See also the Platino Soldering Station for more discussions about this project.
The project is about a cheap SMD solder station built as an Arduino shield (Arduino UNO). It supports active soldering tips from Weller (RT series) which contain the heating element as well as a sensor and provides a standard 3.5 mm jack. Together with the corresponding female connector you will get a compact SMD soldering iron with very fast heat up times of a few seconds. The shield consists of a low-noise amplifier for measuring the temperature via the ADC of the AVR, a power MOSFET stage to control the heating using PWM and a 7-segment LED display and push buttons for setting and displaying the temperature. The controller is realized digitally on the AVR. Further information can be found at: http://www.martin-kumm.de/smd_solder_station