Electronics inside the microwave.

[Ian Stirling]

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

 

[Rene Tschaggelar]

Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

Yes, that cooking temperature is dependent on pressure or height.
At 3000m above sealevel, water cooks some degrees lower than
those 99DegC.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[Ian Stirling]

Rene Tschaggelar <none@none.net> wrote:

Ian Stirling wrote:
I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

Yes, that cooking temperature is dependent on pressure or height.
At 3000m above sealevel, water cooks some degrees lower than
those 99DegC.

True;.
I'm kind of making the assumption that my home will not suddenly lift
several thousand meters in the air.

However, if this happened, I think the microwave malfunctioning
would not be at the top of my list of priorities

 

[Peter Bennett]

On 14 Oct 2004 18:52:54 GMT, Ian Stirling <root@mauve.demon.co.uk>
wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

Yes - a microwave oven heats the food, not the air in the oven, so you
would need to put the temperature sensor in the food.

Also, placing electrical conductors in a microwave oven is generally a
Bad Idea - the microwave energy will induce voltages in the
conductors, with unpredictable results on any circuits connected to
them.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[Scott Stephens]

Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

I don't think microwave "ovens" are designed to withstand constantly
high temperatures. The box would probably not insulate its contents and
dissipate heat (away from electronics) properly.

BTW the magnetrons are 2.5 GHz, IIRC.

Perhaps an infrared sensor aimed at the food? That takes a couple
chopped IR sensors operating at different wavelengths, say 10uM & 1.5
uM, piezoceramic and PbS, for instance. Probably a pain.

Don't some ovens have a temperature probe (thermistor/thermocouple/LM35,
et.) that sticks in the food to regulate power?

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

Those who sow excuses shall reap excuses

**********************************

 

[Mac]

On Thu, 14 Oct 2004 18:52:54 +0000, Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

I think it will be hard to get any kind of signal out of a microwave oven
via wires. The wires will experience very high voltages and self-destruct
spectacularly.

Likewise, any metallic item in the microwave is apt to do the same thing
unless it is much smaller than the microwave wavelength. The fundamental
is around 2.5 GHz, I think. I don't know how far down the harmonics are,
but they might still be pretty strong.

However, I think you could embed some kind of temperature sensor in the
food (even a metallic or semiconductor one), because the food would then
protect the sensor from the microwave exposure. But how to get the signal
out? IR? Ultrasound?

Practically speaking, I think you can just give up now and save yourself a
lot of trouble. ;-)

--Mac

 

[Ian Stirling]

Scott Stephens <scottxs@comcast.net> wrote:

Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

I don't think microwave "ovens" are designed to withstand constantly
high temperatures. The box would probably not insulate its contents and
dissipate heat (away from electronics) properly.

BTW the magnetrons are 2.5 GHz, IIRC.

But the generaterd signal would be double this.

Perhaps an infrared sensor aimed at the food? That takes a couple
chopped IR sensors operating at different wavelengths, say 10uM & 1.5
uM, piezoceramic and PbS, for instance. Probably a pain.

Especially with steam/fat/... condensing on it.

Don't some ovens have a temperature probe (thermistor/thermocouple/LM35,
et.) that sticks in the food to regulate power?

Yes.

 

[Spajky]

On 14 Oct 2004 18:52:54 GMT, Ian Stirling <root@mauve.demon.co.uk>
wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

maybe an infrared sensor diode mounted in a hole on that MW owen´s
door (possibly on the outer side, that MW do not fry it) poited to the
food on the plate & connected to some circuity to pilot (on/off) the
magnetron thru owens electronics could do the job?
--
Regards, SPAJKY ÂŽ
& visit my site @ http://www.spajky.vze.com
"Tualatin OC-ed / BX-Slot1 / inaudible setup!"
E-mail AntiSpam: remove ##

 

[Rich Grise]

On Fri, 15 Oct 2004 07:51:42 -0700, Bill Schuh wrote:

On Thu, 14 Oct 2004 18:52:54 +0000, Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

My Amana RadarRange has a metal sheathed thermistor for use in the
food. It has a standard microphone plug that plugs into a bulkhead
connector on the microwave chamber. Not sure how they avoid the
problems you mention but they do somehow. The sheath is rarely
totally immersed in the food when in use so there is some method
besides being shielded by the food.

The horrors of "metal in the microwave" have been vastly overrated.
I inherited one of the first microwave oven cookbooks, when nobody
knew about these mysterious new cooking rays. In one picture, there's
an ice cube wrapped in aluminum foil sitting next to a cup of water. The
water boils, and the ice stays frozen. It didn't burn down the house. If
you're defrosting a pound of burger, and the corners get soft before the
inside, they recommend covering the "done" parts with foil to shield them
from the invisible rays. ;-)

My point is, just putting metal in the oven doesn't automagically cause
mayhem and destruction. The walls of the thing are metal, for goodness
sakes, how do you think they keep them from causing plasma storms?

It can make nice coronas and arcs if there are little pointy things
and stuff, but even if you happen to put in a piece that's a good antenna
at 2.4 GHZ, if you haven't got a detector of some kind, it will just
reradiate.

And a foil-wrapped potato won't even get warm.

They used to say "don't run it empty", but I'd think somebody's put
in some kind of load isolation by now, so even that's kind of a wash
these days.

Cheers!
Rich

 

[Jonathan Kirwan]

On 14 Oct 2004 18:52:54 GMT, Ian Stirling <root@mauve.demon.co.uk> wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

Well, you are expecting an interaction with the microwaves used to heat the food
to now generate your externally sensed signal. In other words, your device is
by definition going to need to be directly exposed to and interact with the
microwaves, themselves. Seems to me that this will cause your device to spark
and otherwise self-destruct over time and also read more of its own reaction
than that of the surrounding food unless you have a precise plan how to overcome
it. On the other hand, if you imagine that the food will absorb the energy then
how will your device interact with, then generate, and then propagate to the
outside the signal you want to observe?

I'd say... just try it without the detection part (which makes it very easy and
cheap, since those parts are easily obtained) and see how things proceed. If it
doesn't spark or get tanned or get much hotter than the surrounding food itself
(check quickly) then maybe the rest is worth some experimenting.

Jon

 

[ChrisGibboGibson]

Some amusing things to try in a microwave.

Small flourescent tube, they light very brightly.

Incandescent bulb, light very brightly, very briefly.

Xmas tree lights.

LEDs

Blue bottles buzz like a demented thing.

And finally, worms can travel much faster than I thought.

Gibbo

 

[Jonathan Kirwan]

On 15 Oct 2004 18:37:29 GMT, Ian Stirling <root@mauve.demon.co.uk> wrote:

I'm talking about something well, well under a wavelength.
Maybe 2cm dia externally.

Ah! I didn't recall reading that!

Jon

 

[Jonathan Kirwan]

On 15 Oct 2004 18:55:30 GMT, chrisgibbogibson@aol.com (ChrisGibboGibson) wrote:

Some amusing things to try in a microwave.

Small flourescent tube, they light very brightly.

Incandescent bulb, light very brightly, very briefly.

Xmas tree lights.

LEDs

Blue bottles buzz like a demented thing.

And finally, worms can travel much faster than I thought.

I'm just glad she can't read this stuff!

Jon

 

[ChrisGibboGibson]

Jonathan Kirwan wrote:

On 15 Oct 2004 18:55:30 GMT, chrisgibbogibson@aol.com (ChrisGibboGibson)
wrote:

Some amusing things to try in a microwave.

Small flourescent tube, they light very brightly.

Incandescent bulb, light very brightly, very briefly.

Xmas tree lights.

LEDs

Blue bottles buzz like a demented thing.

And finally, worms can travel much faster than I thought.

I'm just glad she can't read this stuff!

Jon

But think of the fun she'd have.

Gibbo

 

[Rich Grise]

On Fri, 15 Oct 2004 18:36:10 +0000, Jonathan Kirwan wrote:

On 14 Oct 2004 18:52:54 GMT, Ian Stirling <root@mauve.demon.co.uk> wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

Any fundemental problems with this?

Well, you are expecting an interaction with the microwaves used to heat the food
to now generate your externally sensed signal.

I agree. If all you're doing is monitoring the microwaves, you might
as well be monitoring "is the magnetron on". It will tell you nothing
about the temperature of the food, which is why people have been talking
about probes. I have used a pyrometer to measure the temp. of an object
in a chamber - this was bread in a vacuum cooler.

<story>
When you get the bread out of the oven, you can't slice it until it cools
some. For a bakery, this is very expensive, having bread just sit there on
a rack cooling, and not going out the door. I've seen a loaf of bread go
from about 250F to about 80F in about 30 seconds. You pump it down, the
water that was going to evaporate anyway evaporates, and sucks the heat
out of the bread as it does. The vacuum lowers the boiling point, you see.

</story>

But anyway, a pyrometer is another way to measure the food temp,
but that's only on the surface, which would be misleading anyway.

I'd go with the thermistor probe.

And about controlling - there's a microwave at my office that has a
"defrost" setting, and what it does is run for about 15 seconds,
and idle for about a minute, and run for about 15 seconds, and so
on, so you don't need any kind of fast switch, if you were thinking
of PWM control. I guess it's still PWM, just with a period of about
a minute or so.

Cheers!
Rich


Cheers!
Rich

 

[Rich Grise]

On Fri, 15 Oct 2004 18:35:36 +0000, Jonathan Kirwan wrote:

On Fri, 15 Oct 2004 18:00:40 GMT, Rich Grise <rich@example.net> wrote:

The horrors of "metal in the microwave" have been vastly overrated.
....
Where
I've seen serious damage occur is in the mica covering the magnetron waveguide
into the chamber -- which often develops burn holes and is eventually demolished
(perhaps, it's good design here creating a weak point intentionally.) But also,
the wave guide itself is melted at the corners and rim at the exit -- this is
permanent. None of this particular damage takes place when there is no metal in
what she inserts (which may still, of course, catch fire, though.)

Except for the fire, this is the kind of damage I'd expect from not having
enough moist stuff in the chamber to absorb all the RF energy, so it
reflects back into the waveguide, and into the maggie, and makes standing
waves, and you've seen the rest. I worked with maggie transmitters in the
USAF, and they usually had a load isolator to protect the maggie from
reflected power. Apparently, your oven(s) didn't. Sorry.

Whether or not some bit of bimetal can cause all this havoc is another thing, of
course. But intentionally putting reflectors/edges in the chamber volume isn't
'good'.

True. It can be done under the right circumstances, and with care, but in

general, don't just throw metal in there and expect it to cook. ;-)

CHeers!
Rich

 

[Mac]

On Fri, 15 Oct 2004 07:51:42 -0700, Bill Schuh wrote:

Mac <foo@bar.net> wrote in message news:<pan.2004.10.15.05.43.37.714210@bar.net>...
On Thu, 14 Oct 2004 18:52:54 +0000, Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

I was considering something really simple, but would like component
and general suggestions.

First, very simple idea.
Diode, shorted by a bimetallic normally open stat.
Pick up the 5.8Ghz signal generated.

Any fundemental problems with this?

I think it will be hard to get any kind of signal out of a microwave oven
via wires. The wires will experience very high voltages and self-destruct
spectacularly.

Likewise, any metallic item in the microwave is apt to do the same thing
unless it is much smaller than the microwave wavelength. The fundamental
is around 2.5 GHz, I think. I don't know how far down the harmonics are,
but they might still be pretty strong.

However, I think you could embed some kind of temperature sensor in the
food (even a metallic or semiconductor one), because the food would then
protect the sensor from the microwave exposure. But how to get the signal
out? IR? Ultrasound?

Practically speaking, I think you can just give up now and save yourself a
lot of trouble. ;-)

--Mac


My Amana RadarRange has a metal sheathed thermistor for use in the
food. It has a standard microphone plug that plugs into a bulkhead
connector on the microwave chamber. Not sure how they avoid the
problems you mention but they do somehow. The sheath is rarely
totally immersed in the food when in use so there is some method
besides being shielded by the food.

Bill

Very interesting. I'm glad you posted that. I wonder how they do that.
They might just use high dielectric strength coax or something.

I certainly don't have any kind of explanation.

--Mac

 

[Mac]

On Fri, 15 Oct 2004 18:00:40 +0000, Rich Grise wrote:

On Fri, 15 Oct 2004 07:51:42 -0700, Bill Schuh wrote:

On Thu, 14 Oct 2004 18:52:54 +0000, Ian Stirling wrote:

I was wondering about auto-simmer on my microwave (a feature it lacks).
I'd like a thing I can throw in the food, and it'll regulate the
temperature to 99C or so.

My Amana RadarRange has a metal sheathed thermistor for use in the
food. It has a standard microphone plug that plugs into a bulkhead
connector on the microwave chamber. Not sure how they avoid the
problems you mention but they do somehow. The sheath is rarely
totally immersed in the food when in use so there is some method
besides being shielded by the food.


The horrors of "metal in the microwave" have been vastly overrated.
I inherited one of the first microwave oven cookbooks, when nobody
knew about these mysterious new cooking rays. In one picture, there's
an ice cube wrapped in aluminum foil sitting next to a cup of water. The
water boils, and the ice stays frozen. It didn't burn down the house. If
you're defrosting a pound of burger, and the corners get soft before the
inside, they recommend covering the "done" parts with foil to shield them
from the invisible rays. ;-)

Interesting!

My point is, just putting metal in the oven doesn't automagically cause
mayhem and destruction.

No. Of course not. I'm not stupid. You have to turn the oven on for the
mayhem and destruction to occur. <GR&D>

The walls of the thing are metal, for goodness
sakes, how do you think they keep them from causing plasma storms?

It can make nice coronas and arcs if there are little pointy things
and stuff, but even if you happen to put in a piece that's a good antenna
at 2.4 GHZ, if you haven't got a detector of some kind, it will just
reradiate.

The best thing to put in a microwave oven is a CD (AOL CD's are handy for
this). Just go for one or two seconds. This may not be good for the oven,
but it is well worth it as a visual display.

And a foil-wrapped potato won't even get warm.

Wow. I honestly didn't know you could put anything foil wrapped in the
oven.

They used to say "don't run it empty", but I'd think somebody's put
in some kind of load isolation by now, so even that's kind of a wash
these days.

Cheers!
Rich

--Mac

 

[Mac]

On Fri, 15 Oct 2004 18:55:30 +0000, ChrisGibboGibson wrote:

Some amusing things to try in a microwave.

Small flourescent tube, they light very brightly.

Incandescent bulb, light very brightly, very briefly.

Xmas tree lights.

LEDs

Blue bottles buzz like a demented thing.

And finally, worms can travel much faster than I thought.

Gibbo

Also try compact disks. I recommend that you convince your friends to do
it rather than risk doing any slight damage to your own microwave.

One or two seconds is plenty of time to see the effect.

--Mac

 

[Mac]

On Fri, 15 Oct 2004 18:37:29 +0000, Ian Stirling wrote:

Jonathan Kirwan <jkirwan@easystreet.com> wrote:
On Fri, 15 Oct 2004 18:00:40 GMT, Rich Grise <rich@example.net> wrote:

The horrors of "metal in the microwave" have been vastly overrated.
I inherited one of the first microwave oven cookbooks, when nobody
knew about these mysterious new cooking rays. In one picture, there's
an ice cube wrapped in aluminum foil sitting next to a cup of water. The
water boils, and the ice stays frozen. It didn't burn down the house. If
you're defrosting a pound of burger, and the corners get soft before the
inside, they recommend covering the "done" parts with foil to shield them
from the invisible rays. ;-)

My point is, just putting metal in the oven doesn't automagically cause
mayhem and destruction. The walls of the thing are metal, for goodness
sakes, how do you think they keep them from causing plasma storms?

It can make nice coronas and arcs if there are little pointy things
and stuff, but even if you happen to put in a piece that's a good antenna
at 2.4 GHZ, if you haven't got a detector of some kind, it will just
reradiate.

And a foil-wrapped potato won't even get warm.

They used to say "don't run it empty", but I'd think somebody's put
in some kind of load isolation by now, so even that's kind of a wash
these days.
snip
Whether or not some bit of bimetal can cause all this havoc is another thing, of
course. But intentionally putting reflectors/edges in the chamber volume isn't
'good'.

I'm talking about something well, well under a wavelength.
Maybe 2cm dia externally.

Right. But how to get any signal out? Maybe a heavily shielded cable would
actually do it. If all else fails, apparently, you can just wrap the
cabling in aluminum foil. ;-)

--Mac