Why can't this be done in firmware, like Weller does?
An idle station is detected by monitoring heat demand, which is steady and low when the iron is in the stand. Once you solder, heat demand increases and it resets the timer. It works good.
It works OK, but not
great. My Ersa i-Con nano uses that approach, so I’m familiar with it. Two issues:
1. It doesn’t allow for really short setback timers (like 10 seconds) because it could go into setback while in your hand, e.g. while preparing a joint.
2. The bigger issue: Once the iron has gone down to the setback temperature, it relies on detecting a plunge in temperature (from wiping on the brass wool or sponge) to figure out that you want to solder again. So far so good. But where it gets problematic is when it’s just entered setback mode and the iron temperature is falling. If you grab the iron and wipe it on the brass wool to drop the temp, it doesn’t wake up, because it’s
expecting the temperature to drop at that moment. So there’s a, say, 20-30 second window during which it won’t resume from setback automatically. And as it happens, it’s often right when you’ve finished inserting a bunch of components or dressing wires or whatever.
The “big” i-Con stations use an accelerometer in the handle to much more accurately detect activity.
IMHO, some kind of mechanical sensor, be it in the handle or in the stand, is the way to go.