How to add temperature control to a soldering iron

I see lots and lots of builds of "temperature controlled iron" that simply either:

• adds a timer to an uncontrolled iron


• adds a dimmer to an uncontrolled iron

The first is the same as turning on the iron later. And the second is the same as paying too much for a 25W iron (because that's what your 75W iron will become).

Are there any projects out there really adding closed loop temperature control to an unregulated soldering iron?

I think this can be done way cheaper than buying an overpriced Weller, but before I start something I would like to see where others failed/succeed and I'm failing miserably in finding any preceding work on this.

Answer

For an automatic temperature control, you would need three basic components:

1. A way to sense the temperature of the iron at the tip



2. A way to control the power supply to vary the temperature


3. A microcontroller to read the temperature and determine how to adjust the power supply to achieve the desired temperature

Since you asked for preceding work here is a nice build log of a DIY mod to a soldering station including a lot of nice pictures, schematics, and firmware.

And Dangerous Prototypes looks to be putting together a kit of some sort. But some of the links are dead and information is missing. But they do have a nice custom PCB for the project that is currently out of stock as of this writing. I'm not sure if this is a work in progress or just an unfinished and forgotten about project. You could probably email them and ask for an update.

PS: I agree with AndrejaKo's assessment on the dimmer controlled iron. For some people, that's all they want'need. Here is a nice Instuctable on how to do just that.