Mike over at PCBSmoke has written an article detailing the build of his digital temperature controlled soldering station:
The unit uses a PID temperature controller, an SSR (Solid State Relay) and a transformer plus a metal enclosure case, a soldering stand and a few other parts. It is relatively inexpensive to build, plus it makes a pretty good shop tool.
This homemade unit is not as responsive as one of the commercially manufactured ones like a Weller or a Hakko, but it works surprisingly good. The PID controller was designed primarily for manufacturing process control, but it was easy enough to adapt it for use in a soldering station. Accompanying this post is a series of videos showing how to optimize the PID controller and get the best performance from it.
Check out the video after the break.