Atmega 2560 Fuse Bits Changed during normal use.

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#1
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I've had two customers send non-working instruments (out of about 80 total). These came back with the low fuse bits cleared!  

Simple reprogramming fix but how does this happen? 

This only has an on off button and a serial connection.

 

Thanks,

G.

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As a running AVR cannot change it's own fuses one has to suspect something like external electrical noise - were these things running in a "harsh" environment ?

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Not sure but it did past CE testing.  At first I thought maybe a cosmic ray, but when it happened a second time I wondered.  I'll see what I can find out the environment.

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My production apps have well into six figures of units in the field, and I've never seen fuse bits "changed".  [nor flash contents either, but that would be for another day]

 

So, I'd suggest the basic suspicions.  clawson said the first, noisy environment.  Now, does CE testing really focus on that, or does it focus more on not putting stuff into the environment?  From experience, AVRs subjected to noise and stresses beyond Absolute Maximum Ratings may appear to be happy, but it is really the anti-depressant drugs masking the symptoms.  Really weird stuff can happen.  I haven't had fuses change; most often symptom is lost interrupts and/or program counter "jumping" and skipping some code.  So get good noise analysis hooked up.  Tell more about the app -- a common example is unsnubbed motor starter and similar relay-type devices.

 

The other basic suspicion is BOD.  With no BOD facilities, strange things can happen with the AVR during loss of power.

 

Two of eighty is good news and bad news.  Bad news is it is real scary.  Good news is that is enough evidence that if you get a bank of those cycling under real test conditions, it will probably happen again.

 

While you are at that, be sure to start logging the date code and the stuff on the back of the failed chips.  Compare that to never-fail units.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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During CE they zapped it in many places and many times.

 

I do have the brown out voltage set 4.3V and have a MIC803 uC monitor on the board.  12V external power supply coming in.  Using a Linear micro module buck converter (LTM4623) to supply 5V.  Have a few 12V fans drawing a couple of hundred milli watts.  The uC controls a few other buck converters (LTM4623 or LTM4622A) that power some thermoelectric devices all 1-2Amps 0-5V or <1A 0-12V, a small diaphram pump <200MA) number.  Other than that it is pretty standard: 12c pressor sensors, SPI FRAM, RTC, and FLASH, thermistors. Parallel port display screen.

 

I don't know if the two units that failed even came from the same place.  Embarassed to admit that I not sure if our records are good enough to determine if they were.  But I'll see what I can find out about this one.

 

thanks

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What CE testing was done and what standards were they tested against?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Since I don't have any commercial units out in the wild, I'll ask the neophyte question:

 

Is CE testing to prevent your box from electrocuting the end user, and testing against radiated emmissions, or is it testing the susceptibility of your circuit to EMI inbound towards your circuit?

 

I don't think the two are the same.

 

I think lightning strikes, either radiated, or surges through the power lines, can also wreck havoc with some circuits.

 

JC

Last Edited: Thu. May 6, 2021 - 08:39 PM
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Not sure in general but for us it was both.  We needed to do CE for selling in Europe and I think they have a little different requirements from the US.  I need to talk to others to locate the document that says what was tested.

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There are a variety of CT tests, and, to some degree, depending on the expected end-use, the device maker chooses the set of tests. When I was doing this 15 years ago, the avaiable tests included:

 

1. Radiated emissions (what the device radiates as an RF signal)

2. Conducted emission (what the device puts onto the power lines)

3. Radiated susceptibility (whether your device continues operating in the presence of strong RF fields)

4. Conducted susceptibility (whether your device continues operating with large amplitude AC signals on the power line)

5. ESD (electrostatic discharge) susceptibility 

6. Surges (continue operating or recover properly in the presence of power line spikes)

7. Dips and sags (continue operating or recover in the presence of various low powerline situations)

 

There are some new ones that I don't know about. FCC requires testing for items 1 & 2, only, but the testing can be structured so that both CE and FCC are adequately covered in a single test. Some of these obviously do not apply to battery powered devices (e.g. conducted emissions and susceptibility though one has to be careful if battery charging is involved).

 

Short answer: a few of these are required, especially in the U.S. Some are optional. Simply saying "passed CE tests" does not say all that much.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Thu. May 6, 2021 - 08:55 PM
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ka7ehk wrote:

There are a variety of CT tests, and, to some degree, depending on the expected end-use, the device maker chooses the set of tests.

 

Good answer. Plus, for anything electronic that consumes power including battery, you need a safety test. In summary...

 

1) Safety - "thou shalt not kill or expose to danger"

2) Emissions - "thou shalt not give off anything nasty"

3) Immunity -"thou shalt continue to work normally even if a neighbouring device does not follow rule 2"

 

Whilst the first two have hard and fast prescribed limits, rule 3 is open to a lot of interpretation. What exactly is normal operation?

 

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Should have written "... variety of CE tests ..." Guess there is no CE certification for "User Typing Accuracy" because this microscopic Apple wireless keyboard and its ancient user would both fail!

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Fri. May 7, 2021 - 06:11 AM
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ka7ehk wrote:

Should have written "... variety of CE tests ..." Guess there is no CE certification for "User Typing Accuracy" because this microscopic Apple wireless keyboard and its ancient user would both fail!

 

And maybe add UKCA to you list of acronyms! cool

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."