So here's two crack-pot ideas I just had. I haven't crunched the numbers or considered how to do a full implementation of it either. Now as we all know the changes in resistance of nichrome or kanthal wire are very small even at high temperatures.
So run with me, come up with a way to refute these, or come up with other ones?
Both operate under the assumption that we know the resistance of the coil at rest. Which is easy to obtain and almost all regulated devices are doing this already.
Here's the real crack pot idea...
1) Say we put a hall effect sensor underneath (or as a ring around) the atomizer to measure the magnetic field of the coil. Keep in mind, these coils we're using are basically solenoids. The magnetic flux would be proportional (probably not linearly hahaha) to the temperature of the coil and could be used to cross of the variables relating to how much power is being sent to the coil verses how much is flying through (IE: creating a magnetic field). Knowing the power being supplied to the coil would help a good deal as well.
I used a little app on my cellphone which serves as a crude magnetometer, and when I fire my atomizer at 15 watts I get a shift of about 4 microtesla being about half a cm from the atomizer. I imagine the field change could be as drastic as 10microtesla and read to two decimals of accuracy under better conditions.
2) Say the user selects what gauge wire to use from a menu for Kanthal (standard material right?). The chip can quickly calculate approximately how many wraps there are at rest, or even ask if it's unsure "2.5mm 7 wraps?" (IE Steam calculator). Why couldn't a mod interpolate the temperature of the coil from the power applied over time? Sure it wouldn't be perfect and values would have to be stored under certain conditions. Imperfect coils with super long leads could create hot-spots as well. Even if it didn't give the supposed +/-1 degree accuracy which nickel wire can, isn't +/-5 degrees "good enough" to prevent whick from charring when dry?
I'm not a fan of drilling through atomizers to put IR thermometers in place or whatever, seems finicky.
1: since the magnetic field is just going to be a function of the current, measuring the magnetic field won't help; the mod already knows enough to figure out the current anyway.
2: Being able tell the mod what wire gauge etc could be usefull for the mod to make a best guess / recommended operation / vape profile.