Electronics inside the microwave.

[Mac]

On Fri, 15 Oct 2004 09:11:27 +0000, Dan Major wrote:

Mac <foo@bar.net> wrote in newsan.2004.10.15.05.43.37.714210@bar.net:

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.

This just ain't so. I work with a group researching nanomaterials and
their properties. We use a donated microwave oven as a reactor to create
silver nanowires. It's a cheap home-type oven. The rotary timer was
replaced with a solid state relay. The relay is controlled via an Omega
temperature controller. The controller uses a simple (J-type?)
stainless-clad thermocouple. The thermocouple is grounded to the oven
chamber. The turntable mechanism was removed from the bottom of the
oven, and the only problem we have had is some slight sparking where the
mesh shielding covering the hole where the turntable was removed was not
in suffecient contact with the oven chamber. Scraping paint off and
tightening the screws solved that problem. The hole in the top of the
chamber where the thermocouple is inserted is covered by a Farday cage.
As long as you insure that whatever you stick into the oven chamber is
grounded to the chamber, you will minimize problems. Otherwise, you will
need some sort of ferrite (beads, rods, etc) to reduce RF feedthrough
into your measurement circuit.

Wow. Thanks. That's very interesting.

For the OP, a thermocouple is just what he wants (but not what he
proposed), as far as I can tell.

--Mac

 

[Rich Grise]

On Sun, 17 Oct 2004 04:41:17 +0000, Mac wrote:

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

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.

Well, people have been baking potatoes wrapped in foil in an ordinary
oven since there's been foil. When uW ovens first came out, consumers
had no clue about the magic invisible rays, so had to be edjamacaited.

Cheers!
Rich

 

[Ian Stirling]

Mac <foo@bar.net> wrote:

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
snip
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.
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. ;-)

A diode causes generation of double the frequency of EM radiation
it's exposed to.
You then pick up the 5.8Ghz from that.

 

[Terry Given]

Mac wrote:

On Mon, 18 Oct 2004 14:41:23 +0000, Ian Stirling wrote:


Mac <foo@bar.net> wrote:

On Sun, 17 Oct 2004 12:24:47 +0000, Ian Stirling wrote:


Mac <foo@bar.net> wrote:

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

snip

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.

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. ;-)

A diode causes generation of double the frequency of EM radiation it's
exposed to.
You then pick up the 5.8Ghz from that.

So are you saying that you'll attach an antenna to the diode and pick up
the 5.8 outside the oven? I'm pretty sure ovens are designed to keep the
radiation IN. ;-)

Or will you carry the 5.8 out in coax?

Small antenna to pickup the 5.8 inside the cavity, with inherent blocking
of 2.4Ghz.


This is pretty far from anything I have any real practical experience
with, so I can't argue with you about it. ;-)


Anyway, I still see a couple of problems with this, both of which may have
already been mentioned in this thread.

1) All this will tell you is whether the magnetron is on, whereas what it
seems like you would want is to know the temperature of the food.

Short the diode by a bimetallic thermometer.


Again, I don't know what the properties are of a bimetallic thermometer,
so I'll just have to let this go.


2) Don't you think the magnetron puts out a fair amount of 2nd harmonic? I
mean, if it is putting out, say, 500 Watts of primary, and it has a 2nd
harmonic which is 60 dB down (I'm making this number up), that is still
half a Watt. Will your little diode pump out enough to even be detected on
top of the 2nd harmonic?

Isn't 60dB down 500uW, not 500mW?


500 Watts / 500 mW = 1000.

I am pretty sure that 20 *log (1000) = 60, so I will have to stick to my
guns on this one. ;-)

--Mac

oops. 20*log(ratio of voltages) or 10*log(ratio of powers). P = V^2/R
which is where the 10 becomes a 20..... so 10*log(500W/500uW) = 60dB

Cheers
Terry

 

[Terry Given]

Mac wrote:

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

CDs are also fun when you have a dremel. but wear safety goggles.....

Cheers
Terry

 

[Ian Stirling]

Terry Given <my_name@ieee.org> wrote:

Mac wrote:

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.

CDs are also fun when you have a dremel. but wear safety goggles.....

I'd say "just say no", unless wearing full body armour and face protection.

I tried this once, and ended up with shards of CD 2cm deep in the
plasterboard.

 

[Terry Given]

Rich Grise wrote:

On Wed, 20 Oct 2004 06:24:06 +1300, Terry Given wrote:


Ian Stirling wrote:


Terry Given <my_name@ieee.org> wrote:


Mac wrote:



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.


CDs are also fun when you have a dremel. but wear safety goggles.....


I'd say "just say no", unless wearing full body armour and face protection.

I tried this once, and ended up with shards of CD 2cm deep in the
plasterboard.


As did I. except it was thru 20mm Gib board (antipodean for plasterboard
. I figured the rest of me (and the 5 guys watching) would heal....I
was wearing a face shield (safety goggles = double glazing = instant
headache

If you Nukrowave the CD first, it self-destructs at much lower speeds.


Forgive my ignorance, but how do you blow up a CD with a Dremel?

Thanks,
Rich

Aha! odds on if you google it (i'm too lazy you'll find some nice
mpegs. If you have the dremel sander attachment (a 10mm dia or so
cylinder of rubber, about 10mm high around which a ring of sandpaper
sits), that just happens to fit nicely into the hole in the centre of a
CD (a slight interference fit). Crank it up... I suggest doing a little
bit at a time, and using your thumb to push the CD off the dremel. A
wall and a ramp allow you to make the cd spin in large loops - floor,
ramp, door, ceiling etc - the ramp shoots it backwards, but the rotation
makes it go forwards when it hits the ground. Each time it does the CD
gets damaged, and eventually flies to bits. I had a CD running at full
speed on my dremel without it bursting, but several did. Wear heavy
clothing, gloves and face protection. And ensure (not insure - grr)
no-one comes into the room while you do it. If I wasnt so lazy I'd
calculate the energy stored in the CD....oh OK, J=0.5M*(Ro^2+Ri^2)

Ro = 120mm, Ri = 15mm, t = 1.2mm so volume
V = 3.14*(120mm^2-15mm^2)*1.2mm = 53.44e-6 m^3. the CD is basically
polycarbonate, density Rho = 1.2g/cm^3 = 1200kg/m^3. sanity check:
density of aluminium = 2700kg/m^3, glass = 2600kg/m^3 so sounds OK.

M = V*Rho = 53.44e-6*1200 = 64g = 0.14lb (exactly what some of the DCD
shipping stuff I googled said)

J = 0.5*0.064*(120mm^2+15mm^2) = 468e-6 - agrees exactly with
http://hyperphysics.phy-astr.gsu.edu/hbase/ihoop.html#ihoop2

max speed = 35,000 rpm = 583.33Hz = 3665rad/s

Emax = 0.5*J*w^2 = 3kJ

fuck with this at your peril. 3kJ is enough to cause a serious injury. I
have been in close proximity to a 17kJ bang (a large inverter shat
itself while I stood beside it) and that was scary. but nothing like the
1MJ flywheel that shat itself when Stan and I were testing it
(thankfully it had a 2" Al containment vessel, securey bolted to a very
heavy plate). At a spin test for the same product, we made it fail
catastrophically by overspeeding it with a uqill shaft - died at 7.2MJ,
inside a spin pit. and melted $6,000 worth of lead bricks. man did the
building shake.

you have been warned.

cheers
Terry

 

[Mac]

On Sun, 17 Oct 2004 12:24:47 +0000, Ian Stirling wrote:

Mac <foo@bar.net> wrote:
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
snip
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.
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. ;-)

A diode causes generation of double the frequency of EM radiation it's
exposed to.
You then pick up the 5.8Ghz from that.

So are you saying that you'll attach an antenna to the diode and pick up
the 5.8 outside the oven? I'm pretty sure ovens are designed to keep the
radiation IN. ;-)

Or will you carry the 5.8 out in coax?

Anyway, I still see a couple of problems with this, both of which may have
already been mentioned in this thread.

1) All this will tell you is whether the magnetron is on, whereas what it
seems like you would want is to know the temperature of the food.

2) Don't you think the magnetron puts out a fair amount of 2nd harmonic? I
mean, if it is putting out, say, 500 Watts of primary, and it has a 2nd
harmonic which is 60 dB down (I'm making this number up), that is still
half a Watt. Will your little diode pump out enough to even be detected on
top of the 2nd harmonic?

It seems to me that the way to go is to rig up something like what Dan
Major described elsewhere in this thread.

--Mac

 

[Mac]

On Tue, 19 Oct 2004 17:39:52 +1300, Terry Given wrote:

Mac wrote:
[snip]


500 Watts / 500 mW = 1000.

I am pretty sure that 20 *log (1000) = 60, so I will have to stick to my
guns on this one. ;-)

--Mac


oops. 20*log(ratio of voltages) or 10*log(ratio of powers). P = V^2/R
which is where the 10 becomes a 20..... so 10*log(500W/500uW) = 60dB

Cheers
Terry

Sigh. Thanks for the correction. As you surmised, I was thinking of
Voltage. I am in the habit of dealing with Voltage, so I always use 20
log(x) to convert x into dB.

--Mac

 

[Rich Grise]

On Wed, 20 Oct 2004 06:24:06 +1300, Terry Given wrote:

Ian Stirling wrote:

Terry Given <my_name@ieee.org> wrote:

Mac wrote:


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.


CDs are also fun when you have a dremel. but wear safety goggles.....


I'd say "just say no", unless wearing full body armour and face protection.

I tried this once, and ended up with shards of CD 2cm deep in the
plasterboard.


As did I. except it was thru 20mm Gib board (antipodean for plasterboard
. I figured the rest of me (and the 5 guys watching) would heal....I
was wearing a face shield (safety goggles = double glazing = instant
headache

If you Nukrowave the CD first, it self-destructs at much lower speeds.

Forgive my ignorance, but how do you blow up a CD with a Dremel?

Thanks,
Rich