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'[PIC]:: PIC18F4580 EEPROM Problems'
2012\05\21@152055 by zipwize

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I have a product based on the PIC18F4580. It works well with RS-232, RS-485 and SDI-12. But I have one application at 4000 meters of altitude where the EEPROM settings are getting corrupted at unusual times. Once the EEPROM is wiped, I loose contact with the unit. There is a 5V LDO regulator. This application has a radio with 1/10W output. The case is just aluminum. The antenna is a 3db omni that is about 5cm from the PC board. The ambient temperature did not drop below -29C this past winter. The PIC18F4580 is rated for -40. I can't believe the radio would cause this problem. Out of 40 stations, 15 were made non-functional because the address, baud rate, communication mode are all stored in EEPROM. Power is turned on every hour for 40 seconds by a data logger with RTCC. I have hundreds of these units in remote areas using RS-232 with no problems. I use the same UART for all communication modes. I use the same command parsing and EEPROM Read/Write for all modes. I just enable!
 the appropriate IC for the mode. The 40 stations all use the SDI-12 communication. I ran it in the office for weeks without issue.
I would like to hear about any theories on why this is happening.
Thank you to the PICList
Best Ragards,
Zipwiz

2012\05\21@153243 by Spehro Pefhany

picon face
At 03:20 PM 5/21/2012, you wrote:
>I have a product based on the PIC18F4580. It works well with RS-232,
>RS-485 and SDI-12. But I have one application at 4000 meters of
>altitude where the EEPROM settings are getting corrupted at unusual
>times. Once the EEPROM is wiped, I loose contact with the unit.
>There is a 5V LDO regulator. This application has a radio with 1/10W
>output. The case is just aluminum. The antenna is a 3db omni that is
>about 5cm from the PC board. The ambient temperature did not drop
>below -29C this past winter. The PIC18F4580 is rated for -40. I
>can't believe the radio would cause this problem. Out of 40
>stations, 15 were made non-functional because the address, baud
>rate, communication mode are all stored in EEPROM. Power is turned
>on every hour for 40 seconds by a data logger with RTCC. I have
>hundreds of these units in remote areas using RS-232 with no
>problems. I use the same UART for all communication modes. I use the
>same command parsing and EEPROM Read/Write for all modes. I just enable!

Have you run it in an environmental chamber at low temperatures?

>   the appropriate IC for the mode. The 40 stations all use the
> SDI-12 communication. I ran it in the office for weeks without issue.
>
>I would like to hear about any theories on why this is happening.

My thought is that you are using capacitors that do not maintain their full value at
low temperatures, and as a result your noise margin is reduced at low temperatures.

>Thank you to the PICList
>
>Best Ragards,
>
>Zipwize

2012\05\21@155002 by John Temples

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On Mon, 21 May 2012, spam_OUTzipwizeTakeThisOuTspamcomcast.net wrote:

> the EEPROM settings are getting corrupted at unusual times.

This is almost always caused by the PIC browning out.  Is the PIC
protected from browning out?

--
John W. Temples, II

2012\05\21@161033 by Bob Blick

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Battery internal resistance goes way up at low temperature. The exact
temperature depends on the type of battery. I assume you are using some
type of lithium primary battery if you are at -29C. I had to use lithium
thionyl to get reliable performance below -40C.

Bob



On Mon, May 21, 2012, at 07:20 PM, .....zipwizeKILLspamspam@spam@comcast.net wrote:
{Quote hidden}

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2012\05\21@174427 by alan.b.pearce
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{Quote hidden}

This is typical of space originated radiation, as in particles from the sun, causing erasure of the part. My quick fix would be to glue a 1mm thick piece of tantalum on top of the chip, and on the other side of the PCB, under the chip. I have seen exactly this done when using COTS parts in instruments that have been flown, as well as on EEPROMS used for onboard firmware.

You should be able to get suitable pieces of ready cut tantalum from any supplier of scientific metal sheet.


-- Scanned by iCritical.

2012\05\22@030025 by Electron

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At 23.44 2012.05.21, you wrote:
{Quote hidden}

Why not lead?

2012\05\22@071925 by alan.b.pearce

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> >You should be able to get suitable pieces of ready cut tantalum from
> >any supplier of scientific metal sheet.
>
> Why not lead?

While lead may be heavier, I believe tantalum is denser, in terms of stopping particles that occur in upper atmosphere/low earth orbit conditions.


-- Scanned by iCritical.

2012\05\22@121306 by Carey Fisher

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On Tue, May 22, 2012 at 7:19 AM, <alan.b.pearcespamKILLspamstfc.ac.uk> wrote:

> > >You should be able to get suitable pieces of ready cut tantalum from
> > >any supplier of scientific metal sheet.
> >
> > Why not lead?
>
> While lead may be heavier, I believe tantalum is denser, in terms of
> stopping particles that occur in upper atmosphere/low earth orbit
> conditions.
>
> "Where space is at a premium and radiation protection is important, lead
is often prescribed. It is recognized that lead is not the densest element
(e.g., tantalum, tungsten, and thorium are higher on the density scale),
but lead is readily available, easily fabricated and the lowest cost of
these materials." from:
www.marsmetal.com/sheet-lead/radiation-shielding
-- Carey Fisher
Chief Technical Officer
New Communications Solutions, LLC
678-999-3956
.....careyfisherKILLspamspam.....ncsradio.co

2012\05\22@200323 by zipwize

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I did some more research into my problem and I think that the Brown-out voltage protection is solution. I did not have brown-out protection on in the configuration switches. When power is removed, it takes several seconds for the voltage to drop. The PIC spends enough time in the brown out voltage range to cause the EEPROM wipe out. I was not aware that the EEPROM was susceptable to being erased or modified by low Vdd. I assumed the PIC would just shut off clean. I have not needed to use brown-out protection before. This low power application caught me by surprise. I am using Alkaline batteries. We change them twice a year. Lithium was too expensive and too difficult to ship by air. Solar panels were not allowed due to the ground cover spray that would coat the panels.
As far as radiation shielding, I once worked as a test engineer at a major a satellite company that used Molybdenum slabs on every DIP package. It was very expensive but required for space exposure. On occasion, I do remote monitoring for a Molybdenum mining company.
Thank you to the PICList for your valuable comments

2012\05\22@213234 by piclist4

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On Wed, 23 May 2012, EraseMEzipwizespam_OUTspamTakeThisOuTcomcast.net wrote:

> I was not aware that the EEPROM was susceptable to being erased or
> modified by low Vdd.

It isn't.  What happens is that the program counter can take on a
random value which causes your EEPROM write routine to be executed
unexpectedly.

--
John W. Temples, II

2012\05\22@225249 by Bob Blick

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On Wed, May 23, 2012, at 12:03 AM, zipwizespamspam_OUTcomcast.net wrote:

> protection before. This low power application caught me by surprise. I am
> using Alkaline batteries. We change them twice a year. Lithium was too
> expensive and too difficult to ship by air.
I have found that alkaline batteries basically stop working by -20C
(you'll get about 10% capacity and current), you can verify that easily
enough.

Best regards,

Bob

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2012\05\23@071712 by RussellMc

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> I have not needed to use brown-out protection before.

You HAVE needed to. You just have not realised the fact.
Brownout protection is needed as of right in every application EXCEPT
where you can utterly guarantee the need will never arise and you are
competent and qualified to make that guarantee. In the latter case it
is not essential , just almost certainly needed :-). I debated whether
to add the smiley and decided to - BUT Murphy does not do smileys and
will have no probl;em crashing you system with no BOD when he really
really wants to.

Brownout protection is not optional. If the processor has it, use it.
If the processor has not got it, don't use the processor. The ONLY
exception is where you do external brownout control. Note that
asserting a reset line or NMI line is NOT enough to recover from
brownout with certainty. The only thing that is guaranteed is a full
power off for an adquate [tm] period. I have seen IC's locked in
browned out mode with 0.2 V on their VCC line.

> This low power application caught me by surprise. I am using Alkaline
> batteries. We change them twice a year. Lithium was too expensive and too
> difficult to ship by air.

There should be no problem whatsoever in shipping primary Lithium
cells by air if this is within the US and probably within most of
Europe. In eg China you'll need specific certification at least.
People like Fedex have standard "shipping batteries by air" documents
that show what you can and can't do and how you need to prepare or
certify batteries for air transport. Note that Alkaline batteries may
also be subject to air transport restrictions.

As Alkaline capacity drops very substantially at low temperatures. You
could probably use a much lower capacity Lithium in their place.

> Solar panels were not allowed due to the ground
> cover spray that would coat the panels.

Knowing the application would help make informed comment on that.

> As far as radiation shielding, I once worked as a test engineer at a major
> a satellite company that used Molybdenum slabs on every DIP package. It was
> very expensive but required for space exposure. On occasion, I do remote
> monitoring for a Molybdenum mining company.

And, amongst other things, the man who commented on the radiation
aspects makes satellites !!! :-)



     Russell  McMaho

2012\05\23@075343 by alan.b.pearce

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> And, amongst other things, the man who commented on the radiation aspects makes
> satellites !!! :-)

And I had this woman as a colleague for a while ...

http://www2.physics.ox.ac.uk/contacts/people/aplin

Under the Research tab, note the last bullet point ...

Now look at this page ... http://en.wikipedia.org/wiki/Snowdon to get the height, and you will see that it is lower than where you are placing your equipment.

Others may be correct in that it is electrical problems getting you with brownout, but you need to be aware of the cosmic ray problem as well. It may be doing similar things as the brownout does.






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