How do 'flex zone' induction hobs work? - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 22, 2021, 01:43:04 pm
content: So, I'm renovating the house, one of the things I'm doing is buying new kitchen hardware. I always enjoy seeing how much (or lack thereof) advancements have been made in kitchen appliences over the last decade; but found myself pleasantly surprised.A number of (usually more higher-end) brands have fully 'flex' induction hobs. Instead of having circles where you put your pan, you can put the pan wherever you want, it will detect this location and magically only heat here. How does this work? Take for example this Miele hob:https://www.miele.be/nl/c/kookplaten-en-combisets-2473.htm?mat=11754180&name=KM_7697_FLHow does it work? I suspect lots of tiny induction coils in a honey-comb pattern or something? Anyone have teardown/experience inside?

author: langwadt
author_rank: Super Contributor
timestamp: May 22, 2021, 02:09:23 pm
content: https://www.bamohobs.com/wp-content/uploads/2018/03/free-zone-induction-cooktop-hob-740x444.png

author: coppice
author_rank: Super Contributor
timestamp: May 22, 2021, 03:49:33 pm
content: Quote from: langwadt on May 22, 2021, 02:09:23 pmIts easy to guess that this image is what they look like inside. Detecting where a pot is present isn't hard. What is more interesting is how they detect which pot is where, so you can gently keep one pot warm, while aggressively heating another pot.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 22, 2021, 04:30:17 pm
content: I can envision a UI that makes it pretty obvious -- the impedance of each coil is sensed and presented graphically with some processing. Edge and group detection to define objects, then you can just for example poke whichever area is active and select its power level (or temperature if that's a feature, or etc.). And the regions track from scan to scan, so if you slide some pots around, they don't fuck up too badly. Maybe even if you remove and return a pot, it could remember the shape and size and recall the setting, though it's probably as dangerous as it is useful to do that, better to just leave it off until the user says otherwise?...How they expect to put that into that panel of numbers, I have no fucking clue?As for the nuts and bolts, easy enough to scan each coil for impedance and go from there. Trickier once some are operating, interference is a given here. It could be heavily filtered, with orthogonal frequencies on adjacent coils say. It's probably not TDM as the ratio of peak to average power would have to be huge, and I know they tend to go with that already ("quarter bridge" 1-wave pulse) but that much dead time between pulses would be painful. Or, maybe they stop everything and do a detect scan once in a while, it's not like it has to be done every cycle, yeah.Also, I wonder if they have to do low level scanning, to comply with EMI, or idle current or whatever? I don't know what standards apply to those things.Tim

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 22, 2021, 05:23:41 pm
content: Quote from: T3sl4co1l on May 22, 2021, 04:30:17 pmI've noticed that most brands advertise being able to deal with 6 different cooking pots, but miele (at a significantly higher cost) can do 8. I wonder if this is just a 'choice' of interface, or has to do with to do with something more technical (orthogonal tones used in scanning or something?)

author: coppice
author_rank: Super Contributor
timestamp: May 22, 2021, 05:47:51 pm
content: Quote from: TheUnnamedNewbie on May 22, 2021, 05:23:41 pmIts probably just a marketing move. You can't get more than 6 pots on most of these things, so the engineers have no practical reason to distinguish more than 6 zones..... but the marketing people do, if 6 is the norm. Its like making a touch surface support 11 finger multi-touch.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: May 22, 2021, 11:00:07 pm
content: Quote from: coppice on May 22, 2021, 05:47:51 pmThat wasn't a finger.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 23, 2021, 11:41:33 am
content: ( ͡° ͜ʖ ͡°)