Cold spray, where do you buy?

[Joerg]

I prefer the heat gun. Less of a stench

Well, that's CMOS.

I don't know the physics, but mosfet channel resistance and
interconnect resistance have pretty strong positive TCs, so things get
slow when they get hot. A reasonable path in and out of a Xilinx FPGA
might take 5 ns, and its TC might be in the ballpark of 5 or 10 ps/K.

That's roughly what I had on CMOS switches as well. So I servoed them
(somewhat), using another one on the same die in a DC loop. Worked quite
well but it didn't have to be perfect in my cases.

[...]

 

[Joerg]

You must be buying cheap French freeze spray. "Winter in Paris" maybe.

Now if they'd put a "Harley Davidson" aftershave scent in it, that would
be ok.

I believe you, John, but being an analog kind of guy I can't reason
why propagation delays are a radical function of temperature. Can you
explain?

Jim
Well, that's CMOS.

I don't know the physics, but mosfet channel resistance and
interconnect resistance have pretty strong positive TCs, so things get
slow when they get hot. A reasonable path in and out of a Xilinx FPGA
might take 5 ns, and its TC might be in the ballpark of 5 or 10 ps/K.

That's roughly what I had on CMOS switches as well. So I servoed them
(somewhat), using another one on the same die in a DC loop. Worked quite
well but it didn't have to be perfect in my cases.

[...]

We generally use an LM45 or an LM71 temp sensor and do the tc comps in
software, occasionally analog in hardware. Reducing prop delay tc by
maybe 5:1 is reasonable without temperature cycling production units.

I always wondered why FPGA don't have a feature to program an on-chip
temperature sensor onto one pin, or at least a diode path. uC often have
that, for example the MSP430 series.

 

[[email protected]]

Well, that's CMOS.

I don't know the physics, but mosfet channel resistance and
interconnect resistance have pretty strong positive TCs, so things get
slow when they get hot. A reasonable path in and out of a Xilinx FPGA
might take 5 ns, and its TC might be in the ballpark of 5 or 10 ps/K.
In our delay generators, we generally have to compensate. Gluing a
heat sink to the FPGA helps, and adds an air of mystery too.

One of my guys is going to engineering school part-time, and as a
project he measured the prop delay TCs of some Xilinx chips in various
situations. I'll post it if I can find it.

As I recall, TTL also slows down with temperature.

It should speed up.

ECL hardly changes at all, under 1 ps/K for a typical EclipsLite gate.

ECL also has a positive speed/temperature coefficient. We used insulators
under the Thermal Conduction Modue pistons of low power chips to equalize the
junction temperature of all chips at 85C.

 

[Kevin McMurtrie]

R134 from an auto parts dealer.

I've used one of those rechargers on a car. The valve is nothing more
than a pointed screw that stabs a hole in the canister's top. It turns
off just well enough that you can disconnect the hose without losing
fingers. The can will leak itself empty in a day or less.

I'd go for a duster can upside down. For longer term use, tech stores
catering to gamers sell all kinds of forced liquid cooling systems
involving peltier or freon heat pumps. I haven't bought one but it
looks like they use plain vinyl hoses that can be made any length.

 

[whygee]

I always wondered why FPGA don't have a feature to program an on-chip
temperature sensor onto one pin, or at least a diode path. uC often have
that, for example the MSP430 series.

The Actel Fusion family can do pretty temperature measurements,
but they are ... a bit expensive.
Maybe a ring oscillator in the FPGA fabric,
with the output frequency compared to a stable
external oscillator, can help ?

yg

 

[Spehro Pefhany]

We use Chemtronics Freez-It and some sort of duster spray. Neither
tastes or smells bad. Maybe some people are putting nasties in theirs
to discourage kids from snorting the stuff.

John

Exactly right. The Perfect Data duster I have uses the same
propellant, but doesn't have the nasty. It does leave a quite
noticable residue, so it might affect analog circuits.

http://www.3m.com/us/office/advisory/3Mdustremoverfaqs.html

Bittering Agent



What is Bittering Agent?

Bittering agent is an additive that leaves a bitter taste upon contact
with one’s mouth. 3M added a bittering agent to 3M Dust Remover to
help discourage inhalation abuse. The bittering agent itself is
generally not harmful and is used in household cleaners and shampoos
to deter intentional or accidental ingestion of these products.
However‚ people with asthma or sensitivity to odors or taste may react
to the bittering agent‚ and therefore‚ may want to avoid using 3M Dust
Remover.

Abuse by inhaling 3M Dust Remover may cause instant death or injury.



How do I get the bittering agent bad taste out of my mouth?

Dried liquid spray may leave a bitter residue‚ resulting in a bad
taste if transferred to the mouth. If you eat a piece of chocolate‚ or
drink or eat some dairy products‚ it may help the taste to go away.



How do I get the bittering agent off my fingers?

Wash affected area with soap and water. If irritation occurs‚ get
medical attention. ALWAYS hold container upright to avoid spraying
liquid. Dried liquid spray may leave a bitter residue.



How do I get the bittering agent off my keyboard?

To remove dried spray‚ wipe with a cloth dampened with a 50/50 mix of
isopropyl alcohol and water. ALWAYS hold container upright to avoid
spraying liquid. Dried liquid spray may leave a bitter residue.



Can I buy 3M Dust Remover that does not contain the bittering agent?

No. All 3M Dust Remover currently sold contains a bittering agent.



Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

It does leave a quite
noticable residue, so it might affect analog circuits.

"It" referring to the 3M product with bitterant, of course, and
noticable by humans perhaps not by circuits.

Here is info on the substance they are likely using:

http://en.wikipedia.org/wiki/Denatonium
http://www.bitrex.com/
http://www.sciencelab.com/msds.php?msdsId=9923674




Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

We tried a vortex tube and were disappointed. Not much cooling and
*very* noisy.

John

I've got a commercial one that I was just (in the last 30 seconds!)
playing with. It has a sort of muffler on the hot air output port, but
is still pretty noisy and uses a lot of air volume (but I was
expecting that). I think I might have a real application for it (first
time since finding Ranque-Hilsh (actually they only credited the
latter) in an old Amateur Scientist column decades ago)- but it's
oddball in that the air is there and comes almost for free.

http://www.visi.com/~darus/hilsch/


Best regards,
Spehro Pefhany

 

[Joerg]

The Actel Fusion family can do pretty temperature measurements,
but they are ... a bit expensive.
Maybe a ring oscillator in the FPGA fabric,
with the output frequency compared to a stable
external oscillator, can help ?

Sure, but then you have to measure frequency and, for some applications,
you've just created another EMI nightmare. A simple diode path is all
that's needed. In just about any chip design review I suggest this
because the feature is essentially free. What follows is usually a
moment of silence followed by someone saying "Oh yeah, let's do that".

 

[Joerg]

Exactly right. The Perfect Data duster I have uses the same
propellant, but doesn't have the nasty. It does leave a quite
noticable residue, so it might affect analog circuits.

http://www.3m.com/us/office/advisory/3Mdustremoverfaqs.html

Bittering Agent

That's what my client described. He said it's sort of like the "bitter
apple" stuff that you put on things that your dog wants to chew but
isn't supposed to.

 

[Joerg]

We tried a vortex tube and were disappointed. Not much cooling and
*very* noisy.

Would it be enough to disgnose thermal effects in a chip? Then we'd just
have to wait until Harborfreight has it

 

[Frank Buss]

Plus an external ADC, which may or may not be available

You can use digital inputs to convert analog values. More interesting ideas
are using LVDS inputs. This is an example from Lattice Semiconductor:

http://www.latticesemi.com/documents/WP-Creating_An_ADC_Using_FPGA_Resources.pdf

but I think this would be possible with Xilinx and Altera parts as well.

 

[Frank Buss]

I seem to remember that some (xilinx?) guy has a patent on using
the ldvs input as a comparator for an ADC

A simple digital input would do it, too. E.g. with two pins of a
microcontroller you can use a standard LED for light emitting and light
sensing:

http://www.merl.com/reports/docs/TR2003-35.pdf

Maybe this could be used with a FPGA, too, for temperature measuring with a
1N4148. But I don't know, if it needs a schmitt trigger input, which is not
available for all FPGAs (e.g. only some configuration pins on Cyclone II,
but Xilinx FPGAs have schmitt trigger inputs with 100 mV to 200 mV
hyteresis).

Of course, on page 34 of this journal:

http://www.xilinx.com/publications/archives/xcell/Xcell19.pdf

there is a simple schematic with only two resistors and two FPGA pins for a
user defined schmitt trigger

 

[John Devereux]

Sure, but then you have to measure frequency and, for some
applications, you've just created another EMI nightmare. A simple
diode path is all that's needed. In just about any chip design review
I suggest this because the feature is essentially free. What follows
is usually a moment of silence followed by someone saying "Oh yeah,
let's do that".

Forward bias one of the protection diodes?

 

[Joerg]

Forward bias one of the protection diodes?

Yup, I have used substrate diode for stuff like this but those solutions
are often met with outbursts of disgust at design reviews ;-)

 

[Joerg]

A simple digital input would do it, too. E.g. with two pins of a
microcontroller you can use a standard LED for light emitting and light
sensing:

http://www.merl.com/reports/docs/TR2003-35.pdf

That's real engineering, where competitors look at the circuit and all
they can say is "What the hell are they doing here, and how?"

[...]

 

[Frank Buss]

Yup, I have used substrate diode for stuff like this but those solutions
are often met with outbursts of disgust at design reviews ;-)

If you have the space on the board, I would use the SE95, because no
calibration is needed. I've used it with high sampling rate and digital
lowpass filter for a resolution of 0.01°C. It's fairly stable and
intersting to see the temperature falling, when slightly blowing it. I
think this could be used for something like this:

http://www.coolest-gadgets.com/20060530/electric-candles-that-you-can-blow-out/

 

[Joerg]

If you have the space on the board, I would use the SE95, because no
calibration is needed. ...

Problem is, that series is no-stock too often and that's somewhat of a
red flag for me. I2C stuff sometimes goes lalaland after a while. Mostly
I prefer a simple analog method and then either into an ADC, or
dual-slope when it has to be cheap.

... I've used it with high sampling rate and digital
lowpass filter for a resolution of 0.01°C. It's fairly stable and
intersting to see the temperature falling, when slightly blowing it. I
think this could be used for something like this:

http://www.coolest-gadgets.com/20060530/electric-candles-that-you-can-blow-out/

Oh man, electric candles with matches. That reminds me of the 2nd
generation walkman that my classmates had in school. Those had a
"talk-through" button which allowed a conversation with other kids.
Conversation, what a concept

 

[Frank Buss]

Problem is, that series is no-stock too often and that's somewhat of a
red flag for me. I2C stuff sometimes goes lalaland after a while. Mostly
I prefer a simple analog method and then either into an ADC, or
dual-slope when it has to be cheap.

I know a product, which uses it for 6 years and I think the sensor is a
standard chip, which will be in production for some more years. But the
MAX6633 looks very similar, could be replaced with no hardware changes.

How do you avoid (or implement) calibration for analog and ADC? You are
right, if you just need the information "it is hot" or "it is cold", then
you don't need complicated chips.