PisRUS
Posts: 30
Joined: Sun Mar 04, 2012 1:02 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:12 pm

This is all really interesting. Hard to believe that this issue slipped through the net.

Can't wait to hear the Foundation's response - a bit of damage limitation incoming perhaps? :)

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2076
Joined: Thu Jul 11, 2013 2:37 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:16 pm

PisRUS wrote:This is all really interesting. Hard to believe that this issue slipped through the net.

Can't wait to hear the Foundation's response - a bit of damage limitation incoming perhaps? :)
In case you haven't noticed, Raspberry Pi engineering has been involved through this thread from the beginning.

It's also the weekend, which means I don't have access to lab tools I need (other than what I have lying around at home) to diagnose this further.
Rockets are loud.
https://astro-pi.org

rahlquist
Posts: 149
Joined: Tue Jan 21, 2014 1:02 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:29 pm

jdb wrote:
PisRUS wrote:This is all really interesting. Hard to believe that this issue slipped through the net.

Can't wait to hear the Foundation's response - a bit of damage limitation incoming perhaps? :)
In case you haven't noticed, Raspberry Pi engineering has been involved through this thread from the beginning.

It's also the weekend, which means I don't have access to lab tools I need (other than what I have lying around at home) to diagnose this further.
I think your response has been spot on for a weekend.

As for mitigation, I suggest you partner with Sugru and send all affected units a tiny ball of it to cover U16. It is probably what I will do.

Neil
Posts: 98
Joined: Thu Sep 29, 2011 7:10 am
Contact: Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:34 pm

All bare-die (e.g., WLCSP) packages are sensitive to light, especially at the infra-red end where silicon is virtually transparent, and indeed makes rather good IR lenses such as these ones:
http://www.edmundoptics.co.uk/optics/op ... enses/3368

It's a well-known behaviour of such packaged devices.

Neil

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23382
Joined: Sat Jul 30, 2011 7:41 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:45 pm

PisRUS wrote:This is all really interesting. Hard to believe that this issue slipped through the net.
I don't find it hard to believe. How many bits of electronics are tested by firing a flash gun at them? Did anyone here ever think this could cause a problem? I doubt it. I've never even heard of a failure case such as this. I'm sure some people have, but not that many I suspect.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

simpex
Posts: 45
Joined: Tue Feb 03, 2015 8:40 am

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:54 pm

simpex wrote:How do you explain this:
"Another ... measurement, with the board totally unplugged and powered down you get a big spike on the 3.3V line from the flash:". See post: http://www.raspberrypi.org/forums/viewt ... 02#p688202
jdb wrote:The flash lamp will also produce a very large electric field spike with principal frequencies in the RF range. This will couple into scope leads/ground loops and produce a voltage bounce even when the Pi is switched off. The only way to measure this properly is to use a differential probe on the PSU line.
You can do an easy test:
Just set the camera on flash on mode with 10 seconds trigger delay (or more if it is possible) and put it inside an opaque enclosure, a black plastic bag, a cardboard box, even a close nearby room, etc.. Then measure the voltage accross that 3.3 V line.
- If you get a signal on the scope, having the same characteristics as this one ( http://www.raspberrypi.org/forums/viewt ... 02#p688202 ) then the voltage bounce is likely due to the broad band RF signal generated by the sudden electric discharge in the (xenon) lamp.
- If you get nearly nothing then the bouncing signal, visible when the development board is not connected to any power source, is not triggered by the RF radiation.
jdb wrote:Sunlight (or at least the paltry excuse we have in the UK in wintertime) doesn't seem to affect operation of the board.
Here you can try to use a strong magnifying glass (which has the drawback of filtering the IR light) to focus the pale sunlight in the UK on the circuit suspected of creating the glitch problem. However, nothing replaces the bright sunlight. Anyway, if strong sunlight does not affect Raspberry Pi 2 it could mean that some of those infrared peaks from the Xenon Lamp ( see: http://zeiss-campus.magnet.fsu.edu/arti ... onarc.html ) are the main culprits.
IC packages are opaque to visible light, otherwise you would have seen the circuit inside through them. In conclusion visible light is likely inoffensive and not responsible for the glitch. Regarding the IR, there is no easy way to verify whether the package is transparent to this radiation or not. In the case of Raspberry Pi 2 some ICs cases can leave certain IR frequencies pass trough.
Last edited by simpex on Sun Feb 08, 2015 8:15 pm, edited 4 times in total.

Neil
Posts: 98
Joined: Thu Sep 29, 2011 7:10 am
Contact: Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 7:57 pm

jamesh wrote:
PisRUS wrote:This is all really interesting. Hard to believe that this issue slipped through the net.
I don't find it hard to believe. How many bits of electronics are tested by firing a flash gun at them? Did anyone here ever think this could cause a problem? I doubt it. I've never even heard of a failure case such as this. I'm sure some people have, but not that many I suspect.
James,

Did you ever get involved in the Majesty project? That had a CSP-packaged FM radio chip that didn't work well unless you covered it with insulating tape/finger/lab book/etc!

Neil

EJH
Posts: 2
Joined: Sun Feb 08, 2015 2:06 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 8:13 pm

Could anyone having a Pi2 please verify the solution to put a roll of blu-tac, diameter ca. 1mm, only around the sides of U16?

The sensitive part is probably the bottom of U16. Shielding only the sides of U16 should be sufficient to prevent light from going into the space between component and pcb.

The professional solution would be to use (semi-)opaque glue/lacquer. Professional lacquer should be non-conductive and slightly flexible after curing. Black would be best.

Best, EJ

simpex
Posts: 45
Joined: Tue Feb 03, 2015 8:40 am

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 8:30 pm

If you do not have blue-tac, a small ball made of bread can be used to cover either the entire IC or only its sides.

User avatar
liz
Raspberry Pi Foundation Employee & Forum Moderator
Raspberry Pi Foundation Employee & Forum Moderator
Posts: 5201
Joined: Thu Jul 28, 2011 7:22 pm
Contact: Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 9:27 pm

The bread fix is...unique. Thank you for that; it's the first bug-fix involving yeast I think we've ever seen around here.
Director of Communications, Raspberry Pi

User avatar
DougieLawson
Posts: 35809
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website Twitter

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 9:41 pm

liz wrote:The bread fix is...unique. Thank you for that; it's the first bug-fix involving yeast I think we've ever seen around here.
Isn't there a risk that it will grow a nice batch of penicillin mould? Or dry out and become a fire hazard.

BluTack (temporary) or Sugru (permanent) seems to be a better option. I still think a dab of dark nail varnish might be easiest,
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

Any DMs sent on Twitter will be answered next month.

This is a doctor free zone.

mikerr
Posts: 2774
Joined: Thu Jan 12, 2012 12:46 pm
Location: UK
Contact: Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 9:44 pm

EJH wrote:Could anyone having a Pi2 please verify the solution to put a roll of blu-tac, diameter ca. 1mm, only around the sides of U16?

The sensitive part is probably the bottom of U16. Shielding only the sides of U16 should be sufficient to prevent light from going into the space between component and pcb.
I think you may have a point, originally bluetak just on the surface didn't work, pressed down all over the chip (and sides) worked.

I can't test it anymore as I've just driven 150 miles from the Pi 2 !
Android app - Raspi Card Imager - download and image SD cards - No PC required !

gregeric
Posts: 1509
Joined: Mon Nov 28, 2011 10:08 am

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:07 pm

Is there a tinfoil HAT available? That should do it!

User avatar
STrRedWolf
Posts: 24
Joined: Fri Oct 05, 2012 1:47 am

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:09 pm

Would a 1 inch by 1 inch square of black electrical tape over U16 also work around this issue? I would assume the overlap would minimize any "signal" getting into the sides of U16.

artag
Posts: 12
Joined: Wed Nov 02, 2011 10:51 am

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:10 pm

Blu-tak around the edges was sufficient to stop the laser pointer affecting it but not the flash. You can't get much blu-tak around the edges without covering the top though. I would suspect it's not blocking a lot of light.

The flash in this case was the small popup in a Lumix DMC-FZ8 about 10cm from the board. Laser pointer was a cheap red 1mW ebay device having a badly-focussed spot of about 4mm diameter.

Bread was not tested, though I considered Marmite for improved light blocking.

tcwilsonjr
Posts: 2
Joined: Sun Feb 08, 2015 10:08 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:13 pm

It does seem the issue really may be one of light as opposed to EMP since shading one particular IC (U16) fixes the problem. A xenon discharge does have quite a different spectrum from a white LED, many semiconductors are photosensitive, and it is certainly possible that the encapsulation for one of the chips is not opaque enough.

While the RPi fabricators go looking for better epoxy a piece of metal tape on the sensitive chip should be effective. Old timers might have some of the metallized stickers used to cover EEPROM windows, otherwise you could hack something with aluminum foil and double sided tape or HVAC foil tape. To lower the chance of a little piece of metal wreaking havoc if the tape adhesive dries out someday you might want to cover it after installation with electrical tape and/or hot glue.

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2076
Joined: Thu Jul 11, 2013 2:37 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:19 pm

tcwilsonjr wrote:It does seem the issue really may be one of light as opposed to EMP since shading one particular IC (U16) fixes the problem. A xenon discharge does have quite a different spectrum from a white LED, many semiconductors are photosensitive, and it is certainly possible that the encapsulation for one of the chips is not opaque enough.

While the RPi fabricators go looking for better epoxy a piece of metal tape on the sensitive chip should be effective. Old timers might have some of the metallized stickers used to cover EEPROM windows, otherwise you could hack something with aluminum foil and double sided tape or HVAC foil tape. To lower the chance of a little piece of metal wreaking havoc if the tape adhesive dries out someday you might want to cover it after installation with electrical tape and/or hot glue.
EEPROM metal tape would be the worst thing to use here. The components around the SMPS chip are part of the power chain and shorting them out with metallic tape would render your Pi deep-fried.

In fact, it's in the "precautions for use" leaflet shipped with every Pi: do not let conductive objects or material come into contact with the board.

Also: it's amazing how many first posters on here haven't read the thread.
Rockets are loud.
https://astro-pi.org

Neil
Posts: 98
Joined: Thu Sep 29, 2011 7:10 am
Contact: Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:22 pm

jdb wrote:Also: it's amazing how many first posters on here haven't read the thread.
Welcome to the internet.

W. H. Heydt
Posts: 10768
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:30 pm

liz wrote:The bread fix is...unique. Thank you for that; it's the first bug-fix involving yeast I think we've ever seen around here.
It's all part of the effort to get Pis to live up to *your* expectations. It's the first step to equipping a Pi with a sandwich.

User avatar
aTao
Posts: 1087
Joined: Wed Dec 12, 2012 10:41 am
Location: Howlin Eigg

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 10:51 pm

liz wrote:The bread fix is...unique. Thank you for that; it's the first bug-fix involving yeast I think we've ever seen around here.
Its all about balance, finally yeast products have fixed a bug instead of being the cause (hic!)
>)))'><'(((<

tcwilsonjr
Posts: 2
Joined: Sun Feb 08, 2015 10:08 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 11:21 pm

I am a newcomer to this bulletin board. Excuse me for missing the "next page" link and thus some of the posts on this subject. Rest assured I DO read through a thread before contributing. I suggest that a friendlier response to perceived errors could result in a more productive discussion. I am a scientific instrument designer with 40+ years of electronics experience so I just might have something to contribute if I don't get snarked out of town.

In no way was I suggesting that conductive material be applied to circuit nodes. My suggestion was to apply metallic foil to the epoxy encapsulation on top of the chip that has been reported to be light sensitive. Given that some of the posts I did not see at first suggest that the sensitivity of the chip might be through the sides or even reflected onto the underside, I modify my suggestion to the following:

1) Cover the chip and surrounding area with a piece of electrical tape,
2) To this first layer, apply a smaller piece of foil, either foil tape, EEPROM sticker, or aluminum foil attached with carpet tape, spray adhesive, etc.
3) Apply a covering layer of electrical tape to encapsulate the foil if you wish,
4) Test with the xenon flash

Since the foil would provide some EM shielding too this would not be 100% definitive but it might be a helpful test as well as potentially a workaround for those who need to protect the first generation of RPi2's from this issue.

My $0.02.

User avatar
DougieLawson
Posts: 35809
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website Twitter

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 11:35 pm

Metallic foil and circuit boards are really made for each other. The risks of ending with a very dead board are too high for that to be any practical solution. Especially on a tiny component that I need a very powerful magnifying glass to locate and identify.
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

Any DMs sent on Twitter will be answered next month.

This is a doctor free zone.

User avatar
piemmm
Posts: 1
Joined: Sun Feb 08, 2015 10:52 pm
Contact: ICQ Website

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 11:37 pm

This is from guess work, but it is very likely that the discharge from the xenon flash is producing a lot of RF energy (Radio emissions) and that's getting picked up by either the RAM or CPU and corrupting/forcing some form of reset.

The RF generated by the xenon flash will be broad-band (read: visible on the whole radio spectrum - generally seen as a lot of 'inteference' that you'll see on a lot of analogue things). It's very possible that there's a wiggly-line on the CPU/RAM die that's just the right inductance to cause issues with a discharge like that

Photonic issues are probably not going to be the cause given the CPU is encased in black resin ;-) so it's possibly the spark discharge that's doing the RPi in. It'd be interesting to know if foil over the top of the ram chips and CPU will reduce the issue (alu tape will probably be ideal but be careful!!)

sylvan
Posts: 118
Joined: Sun Nov 27, 2011 8:39 pm

Re: Why is the PI2 camera-shy ?

Sun Feb 08, 2015 11:52 pm

Yes, and doing tape, foil, maybe more tape, seems to be overly complicating this problem.
  • * problem observed with xenon flash
    * problem not observed with LED flash
    * problem observed with red LASER diode
    * problem prevented by thoroughly covering U16 with blu-tack
    * minimal covering around U16 eliminates red LASER induced but not xenon flash induced problem
Conclusion: High likelihood U16 is exhibiting optical sensitivity to near infrared.

Remediation alternatives:
  • * Cover U16 with a blob of blu-tack pressed tight to the PCB around the sides of the chip.

    * If blu-tack is undesirable or not at hand, a couple of layers of black vinyl insulating tape should suffice. A single layer attenuates light significantly. If that does not suffice then add another layer until it does.

    * or covering with opaque epoxy or hot glue or RTV should also suffice, but are harder to remove in the future
And when the professionals get into the office in the morning and spend some time with their R'Pi's and test tools then they are likely to have additional information and suggestions. Until then, all is well. And frankly, this doesn't seem that big an issue. Unlikely to be seen if your R'Pi is installed in some semi-permanent manner, and remediation is easy if needed.

simpex
Posts: 45
Joined: Tue Feb 03, 2015 8:40 am

Re: Why is the PI2 camera-shy ?

Mon Feb 09, 2015 12:39 am

sylvan wrote:Conclusion: High likelihood U16 is exhibiting optical sensitivity to near infrared.
"Shining my TV remote directly at U16 had precisely zero effect. So that's a non-issue."
Source: http://www.raspberrypi.org/forums/viewt ... 58#p688458

Possible the intensity of a TV remote IR LED is not strong enough to freeze Raspberry Pi 2.

Return to “Troubleshooting”