The SMD soldering iron is an adjustable station for 12V 7W Stannol soldering irons. These are espacially for SMD parts because of their small tip.
This module was created for the (more or less accurate) temperature control. The temperature is controlled by the linear voltage regulator LM317. The LM3914, a bar display driver, is converting the analog voltage to a bargraph display. R8 is for calibrating the display. K6 and K7 are for the soldering iron and S1 is the power switch for enabling and disabling. R1 is for setting the voltage and D3 is just so you can see if the iron is on or off.
Thats it, here are schematic and some pictures.