LWN: Comments on "A Linux-powered microwave oven"

Partial-power microwave oven

pr1268 — Sat, 20 Feb 2016 22:46:10 +0000

Dammit, Jim, I'm a computer scientist, not an electrical engineer with a background in microwave propagation effects! ;-)

Of course, my "invention" was just a thought-concept; the scenario you just described succinctly (and graphically) describes why such a microwave oven has not been introduced.

Cavity resonators would add mass and size and no doubt reduce efficiency by producing still more heat.

Like I said, for n extra parts, O(n^1.5) complexity...

A sincere thank you for enlightening me. :-)

A Linux-powered microwave oven

Wol — Fri, 19 Feb 2016 18:37:18 +0000

My mum actually inherited her microwave from me :-)

And both hers and mine have various features I would NOT want to lose. Namely heating elements at the top (commonly known as "a grill"), and at the back (commonly known as a "fan oven").

Our kitchen now has a conventional oven and a combi-oven built-in, and the combination is great. Incidentally, for those who think AU$1K is expensive, if I could get a built-in combi for that price I would consider it very good value for money.

The one big problem with our new - analog - combi is we have to remember to check the settings each time we use it. My old - digital - oven reset itself back to its defaults after every use. It also had the ability to set several programs to run consecutively - made superb baked tatties - set it for 10 mins on combi followed by 10 mins on fan oven and one lovely tatty. Our new analog you have to do the first setting, then when it bleeps "finished" you need to go back and reset it for the second setting.

Cheers,
Wol

A Linux-powered microwave oven

dfsmith — Fri, 19 Feb 2016 00:23:54 +0000

I don't think I'd trust my fridge with my credit card. It would probably blow all my money on milk and eggs and look sheepish when I couldn't close the door.

A Linux-powered microwave oven

spaetz — Thu, 18 Feb 2016 14:29:18 +0000

> I can't even begin to imagine any possible purpose for a fridge being able to access a Google calendar.

Easy, so it can order champagne when you have planned your next orgy. SCNR

A Linux-powered microwave oven

nye — Thu, 18 Feb 2016 12:54:42 +0000

I guess I'm becoming an old man: I can't even begin to imagine any possible purpose for a fridge being able to access a Google calendar.

Partial-power microwave oven

opalmirror — Wed, 17 Feb 2016 23:58:51 +0000

So here you have two magnetrons relatively tightly coupled, resonant at approximately the same frequency, one powered and one unpowered. To me it seems the unpowered magnetron acts as an ideal resonant antenna to receive RF power from the powered magnetron. Even if the unpowered magnetron is connected to an open circuit, I'd expect significant currents and waste heat generation. If both magnetrons are powered and coherent (same frequency), then synchronization of their output might be tricky - they would have to be in the same phase, or they would be exchanging a lot of power one to the other. The fact one is twice the power of the second could mean the large magnetron may burn up the smaller magnetron or send current back into its power supply. Maybe you could detune them (different frequencies) and/or use a cavity resonator as a narrow pass filter so that one magnetron isn't very much affected by the other. Cavity resonators would add mass and size and no doubt reduce efficiency by producing still more heat. Just thinking...

A Linux-powered microwave oven

sdalley — Tue, 16 Feb 2016 16:18:31 +0000

Hmm. My snazzy Panasonic microwave inverter power supply went phut after 18 months. PSU not replaceable. Whole oven now pushing up the landfill.

Went back to a more straightforward on-off microwave, which is is still going fine after 3 years.

KISS, indeed.

A Linux-powered microwave oven

ortalo — Mon, 15 Feb 2016 14:15:30 +0000

Forgetting adequate security mechanisms in embedded systems and devices may reveal real dangers in my opinion.
Please, do not forget to include an instance of a decent security kernel able to *prohibit* the development and installation of and computer game on the oven touch screen interface, especially those of the variety involving throwing distinguised species of volatiles or mammals onto each others and their baricades.
If you fail that, your loved one and yourself will lament all day on the unavailability of all the kitchen devices and the incredible overheads added to all day to day operations around breakfast, lunch, dinner - due to preemption by your own (little) loved ones.

turntable vs microwave scatterer in oven

giraffedata — Mon, 15 Feb 2016 00:11:29 +0000

I read once that the stirrer is fully effective and the only reason for the turntable is that it seems to customers to be helpful.

That makes some sense. Customers are acutely aware of uneven heating problems in microwaves, so will pay more for something that seems to address that. But that uneven heating is actually caused by uneven composition of the food, so the turntable doesn't help.

A Linux-powered microwave oven

raven667 — Sun, 14 Feb 2016 02:51:14 +0000

That never occurred to me before but that makes a ton of sense, that also kind of tracks with the shows these ads run on

A Linux-powered microwave oven

mathstuf — Sat, 13 Feb 2016 23:35:26 +0000

> There is also a lot of advertising out there to convince people that every chore is just _too_hard_ and you need a much larger number of appliances than are really necessary.

Those "As Seen on TV" bits should be viewed in light of being targeted at those with disabilities or handicaps. The reason they show normal people purposefully failing is because someone with Parkinson's failing to cleanly break an egg is not something anyone wants to tape, be taped doing, or watch.

A Linux-powered microwave oven

flussence — Sat, 13 Feb 2016 16:05:45 +0000

Thanks, I learned something new today. That explains why things instruct you to thoroughly defrost them using conventional methods before microwaving; the still-frozen parts will never be heated up. (I had an unfortunate experience once that corroborates this)

A Linux-powered microwave oven

lbt — Sat, 13 Feb 2016 09:44:44 +0000

Put a sensor under each foot (ie between the rubber foot and the frame) similar to the Wii balance board.

Trivial to calibrate and recalibrate too.

Partial-power microwave oven

pr1268 — Sat, 13 Feb 2016 07:45:47 +0000

Not quite. The Panasonic "inverter" ovens (and their licensees) do a credible job of running at partial power.

Interesting... I was thinking of inventing a microwave oven with two independently-controlled magnetrons, each with a different thermal power rating (e.g. 400W and 700W). Any combination of running either/both could give three different heating states (approx. 1/3, 2/3, and full power). Running one continuously and the other toggling on/off (partial load) could give even more discrete power levels.

Of course, there's the unwritten postulate that the complexity of mechanical devices with n parts is O(n^1.5). Or thereabouts. Adding another magnetron would make the microwave oven unnecessarily more complicated. Oh, well...

A Linux-powered microwave oven

luto — Sat, 13 Feb 2016 05:13:23 +0000

> an on/off switch for the magnetron (since it only has two working states: full-power and off).

Not quite. The Panasonic "inverter" ovens (and their licensees) do a credible job of running at partial power.

The toaster story actually there's another toaster story, sort of

pr1268 — Sat, 13 Feb 2016 04:54:45 +0000

I thought you might be referring to this story, which also discusses two types of toasters. Perhaps the $20 toaster Donald Norman reminisces about is the model the king's electrical engineer whipped up, while the ₩250,000 model is the one for which the computer scientist was beheaded. ;-)

Apparently, there's a big market for appliances (well, software, too) that have complex, extraneous, and (generally) unneeded whiz-bang features. At least in Korea, where having a refrigerator with a control panel that looks like a nuclear power plant control room is a status symbol.

A Linux-powered microwave oven

boog — Fri, 12 Feb 2016 20:32:13 +0000

Another problem is that hot water absorbs microwaves better than cold, so small initial variations in temperature tend to run away.

A Linux-powered microwave oven

bronson — Fri, 12 Feb 2016 19:17:50 +0000

Supporting evidence: fridges bought a few years ago are already obsolete: https://productforums.google.com/forum/#!topic/calendar/U...

Now that's progress!

A Linux-powered microwave oven

rgmoore — Fri, 12 Feb 2016 19:14:42 +0000

I actually find that for many appliances, they really peaked in the 1950s and the actual utility has been on a plateau or decline since then.

I'm not sure I'd go that far, but I agree that development is very slow, especially compared to anything involving computers. The key is that for anything, the biggest change is from having nothing to having something, and after that it's mostly refinement, and often with declining returns. An icebox is a huge improvement over nothing, a refrigerator is a big advance over an icebox, but after that you're chasing improvements in convenience and efficiency rather than basic function. Similarly, many of the changes to the microwave (e.g. turntable for the food, variable power level) are real improvements, but they're marginal advances compared to getting one in the first place.

A Linux-powered microwave oven

bronson — Fri, 12 Feb 2016 19:13:19 +0000

The stirrer is cheaper than a rotating turntable (just a stamped piece of cheap sheet metal and a tiny motor) but it's also less effective.

Don't most microwaves have both? Just looked, our crappy Frigidaire has both. Sample size of 1.

A Linux-powered microwave oven

bronson — Fri, 12 Feb 2016 19:05:55 +0000

Microwaves already have stirrers: http://ffden-2.phys.uaf.edu/104_spring2004.web.dir/arts_m...

It's about as good as you can reasonably get... If microwaves were spherical and had multiple entry horns (not sure the correct term) then they could cook a little better but, of course, they'd be much harder to package and produce. And there would still be hot and cold spots -- uneven heating is as much a feature of the food as the oven.

Maybe one day we'll have variable-frequency phased array microwaves that use feedback to direct heat right to the cool spots. (dibs on the patent!)

A Linux-powered microwave oven

rgmoore — Fri, 12 Feb 2016 19:02:46 +0000

A lot of home appliances have come to a state where it would take some serious engineering to make a substantial improvement over previous models (which is expensive), so to keep up a fake air of technological evolution (as we've come to expect it from other devices such as computers or phones), they just tack things on that makes them look more advanced than it really is.

Pretty much. Most of them are relatively simple mechanical tools for performing mechanical tasks- chopping, mixing, blending, etc.- so that there isn't a huge amount to change. They seem to do a few basic things- changing cosmetics, expanding the product line to larger or smaller models, making the motor more powerful, or just trying to squeeze out production costs- that don't change the basic functions. There is some genuine innovation out there- I've been amazingly happy with my induction range, which is a huge advance over conventional electric stoves- but it happens much slower than in tech.

A Linux-powered microwave oven

raven667 — Fri, 12 Feb 2016 17:02:17 +0000

> A lot of home appliances have come to a state where it would take some serious engineering to make a substantial improvement over previous models (which is expensive), so to keep up a fake air of technological evolution (as we've come to expect it from other devices such as computers or phones), they just tack things on that makes them look more advanced than it really is.

OMFG yes, I actually find that for many appliances, they really peaked in the 1950s and the actual utility has been on a plateau or decline since then. Maybe I am just getting old and cranky but I'm not excited about tools like the Nest thermostat or fancy Microwave because the more software the harder it is to reason about what the device is going to do, it becomes a mysterious black box with rules that you just can't quite spend the mental effort to figure out, because we all have better things to do with our time. Instead of our appliances being tools we use we become tools for babysitting the appliances, and a machine for vomiting up cash to the manufacturer.

There is also a lot of advertising out there to convince people that every chore is just _too_hard_ and you need a much larger number of appliances than are really necessary. Take a look at one of the many cooking competition shows to see how many appliances are actually useful in a kitchen.

A Linux-powered microwave oven

drag — Fri, 12 Feb 2016 16:53:11 +0000

> All it really needs to know is the weights the instant the door opens and closes.

You have to touch the machine in order to make that happening. You can't weigh something accurately as people are manipulating it.

A Linux-powered microwave oven

flussence — Fri, 12 Feb 2016 16:14:21 +0000

All it has to do is measure the absolute difference between the last two steady-state weights. That's not computationally demanding; my bathroom scales (the non-internet-connected red-LED-digits variety) can do it.

A Linux-powered microwave oven

fratti — Fri, 12 Feb 2016 15:21:36 +0000

> I find it oddly eccentric that the appliance companies have seemed bent for the past several decades on adding all these fancy bells & whistles to microwave ovens to fine-tune the heating parameters.

I have this creeping suspicion that's it's an attempt to differentiate themselves from the competition without actually having to innovate. A lot of home appliances have come to a state where it would take some serious engineering to make a substantial improvement over previous models (which is expensive), so to keep up a fake air of technological evolution (as we've come to expect it from other devices such as computers or phones), they just tack things on that makes them look more advanced than it really is.

One anecdote I have of kitchen appliances that have essentially reached an innovation plateau is when my family's old hand mixer broke. We've had it for probably over a decade, maybe even more. When my mother came back from the store, she did so with the exact same model. Same white plastic mould that would slowly become yellow over the years with a teal push button on the top to release the attachments and one switch that had several positions to adjust speed, powered with a somewhat flimsy two-wire power cord. Not only did they still produce and sell it, the salesman even recommended it to her, because essentially there have been no improvements over the years. Yes, maybe internally the power supply or the motor were using newer parts, but it's still just an electric motor that you can plug into a wall outlet to spin mixing or puréeing attachments of various shapes.

A Linux-powered microwave oven

fratti — Fri, 12 Feb 2016 14:59:31 +0000

Thinking from an accessibility angle, that actually makes a lot of sense. Thanks, didn't think of this.

A Linux-powered microwave oven

robbe — Fri, 12 Feb 2016 14:55:00 +0000

I also cannot understand why one would choose a „normal“ microwave oven. The one I use everyday is only one step up from your grandmother’s variety: in addition to the (mechanical) timer it sports a „power level“ selector (choosing the PWM duty cycle). And I actually inherited it from my gran.

David’s additions, though, seem to provide more value than the usual ones (a clock that’s always wrong, silly menus, …). I especially like the infrared sensor. I am less excited about the lack of a turntable. But maybe this spinner part can replace it reliably?

A Linux-powered microwave oven

johill — Fri, 12 Feb 2016 11:20:28 +0000

wouldn't a (really good) varying reflector (or so - "wave mixer") solve that?

A Linux-powered microwave oven

pr1268 — Fri, 12 Feb 2016 00:14:56 +0000

I'm sure everybody in here has one or more home appliances where 90% of the buttons go unused because it's just not worth the hassle to look up what they do, mostly because the basic functionality already does the job well enough.

A resounding "Amen!" to that.

A microwave oven is merely a Faraday cage with a magnetron, a lamp, a swing-out latching front door, and an on/off switch for the magnetron (since it only has two working states: full-power and off).

I find it oddly eccentric that the appliance companies have seemed bent for the past several decades on adding all these fancy bells & whistles to microwave ovens to fine-tune the heating parameters. Note that I said "heating" and not "cooking"—you really can't cook with a microwave oven. And, considering how dielectric heating works, you can't effectively heat anything which does not contain water.

I sincerely do not mean to impugn Mr. Tulloh's hard work nor Neil's excellent article. In fact, I'm quite impressed with some of the ingenuity shown by this project. But, there's something to be said about the KISS method—especially when you're working with a device that has only two discrete states of operation.

</minor rant>

P.S. I have fond memories of using my grandmother's microwave oven (vintage early 1980's). It had only two controls: (1) an egg timer-style power knob, and (2) a large mechanical latch button to open the door. Worked great for years.

A Linux-powered microwave oven

dlang — Thu, 11 Feb 2016 23:33:08 +0000

> Andrew Tridgell in the audience wondered if tempering chocolate — a process that requires very precise temperature control — would be possible.

unlikely, not because the controls aren't precise enough, but rather because the heat generated is so uneven. This is why most microwaves have turntables in them, to try and move the food around through the hot/cold spots.

Microwaves operate at ~2.4GHz and the wavelength at that frequency is ~5 inches, so your hot spots are going to end up far enough apart that they won't be solved by natural convection through the item being heated.

A Linux-powered microwave oven

neilbrown — Thu, 11 Feb 2016 21:46:35 +0000

> I've never particularly felt the need to talk to my microwave

Neither have I. But my father-in-law had "the shakes" - his hands only did approximately what he asked them to. Buttons are often unforgiving if you hit the wrong one or press too many times. His voice worked perfectly well though.
And the other commenter who carries a bowl of soup with two hands... imagine the solenoid which usually locks the door being given a reverse current when you say "Open Sesame" so that the door swings gently open.

A Linux-powered microwave oven

neilbrown — Thu, 11 Feb 2016 21:36:13 +0000

> stirring fan

Ahhh. That's what they are called. That explained the "stirrer" in the slide at
https://www.youtube.com/watch?v=R3DADx5z-XY&t=183
which had me mystified.
Thanks.

A Linux-powered microwave oven

drag — Thu, 11 Feb 2016 21:33:25 +0000

You'd have to float the internals then. You couldn't have the parts you weigh have a firm connection to the housing.

Then to keep it from wiggling around you'd have to have some extruded aluminum railings or something like that as well. Then you'll have to test it to make sure that as the thing ages the vibrations from the transformer or microwave radio to do do anything odd to create a noise in the system and various other things. And it all has to be robust enough to survive shipping and being handled by the customer.

All in all adding platform with a couple sensors under it in the oven is easier.

A Linux-powered microwave oven

iabervon — Thu, 11 Feb 2016 20:34:18 +0000

I bring my bowl of soup over to the microwave, but to open the door, I need a free hand, and I don't want to spill the soup, so I put the bowl down on the microwave, open the door, put the bowl inside the microwave, close the door, and the microwave tells me it doesn't weigh anything.

I think the points where the internals are mounted to the case might be the best place to measure, although any of these clever measurement locations depends on having a connection that's both secure and measures pressure.

A Linux-powered microwave oven

jnareb — Thu, 11 Feb 2016 11:27:24 +0000

> Placing a scale reliably under the rotating plate typical of many microwave ovens would be a mechanical challenge that Tulloh did not think worth confronting. Instead his design is based on the “flat-plate” or “flat-bed” style of oven — placing a sensor at each of the four corners is mechanically straightforward and gives good results.

The rotating plate in microwave oven is here to ensure even heating. If it is not used, then (probably more expensive) metal wave guide stirring fan is needed.

A Linux-powered microwave oven

fratti — Thu, 11 Feb 2016 10:46:25 +0000

As much as I hate the trend of putting overly complicated digital logic into home appliances, the way this project approaches the idea is actually to my tastes. Instead of offering pre-programmed functions for certain use-case scenarios that nobody will make use of in the real world, it equips the device with the sensors and logic to actually make it easier to understand for mere human beings.

I'm sure everybody in here has one or more home appliances where 90% of the buttons go unused because it's just not worth the hassle to look up what they do, mostly because the basic functionality already does the job well enough. Here, the sensors also give you a feeling of confidence that the functions actually work as advertised, since it's not just a pre-programmed set of parameters, and they also provide protection against both human and machine error when using basic microwave functionality.

IoT vendors, take note. Features should not be tacked on, but actually make sense in the context of the whole product.

What irks me though is that it seems like there is no effort to arrive at a coherent well-rounded product, especially considering proposed "features" such as voice input. I've never particularly felt the need to talk to my microwave as pressing a button is usually faster and less involved. I'm also not too sure about the touch screen; I feel like all common interactions one might have with a microwave interface could be achieved at a lower cost with a better feel by combining a display with some context-dependant physical buttons and turn knobs below or on the side.

A Linux-powered microwave oven

felixfix — Thu, 11 Feb 2016 07:31:15 +0000

That might not be much of a problem. All it really needs to know is the weights the instant the door opens and closes. Weight changes with the door closed can't have anything to do with the food inside. There's probably more error coming from container weight.

A Linux-powered microwave oven

ernest — Thu, 11 Feb 2016 06:59:42 +0000

Except that people put things on top of the oven too. Even temporarily while they wait for the cooking to finish.

A Linux-powered microwave oven

roskegg — Thu, 11 Feb 2016 05:41:22 +0000

When you're building a microwave oven enclosure from scratch, that isn't an issue. The scale is built into the box.