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Ask HN: Why don't microwave ovens have IR cameras to tell when food is done?

7 points by crazygringo ↗ HN
I use my microwave all the time -- to reheat frozen cooked salmon (ideally to precisely 130°F), to heat up leftover soup from the fridge (ideally to more like 170°F), or to boil water for tea (faster than stove or electric kettle in the US).

And to cook foods without overcooking requires low power settings (~20%) for long periods of time (6-15 min), but constantly checking the temperature, guesstimating another x minutes, rinse and repeat... there has to be a better way!

It seems like building a cheap low-res IR camera in the roof of the microwave would be such an obvious idea. I punch in my desired 130°F, and it alternates between heating and waiting -- as soon as it detects hot spots or any food that's reached the target temperature, it backs off, then starts up again until the whole item is at desired temperature. Your food is never overcooked, and never undercooked. You could even defrost perfectly, and/or hold a temperature for really large items to penetrate the inside.

Yet there seems to be vanishingly little progress. Searching online yields 2015 patent that seemed to go nowhere [1], a dismissive article from 2018 [2] about a hard-to-use IR accessory, and a deep learning paper from last year [3].

So I thought I'd ask here, since there are bound to be engineers with experience. Is there something I'm missing here that either makes it impossible to build (e.g. microwaves would fry the camera electronics or something) or somehow so inaccurate it wouldn't be worth it?

I don't know if this is a startup idea, or just something I wish the big brands would start producing...

[1] https://gizmodo.com/infrared-microwave-lets-you-watch-your-food-change-colo-1685143405

[2] https://www.theverge.com/2018/3/19/17139114/cmicro-microwave-temperature-sensor-system-kickstarter

[3] https://www.mdpi.com/2571-5577/3/1/13/htm

9 comments

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OJFord
Interesting idea. It's just cost I reckon. Microwaves and ovens are relatively cheap, and yet still have massive markup.

Thermal imaging at the level you'd want for this (you don't want to just read a hotspot and declare it hot enough) is more expensive than many microwaves.

allears
Surface temperature may vary widely from internal temperature. Also, if an IR camera is to detect hot spots, you'd need some intelligence to analyze the image. Sounds like the development of such a gadget wouldn't be so simple.
crazygringo
Thanks. You'd absolutely need to digitally process the image, so it's absolutely not as simple as just hooking up a sensor, but it seems like a basic chip should be able to handle it. It's really ultimately just some basic statistical processing of a histogram of temperatures I think.

And I don't think surface temperature is a problem -- I read a source (can't find it now) which claimed that once the entire outer temperature of something in the microwave has reached the desired level (no cold spots), that's the moment that the inside has too. I'm not sure if that's accurate, but simply "holding" the surface temperature there for a couple or a few minutes would seem to solve that as heat penetrates from conduction, I think?

Someone
Is it possible to reliably measure the temperature inside a food item from an IR camera picture showing one side of the food item?

I guess you would need to know/estimate quite a bit about the food stuffs’s composition, volume and thermal conductivity to do that.

Also, what you describe, to me, is heating, not cooking. Cooking is more than “bring it to a given temperature”; it involves chemistry that needs time to do its work, and that time varies by product (with natural products even across ‘identical’ products)

I think, at best, this would only work for heating.

crazygringo
Yes, this is specifically for (re)heating -- but that's also all I thought people really did with microwaves?

I do a lot of cooking, but I'll confess I've certainly never "cooked" something in the microwave. If something needs anything else -- browning or frying -- I'm not expecting my microwave to take care of it. :) Nor will I be braising a cut of meat in there for hours....

[dead] buffaloo
Just Google “microwave thermometer.” It’s a $10 gadget you leave in the food while you microwave. No AI required.
2rsf
Some microwave ovens actually have a temperature sensor that you can stick into your food,it seems to be more cost effective than an IR camera
dTal
A "cheap low-res IR camera" isn't really a thing. Thermal imaging cameras cost a lot more than your average microwave, even at resolutions we would consider "super low" by visual standards. The only way it would be worth it is if it worked flawlessly, which it probably wouldn't even with a pile of R&D. Microwaves intrinsically never heat food evenly, so in order to heat the whole system to your desired temperature, you must perforce heat parts of it to above your desired temperature, or switch the magnetron on and off an excessive number of times as the system asymptotes. Nor are the hotspots in a random place, but are fixed resonances; the best we've been able to do about that is a turntable, which turns a hot spot into a hot radius. So you're going to be heating the same spot multiple times. Microwaves are just unsuited for this, and a thermal camera won't help much.

For your poaching salmon application, you probably want a souse vide bath. You can build a passable one for pretty cheap - it's just a pot of water on a hot plate and a thermocouple. It will heat the entire surface of the food to exactly the target temperature and hold it there; you can detect when the food is up to temperature by measuring how much energy you need to maintain the bath.

To boil water in the microwave, may I suggest a sealed container with a plastic whistle, like a kettle?