,dsPIC/PIC24, and PIC32.
List of some of the best PICs for hobby purposes:
|PIC||Pin Count||Important Features||Typical Use|
|PIC12F683||8||ADC, I/O PWM, Comparator||Very Simple Projects/Glue Logic|
|PIC16F88||18||ADC, I/O PWM, Comparator, UART, I2C/SPI||General Purpose|
|18F2620||28||ADC, I/O PWM, Comparator, UART, I2C/SPI||General Purpose|
|18F4620||40||ADC, I/O PWM, Comparator, UART, I2C/SPI, 8 Bit Parallel Port||General Purpose|
|18F2550/18F2553||28||ADC, I/O PWM, Comparator, UART, I2C/SPI, USB||USB Connectivity|
|18F4550/18F4553||40||ADC, I/O PWM, Comparator, UART, I2C/SPI, USB, 8 Bit Parallel Port||USB Connectivity|
|P24FJ64GA002||28||ADC, I/O PWM, Comparator (with software selectable pin assignment), 2 UART, 2 I2C, 2 SPI||General Purpose|
Note: J means the PIC is a native 3.3V part. Other PICs will run at 3.3V but only at slower clock speeds.
 Atmel AVR
The AVR series is split into 4 different types:
|ATtiny||Small (2 Ports or less) 8 bit RISC PU but extremely powerful (20MHz System Clock, 20MIPS, 64MHz Fast Peripheral Clock)||ATtiny25/45/85, ATtiny 26/46/86, ...||10bit ADCs, USI, 8/16bit timer, PWM, I²C, SPI , BOD, WDT, ...|
|ATmega||Powerful 8bit RISC PU with up to 10 IO Ports and up to 256k flash (20MHz system clock, 20 MIPS)||ATmega88, ATmega16/32, ATmega640/1280/2560, ATmega1281/2561, ...||10bit ADCs, USARTs, 8/16bit timer, I²C, SPI, BOD, WDT, ...|
|ATxmega||Extremely powerful 8/16bit RISC CPU with up to 10 IO Ports and up to 256k flash (32 MHz system clock, 32 MIPS)||ATxmega64A1/128A1/192A1/256A1, ATxmega64A3/128A3/192A3/256A3, ....||12bit ADC, 12bit DAC, 16 bit timer, USARTs, SPI, I²C, DMA, Real time clock, crypto engine,..|
|AVR32||High End 32bit RISC CPU for multimedia purposes (system clocks up to 200 MHz and more)||AP7000, AP7001, AP7002, AT32UC3A0128/0256/0512, ...||A lot =), see atmel.com for futher details|
Especially the ATmega series is very easy to use and is the best processor for beginners. All small chips are available in the easy to use DIL package and combined with an AVRDragon for about 60€ everybody with a budget of about 70€ is able to build and debug his own microprocessor applications. The AVRDragon allows you to debug all ATmega & ATtiny processors with less than 32k flash using DebugWire or JTAG and to program all ATmega / ATtiny devices using HVPP, ISP and JTAG.
- Arduino Links Arduino is a development board based on AVR Microcontrollers
- Atmel AVR 8 bit FLASH microcontrollers
- Atmel ATmega & ATtiny
- Atmel ATxmega
- Atmel AVR 32
- Simplest AVR programmer Using LPT Port
 Development Boards
Development Boards are printed circuit boards that contain a microcontroller and enough circuitry to get it going, typically at least some of the following: clock, voltage regulator, reset button, communications chip, buffer amplifiers, led's, prototyping area, and/or off chip connections. Sometimes the manufacturer of the chip sells development boards ( often called evaluation boards ). Development boards can be really basic, just enough to make the processor run, with connections to the IO pins. Or the boards can include communications, displays, input buttons etc. Often you can jump start a project by using a development board that does the boring standard stuff and let you focus on your project. The development board can let you use high density parts and surface mount parts that you might not want to mess with. The BitWacker kit from SparkFun is priced close the to the total price of the parts. This is probably true of some other development boards as well. Note that some development boards require you to build them they have not been made available as kits, some come both ways.
- Chalk Roach based on AVR Atmega32
- Arduino Links Arduino is based on AVR Microcontrollers
- USB Bit Whacker This is a PIC 18 based system ... can be used with BitWacker Java Communications
- RS232 Dev Board
- dsPIC30F 5011 Development Board
- GoGo Board based on PIC18F4550 (via Prof. Paulo Blikstein): "an open-source platform that is designed to be low-cost and allow for local assembly by those who are interested." All parts are through-hole (even the USB connector). KiCAD PCB design files.
Other demo boards: see demo board.
 Cypress PSoC
- Cypress PSoC 8 bit FLASH microcontrollers.
- Wikibooks: Cypress PSoC
- SparkFun: Gainer PSoC Development Board including USB interface -- looks very similar to the Arduino Nano
- LPC2103 Low cost 70MHz ARM7TDMI-S FLASH Microcontroller from Philips. The "$49" "Coridium ARMmite" does use this chip.
- the ARM microcontroller wiki.
There are no ARM chips currently manufactured in a through-hole package -- they are *all* surface-mount. However, there are many "adapter boards" aka demo board that make them easier to use, such as:
- low-cost ARM demo boards at NGX Technologies: 
- $10 STMicroelectronics’ STM32 Discovery Kit with ARM® Cortex-M3 microcontroller  
- Motherboards that run Linux
 further reading
- Instructables: How to choose a MicroController
- Wikibooks: brief selection guide
- veys.com microcontrollers May have been a one man effort, now dropped. Has a bit of content that looks good.
- Cornell University ECE 4760 Designing with Microcontrollers Final Projects A ton on projects.
- Which uC (Microcontroller)? - discussion
- PIC vs. AVR Ultimate fight
- Chiphacker: "What’s the difference between a microcontroller and a microprocessor?"