Arduino boards such as the Uno R3 are microcontrollers that can be used to create interactive objects.  Sensors and actuators of an almost bewildering variety are available or can be readily constructed.   Arduinos are at the forefront of the “open hardware” movement, comparable to the “open source” software movement.

Arduino “shields” are add-on boards that extend functionality or provide a means of breadboarding.  Shields are available for various communications (wired and wireless Ethernet, GSM, Xbee modules, serial/USB, Bluetooth), motor and lighting control, and other extensions.

Programming Arduino boards is easy.  The language used for most development is a kind of “baby C” combined with very simple APIs.  Arduino core software and most libraries are licensed under LGPL and the development software is GPL (no problem for deployment of commercial applications).

The Arduino Uno Rev 3 costs approximately $30.  It contains an ATmega328, an 8 bit RISC processor delivering up to 20MIPS and having on chip 32Kb of flash memory, 1Kb of EEPROP, and 2kb RAM. The ATmega328 has many I/O features for both analog and digital sense and control.

The Arduino Uno R3 board is pictured below in approximate actual size. Note the USB connector on the top left which may be used to power the unit as well as communicate.  A separate power connector is provided, visible on the bottom left.

Other models of Arduino are available that have different I/O configurations; All are inexpensive, reliable, and may be considered for building cheap and reliable sensor and actuator systems.