1 2 3 4 5 231 Replies Latest reply on Sep 25, 2012 5:22 AM by Roger Wolff Go to original post
      • 30. Re: RG1 1.8v regulator
        PeteL

        Hi Troy & all

         

        Since this thread and Coder27's thread are actually all about the same issue, can we recombine or something.  Alternatively I'll limit my replies to the one or other so at least we can keep the flow going.

         

        People coming to the forum will recognise a 'hot' SMSC if they have one, so that might be the best place?

         

        Comments / Ideas?

         

        Playing back video ramps the current requirement of the BCM considerably, again with RG1 o/c can you measure the surface temp of the SMSC?

         

         

        Cheers

         

        Pete

        • 31. Re: RG1 1.8v regulator
          morgaine

          Nice to see you here again, Pete.

           

          My finger is quite toasty now from all the finger tests on my very hot LAN9512.  Looking forward to your input on this!

           

          Morgaine.

          • 32. Re: RG1 1.8v regulator

            I came across a document "Standards for School Premises" at

              http://www.plymouth.gov.uk/standards_for_school_premises_dfes-3.pdf

            that says:

             

               Hot Surfaces   

               83. Some pupils are more at risk than others from hot surfaces. In special

                schools, nursery schools and in teaching accommodation used by nursery

                classes, the surfaces of radiators and exposed pipes located where they

                might be touched by a pupil must not become hotter than 43 degrees C.

             

            This probably isn't directly relevant to electronic devices, but it might suggest

            that uncovered electronics with blisteringly hot chips may be considered a

            safety hazard in schools.

             

            In California, hot surfaces of 140 degrees F (60 degrees C) are considered

            a safety hazard in the workplace.

            http://www.dir.ca.gov/oshsb/hot_surfaces_isor.pdf

            • 33. Re: RG1 1.8v regulator
              morgaine

              If you recall our "Finger Contact Survival Time" (:-) testing over in this thread , although initial contact temperature on my Pi was such that pure instinctive body reaction tore the finger away in a fraction of a second to avoid harm, subsequent fingers survived contact for progressively longer periods, indicating that the LAN9512 has low heat capacity and/or high thermal resistivity in its surface material.

               

              Those tests tell me that it's not really a danger in the safety sense.  The temperature is below ignition point for all common materials, and there's not enough of a heat reservoir there to maintain its temperature if coupled to anything that is thermally conducting.  The main danger to humans is probably from the instinctive reaction:  a schoolkid's sudden violent withdrawal of their hand could knock out another kid's eye or break something.

               

              The other thing that those tests tell me is that the main problem doesn't seem to be too much heat being generated but not enough heat being conducted away through the solder connections, because the surface of the device isn't able to conduct nor radiate much heat away at all.

               

              For reference, link to post with thermal image showing the 65.1C peak temperature on LAN9512 .

               

              PS. Because of the low heat capacity and/or high thermal resistivity of the surface material, a thermocouple attached to the surface is likely to indicate a lower temperature than a thermistor.  The thermocouple is entirely metallic and hence very likely to be a good conductor of heat away from the device.  A non-contact measurement like Remy's is best here.

               

              Morgaine.

              • 34. Re: RG1 1.8v regulator

                Yes, I recall the "Finger Contact Survival Time" discussion,

                but I'm not sure how relevant it is. As you say, if you pull away

                the first finger in a fraction of a second, you can use subsequent

                fingers for longer.  But the safety concern is whether the first

                finger will get burned if not pulled away in a fraction of a second,

                because younger children, older adults, and the disabled are

                assumed to have slower reflexes.

                • 35. Re: RG1 1.8v regulator

                  Pete,

                   

                  Here's some additional data.

                   

                  To hopefully make these reasonably repeatable, here's some detail of the setup I've been using

                   

                  2012-07-15-wheezy-raspbian.img no firmware/kernel upgrades done.

                  overscan disabled

                  1600x1200 Dell 2007FP monitor

                  all 'idle' readings taken while at a text based login prompt, X has not been started

                  'playing video' readings taken after running startx and then omxplayer from a terminal to play a 720p h264 mkv file

                  temperature readings taken with a MCP9803 i2c temperature sensor on top of the lan9512

                  5v applied via the GPIO header with 16/0.2 cable and I'm arranging that TP1-TP2 reads 5.00v

                   

                  Ambient, today:

                  outside 20C

                  inside 26C

                  50.3% RH

                  1005 hPa

                   

                  at each step I'm giving the board 15mins to reach equlibrium

                  The blue column at the end is the unloaded voltage reading from RG1 while it's off the board.

                   


                  RG1 on boardRG1 Removed
                  SerialIC3 idleIC3 playing videoIC3 1.8vIC3 idleIC3 temp playing videoRG1 Voltage
                  FN12071161850C / 1807mV54C / 1805mV1807mV50C / 1806mV54C / 1804mV1806mV
                  FN12072066451C / 1822mV53.5C / 1819mV1822mV50C / 1822mV53.5C / 1819mV1803mV
                  FN12072617851C / 1831mV53.5C / 1828mV1831mV50C / 1832mV53.5C / 1828mV1795mV
                  SC888 20120317135450C / 1807mV52C / 1806



                   

                  Sorry, but I won't be pulling RG1 off that last board, hope you understand why

                   

                  I have a couple of boards from FN120720xxx FN120722xxx, but as my results are mostly similar I've just picked either end of the range I have along with a couple in the middle.

                  • 36. Re: RG1 1.8v regulator
                    PeteL

                    Selsinork

                     

                    Thank you so much for this great piece of work, really helpful.  Cannot wait to try some FN1204xxxx,FN1205xxxxx boards with the same configuration.

                     

                    I'll let you know how I get on.

                     

                    (I wonder if this post will dissolve into the Ether as soon as I post? )

                     

                    Cheers

                     

                    Pete

                    • 37. Re: RG1 1.8v regulator
                      morgaine

                      PeteL wrote:

                       

                      (I wonder if this post will dissolve into the Ether as soon as I post? )

                       

                      You're in luck Pete!  The SHA-512 of the characters in the subject line multiplied by the current distance to Jupiter in furlongs added to the day of the week is not prime!

                       

                      Or maybe Loki was so stunned at selsinork's awesome chart that he forgot his usual duties.

                       

                      Morgaine.

                      • 38. Re: RG1 1.8v regulator
                        morgaine

                        Pete, if your examination of Pi design around the LAN9512 leads to board changes in that area, you might wish to consider the problem of self-powered USB hubs attempting to power the Pi upstream through their A-B lead, which typically fails and sends the Pi into a rapid continuous reboot cycle and a consequent rapid power cycling of attached HDMI equipment.

                         

                        I reported it in a thread here -- http://www.element14.com/community/thread/19316?tstart=0

                         

                        Unfortunately this affects an official Farnell "Pi Accessory" hub, and I'm sure it's not the only one.

                         

                        Morgaine.

                        • 39. Re: RG1 1.8v regulator
                          jamodio

                          Catching up after some vacations.

                           

                          NO IT IS NOT OK to use the VDD18CORE pins as an output supply, they pins are there only to hookup the

                          decoupling caps for the internal regulator.

                           

                          Glad you guys had a chance to test the theory, if the Gerbers match the schematics, and the actual PCB match the Gerbers, that's a hardware error on the Rpi, I don't think that there is much more to say.

                           

                          -J

                          • 40. Re: RG1 1.8v regulator
                            Tooms

                            Hi all and hallo to the forum from Copenhagen Denmark

                             

                             

                            I have done some testing to try out what your guys saying.

                             

                            1. using switchmode power
                            2. the LAN9512 is having an buildin LDO there is haveing higher volt level then the LDO RG1 has and because of this then the LAN9512 LDO is powering the other items there is using the 1V8 and the LDO RG1 is not doing any work.

                             

                            So i was thinking why not just try add some ebay LM2596 switchmode boards in paralle with the two LDO RG2 3V3 and RG1 1V8 to see if i can get it to use less power and get the LAN9512 to run cooler, so i just add some wires to the RG1 and RG2 and then add the LM2596 with the volt level just an small bit higher then the RG1/LAN9512 and RG2 was showing and by this let the LM2596 do the work..

                             

                            To the raspberry i connected the buildin network card to the switch and then another usb wireless netcard connected to my wireless network with WPA2 encryption and then an usb webcam to have some things to use power via the network and usb ports.

                            I then ask the raspberry to take 10000 single images from the webcam with ffmpeg and at the same time i copy some files over the wireless network, this process was running for about 30-45 minutes each time to get the temperature to get stabile

                             

                            Background rum temperature is 25.5C (measured with Fluke 54II)

                             

                            The Volt level is measured with an Fluke 8846A

                             

                            The Amp reading is the reading from the powersuppy (HP 6632B)


                            This is photo of the setup (and alot other things sorry for the mess)

                             

                             

                             

                             

                             

                            Here is test 1

                            Work: Idle mode
                            Power: Power from buildin RG1 and RG2 LDO
                            Amp reading = 541.10 mA
                            RG2 5V0 pin = 4.96150v
                            RG1 3V3 pin = 3.32753v
                            RG1 1V8 pin = 1.81029v
                            Raspi watt =  (4.96150v * 0.54110A) = 2.68466W
                            temperature - sorry have not taking any images of this

                             

                             

                             

                             

                             

                            Here is test 2

                            Work: Idle mode
                            Power: Power from the onboard LDO and two paralle switchmode LM2596 there is set to 1V8 and 3V3
                            Amp reading = 443.20 mA
                            RG2 5V0 pin = 4.98338v
                            RG1 3V3 pin = 3.35214v
                            RG1 1V8 pin = 1.84575v
                            Raspi watt =  (4.98338v * 0.44320) = 2.20863W

                            Here is an IR images of the PI at this test and the temperature is 49.5C on the LAN9512

                             

                             

                             

                             

                             

                            Here is test 3

                            Work: capturing images from webcam and copy data via the wireless network
                            Power: Power from buildin RG1 and RG2 LDO
                            Amp reading = 671.51 mA
                            RG2 5V0 pin = 4.93466v
                            RG1 3V3 pin = 3.32762v
                            RG1 1V8 pin = 1.81068v
                            Raspi watt = (4.93466V * 0.67151A) =  3.31367W

                            Here is an IR images of the PI at this test and the temperature is 59.2C on the LAN9512

                             

                             

                             

                             

                             

                            Here is test 4

                            Work: capturing images from webcam and copy data via the wireless network
                            Power: Power from the onboard LDO and two paralle switchmode LM2596 there is set to 1V8 and 3V3
                            Amp reading = 553.19 mA
                            RG2 5V0 pin = 4.96022v
                            RG1 3V3 pin = 3.34853v
                            RG1 1V8 pin = 1.84341v
                            Raspi watt = (4.96022v * 0.55319A) =  2.74394W

                            Here is an IR images of the PI at this test and the temperature is 51.3C on the LAN9512

                             

                             

                             

                             

                            So it seems by add two switchmode power suppy modules for the 3.3V and 1.8V instedt of the LDO then it is using 0.5 watt less power and is running around 8C cooler on the LAN9512.

                            I guess it will be even better if removing the LDO's from the board and only use the switchmode modules like the ebay LM2596 modules i got from china.

                             

                             

                            as a side note, i have also bypassed the USB fuses with direct 5v at the fuse on the usb side and i need this to be powering the usb netcard and webcam.

                             

                             

                             

                            Tooms

                            • 41. Re: RG1 1.8v regulator
                              electron2

                              As shown in Troy Mackay's post on Jul 28 it seems to me that we could mod our PI's to work more as the chips were designed.

                               

                              I think that this could make the PI more stable, from the looks of it.

                               

                              I am not a designer Just an old tech, but I think we need to find a way to FIX what we now know is an error in the board.

                               

                              So could someone do some practical testing to see if there is something that can be done to easly fix the current board, rather than wait for RPI foundation to fix it by waiting for a board redesign?

                              • 42. Re: RG1 1.8v regulator
                                Tooms

                                i will love to try out the hack Troy mackay has done also and then test again with that fix on the board, but i have looked into this and i most say it is very well done by Troy as i think it is to small for me todo and i done have an microscope as need for this.

                                 

                                so yes if some one can findout where to make an cut to split the LAN9512 1v8 from the lod 1v8 then i will try this also.

                                 

                                 

                                Tooms

                                • 43. Re: RG1 1.8v regulator

                                  So could someone do some practical testing to see if there is something that can be done to easly fix the current board, rather than wait for RPI foundation to fix it by waiting for a board redesign?

                                  I think we'd all like an easy fix, but with the information we have available today what Troy did is likely the best we can do. Cutting three tracks and some fiddly at best soldering on of some wire links isn't for everyone though.

                                   

                                  Beyond that we need to wait to see what Pete comes up with.  If the full gerbers were available someone would have a look and see if there was an easier way to seperate the lan9512's 1.8v from the rest of the board, but even then from what the schematics suggest there's probably a 1.8v plane on layer 5 which could make it essentially impossible...  If we're very lucky there might be a single via in a favourable place that could be carefully drilled out, but that's just about as bad as Troys wire links.

                                   

                                  Tooms idea of a marginally higher 1.8v feed from an external switching regulator may be the simplest after-market mod to accomplish even if it's not ideal. There seems to be a fair bit of interest all round in replacing the linear regulators, several designs have surfaced already.

                                  • 44. Re: RG1 1.8v regulator
                                    jamodio

                                    It would help to have a nice set of Gerber files with the current pcb layout to take a look a the traces and vias to chose what is the best course of action

                                    before cutting stuff.

                                     

                                    One option could be to just lift the two VDD18CORE pins, put togeher a small board that can be placed on top where the logo is with the 3.3 and 1.8

                                    swtiched regulators, there are some very efficient and small ones like the LMZ10501 that can handle up to 1A and includes the FET and inductor

                                    on the chip, add the decoupling caps for VDD18CORE on this board and run a wire to those pins. With some work you could manage to have

                                    through hole pads to match the pads for the existing regulators.

                                     

                                    I think there are two or three tiny ceramic caps that will get hidden under the add-on board. It may work ...

                                     

                                    My .02

                                    -J

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