1 10 11 12 13 14 231 Replies Latest reply on Sep 25, 2012 5:22 AM by Roger Wolff Go to original post
      • 165. Re: RG1 1.8v regulator
        michaelkellett

        The designer of this battery changeover ciruit (ON Semi's fig 31) was intending to set a difference so that one regulator would do all the work if the ac power was present. The 300mV (which is obtained by assuming the nominal 6mA quiescent current flowing through the 50R resistor) gives a margin over the +/-100mV tolerance of the regulators' output voltages. It's not  a good design because the minimum quiescent current is not specified so the intended 300mV might easily be only 200mV and then a worst case pair of regulators would be sharing the load.

         

        What we do know is that the 1117 regulator can be used in pairs but since the SMSC chip makers explicitly say that their part should not the RPi circuit is still uncharted territory (and obviously just a mistake).

         

        I can't believe that they don't just put it right.

         

        Michael Kellett

        • 166. Re: RG1 1.8v regulator

          which is obtained by assuming

          See, that's the bit I don't like

           

          I can't believe that they don't just put it right.

          Hopefully they will, but for now all we have is another assumption that theres no quick and easy way to do that.  If there's a pcb respin needed then it makes sense to take some time and fix as many problems as can be identified in one go - alignment of the RJ45 would be quite high on my personal list. 

          There's likely to be some number of bare pcb's in the pipeline, so even an immediate fix could take some time to filter through to customers. We have no details of any of that, nor would I expect to ever see it, so we're left with more of those pesky assumptions

          • 167. Re: RG1 1.8v regulator
            7point62

            Hi selsinork and thanks for the reply. You're absolutely right  - no amount of assuming on our part is going to move any copper! Putting on my optimistic to the point of naïveté hat for a moment then if a board revision does come it will take some time to proto and test (properly!) - way longer than the factories' stock of the current boards (which will be pretty skinny). Raspberry Towers may be wary of moving that connector (or doing anything else that isn't absolutely imperative) given the amount of fubar already. Who knows with that lot? They certainly make assuming stuff difficult. I do detect a little more humility on the forums over there lately though. Sometimes. With certain staff. When no-one's looking. Most of the fanbois are just as obnoxious as ever though.

             

            I wonder whether the rollout (if it does happen) will be accompanied by fanfares, or whether it will be a subdued affair...

            • 168. Re: RG1 1.8v regulator
              morgaine

              selsinork wrote:

               

              If there's a pcb respin needed then it makes sense to take some time and fix as many problems as can be identified in one go - alignment of the RJ45 would be quite high on my personal list.

               

              I'm just incredulous that with so many expert hardware engineers on the various forums, the Foundation's people are so full of themselves that they refuse to do the redesign in open consultation, despite the fact that it is the community that has found all these faults.

              • 169. Re: RG1 1.8v regulator

                selsinork wrote:

                 

                If there's a pcb respin needed then it makes sense to take some time and fix as many problems as can be identified in one go - alignment of the RJ45 would be quite high on my personal list.

                 

                You would have hoped that Pete had a bunch of fixes pretty much

                ready to go by now, and that this one would just get added to the list

                without much further delay.

                 

                But I don't get the impression that Pete has been very active on RPi

                issues lately, based on him being absent from this forum (not even

                monitoring the hardware flaws and fixups thread that he started)

                and based on his recent comment that this issue was just one on

                his list of board issues to look at.  It sounds to me like the returned

                boards have just been piling up unopened in his office.

                 

                Since we aren't getting much help from Pete in understanding how

                the regulators work, is anyone able to attach a scope and measure

                any oscillations?

                 

                In post #74, Pete wrote:

                "Of the returns I have for analysis, I have still have not found a real ‘steamer’. These could be in part due to poor underfill or even a short/defect elsewhere on top of what we are asking the chip to do."

                 

                I find this interesting in regard to element14's limited warranty, which says:

                "Newark element14 warrants that the Raspberry pi will be free from defects in material or workmanship for a period of 12 months from the date of Newark element14's shipment of the Raspberry pi to you, the Customer."

                http://www.farnell.com/datasheets/1627216.pdf

                 

                Notice that "design defects" are not explicitly mentioned.  So I wonder if

                "poor underfill" would be a covered defect in workmanship, but an error in

                the schematics would be an uncovered design defect?  I presume if the

                temperatures are hot enough to be considered a safety issue, that it would

                be covered by law in most jurisdictions regardless of whether it was a

                considered to be a design issue or not.

                 

                Hopefully someone from element14 will speak up soon as to how the

                warranty applies to this design error.

                • 170. Re: RG1 1.8v regulator
                  morgaine

                  coder27 wrote:

                   

                  But I don't get the impression that Pete has been very active on RPi

                  issues lately, based on him being absent from this forum (not even

                  monitoring the hardware flaws and fixups thread that he started)

                  and based on his recent comment that this issue was just one on

                  his list of board issues to look at.  It sounds to me like the returned

                  boards have just been piling up unopened in his office.

                   

                  Since we aren't getting much help from Pete in understanding how

                  the regulators work, is anyone able to attach a scope and measure

                  any oscillations?

                   

                  It's rather likely that we've been guilty of wishful thinking regarding Pete's visits to this forum, sometimes seeing it as vindicating our view that (Foundation minus Pete) is on drugs whereas Pete as their engineer retains his professional standards and distances himself from the shenanigans of the rest of the Foundation.  Unfortunately, that's almost certainly naive in the extreme.  He knows that his toast is buttered on the RPF side, and that being seen as a small hero here does not pay the rent.  His absence and silence probably reflects reality rather than our wishful thinking:  we misjudged his desire to do the right thing for the community.

                   

                  We still don't have the old gerbers despite countless requests and no rational reason for them to be withheld, we still have no information on whether the first revision is intended to be minimal or extensive, and we still don't  have any engineering feedback about Model A operation despite the continued false advertising of "$25 computer" (it would be valuable to quantify USB faults in the absence of the LAN9512).  If Pete wanted, he could be pushing the Foundation towards being more open about these things, but this has not happened.

                   

                  While wishful thinking makes all us feel better, the facts are not encouraging:  Pete spent at most a few hours on a number of occasions gathering input from the Element 14 forum, but the information flow has been completely one-way.  I think it's time to put the rose-tinted spectacles aside.

                   

                  Morgaine.

                  • 171. Re: RG1 1.8v regulator
                    jamodio

                    Since we aren't getting much help from Pete in understanding how

                    the regulators work, is anyone able to attach a scope and measure

                    any oscillations?

                     

                    On the scope I can see just a little bit of noise less than 20mV but no oscillations, I'm hitting the ethernet port with flood packets.

                     

                    I'll put the ScopeMeter on a long term plot of 1V8.

                     

                    About my comments on analysis, etc, the issue is that we have many variables moving at the same time that induce a large deviaton on any measurements, we are not following a common test procedure or similar instruments while testing different boards to be able to produce a reasonable bell curve.

                     

                    So "it works for me" is valid report too, actually so far it has been working for me too in some aspects.

                     

                    I'm still wating to see what else Pete has on his "list" ...

                     

                    BTW I'm playing with the MK802 and the thing works out of the box with Android 4.0, no issues with the RF keyboard/touchpad, video and audio are great, yes I paid $72 for it but includes a power supply, HDMI cable, USB cable, USB adaptor, comes with a nice box and btw has a case !!, ohh and 1GB RAM, 4GB FLASH, the Cortex-A8 runs at 1GHz and the GPU at 500MHz. With all that now the R-pi feels more expensive ...

                    I've the little Gizmo attached to one of the corners of my monitor.

                    nk802-test-02.jpg

                     

                    I'll try some time later to get Ubuntu running on it

                     

                    -J

                    • 172. Re: RG1 1.8v regulator
                      morgaine

                      Cute, thanks for the pic.

                       

                      Cortex-A8 seems a good foundation on which to base a multi-machine home ARM capability.  My BeagleBone and original-version 7" Samsung Galaxy Tab both use Cortex-A8, and so does the forthcoming Olimex A13-based board (all those A10 gadgets too).  Moreover, Cortex-M3 and M4 microcontrollers use the same ARMv7 instruction architecture, so in principle one could do development on a Cortex-A8 Linux machine to target a Cortex-M3/4 series microcontroller without needing cross-compilation.

                       

                      More advanced application processors like Cortex-A9 MPcore and Cortex-A15 still retain the same basic ARMv7 instruction architecture as Cortex-A8, so there's a solid growth path into the future there too.  ARMv7 is effectively ARM's equivalent of the ubiquitous x86.

                       

                      Morgaine.

                      • 173. Re: RG1 1.8v regulator

                        Morgaine Dinova wrote:

                         

                        He knows that his toast is buttered on the RPF side, and that being seen as a small hero here does not pay the rent.

                         

                        I'm not sure the RPF is paying Pete much rent money either,

                        given that they have long claimed not to have any paid employees.

                        I think it's much more likely that he hasn't been doing much if any

                        RPi work lately because they aren't paying him much if anything. 

                         

                        When Pete first responded to this issue, he didn't say the RPF

                        asked him to respond, or that he was responding on behalf of the

                        RPF, he said Mike Powell of element14 asked him to respond.

                        Of course, the RPF may have later asked him _not_ to respond further.

                         

                        I suspect there is some checking going on regarding Pete's work

                        in designing the board, to see who is liable for fixing the problem.

                        If Pete did the work as an employee of RPF, then RPF would probably

                        be liable.  If Norcott was involved, then Norcott might be liable.

                        I notice that Pete appears to be deflecting some of the blame toward

                        Broadcom, in saying that the error was in the earlier prototype boards

                        and his work was extensively checked by the SoC experts.  I don't see

                        anybody stepping up and taking responsibility.

                        • 174. Re: RG1 1.8v regulator
                          John Beetem

                          Morgaine Dinova wrote:

                           

                          Cortex-A8 seems a good foundation on which to base a multi-machine home ARM capability.  My BeagleBone and original-version 7" Samsung Galaxy Tab both use Cortex-A8, and so does the forthcoming Olimex A13-based board (all those A10 gadgets too).  Moreover, Cortex-M3 and M4 microcontrollers use the same ARMv7 instruction architecture, so in principle one could do development on a Cortex-A8 Linux machine to target a Cortex-M3/4 series microcontroller without needing cross-compilation.

                           

                          More advanced application processors like Cortex-A9 MPcore and Cortex-A15 still retain the same basic ARMv7 instruction architecture as Cortex-A8, so there's a solid growth path into the future there too.  ARMv7 is effectively ARM's equivalent of the ubiquitous x86.

                           

                          Morgaine.

                          Cortex-A8 uses the ARMv7-A instruction set which includes both 32-bit ARM instructions plus 16/32bit Thumb/Thumb2  instructions.  Cortex-M3/4 use the ARMv7-M instruction set which only has Thumb/2 instructions.  So if you compile your programs and libraries using Thumb/2, you'll be able to run on both (unless you use integer divide -- Gotcha!)   But if you use ARM instructions, the binaries won't run on Cortex-M3/4.  Yes, it really is this complicated.  Take a look at the latest ARM ARMs (Architecture Reference Manuals).  Or better yet, download the quick reference cards.  They read like railroad time-tables with myriad footnotes.  OTOH, I am truly impressed that they're able to squeeze the intricacies of the ARM/Thumb/2 instruction sets into a few pages.

                           

                          I guess ARMv7 is equivalent to the x86 in that both evolved from a simpler architecture into a dog's breakfast.  Both are a far cry from my personal favorite, PowerPC, which was a clean, well-designed architecture long before it was implmented as an IC.  OTOH, you can't get a PowerPC board that can run GNU/Linux for under US$120.

                          • 175. Re: RG1 1.8v regulator
                            John Beetem

                            jamodio wrote:

                             

                            BTW I'm playing with the MK802 and the thing works out of the box with Android 4.0, no issues with the RF keyboard/touchpad, video and audio are great, yes I paid $72 for it but includes a power supply, HDMI cable, USB cable, USB adaptor, comes with a nice box and btw has a case !!, ohh and 1GB RAM, 4GB FLASH, the Cortex-A8 runs at 1GHz and the GPU at 500MHz. With all that now the R-pi feels more expensive ...

                             

                            I'll try some time later to get Ubuntu running on it

                            Thank you for the MK802 photo.  Cute little board, though it obviously has limited I/O.  Please let us know how Ubuntu (or any other GNU/Linux distro) goes.

                             

                            I'm also going to watch the US$49 cubieboard (http://en.wikipedia.org/wiki/Cubieboard, http://cubieboard.org/).  If cubieboard becomes real and a good community develops, it (and other A10-based boards) could be effective competitors to RasPi.  Love those 2 mm headers!

                            • 176. Re: RG1 1.8v regulator
                              John Beetem

                              jamodio wrote:

                               

                              Since we aren't getting much help from Pete in understanding how

                              the regulators work, is anyone able to attach a scope and measure

                              any oscillations?

                               

                              On the scope I can see just a little bit of noise less than 20mV but no oscillations, I'm hitting the ethernet port with flood packets.

                              I think it's really unlikely that you'd see oscillations.  My guess would be that only a handful of boards -- well fewer than 1% -- have RG1 Vref and IC3 Vref so close together that oscillation could occur.  I would guess that usually one or the other simply dominates.  OTOH, as the board heats up, dominance could shift from one regulator to the other, and you might see 1V8 oscillation at the crossover point.  But the dominance could just as easily diverge, and it could depend on NCP1117 manufacturer or lot.

                              • 177. Re: RG1 1.8v regulator
                                jamodio

                                I don't mind much about the limited I/O. On my projects list to try I've connecting it to a USB hub and to one of the IOIO boards from SparkFun that are already supported by Android and other Linux distros.

                                 

                                This is the IOIO board from SparkFun -> https://www.sparkfun.com/products/10748

                                 

                                -J

                                • 178. Re: RG1 1.8v regulator
                                  morgaine

                                  John Beetem wrote:

                                   

                                  I think it's really unlikely that you'd see oscillations

                                   

                                  Be sure to check all the way up in frequency.  The USB and ETH sections of LAN9512 are isolated with inductors specified at 100MHz, and I'm sure there's a reason for that.  HF parasitics could be very damaging even at very low amplitude.

                                  • 179. Re: RG1 1.8v regulator

                                    I'm not sure the RPF is paying Pete much rent money either,

                                     

                                    Yeah, my first thought on that was that Pete has a bill paying day job like the rest of us and is now doing this stuff in his spare time, effectively as a donation to the charity. We have no way of knowing what free time he may have or what he's willing to donate, so I'm not about to jugde him on that.

                                    When he is here I for one will offer whatever assistance I can as he does seem to be open to the engineering issues.

                                     

                                    The only other comment I'd make is that other than Eben, the other trustees don't seem to be much in evidence. There's been an occasional post by Jack Lang and a few more here by Pete, but I've seen nothing from say David Braeben or Robert Mullins other than some early interviews. So, IMHO, Petes input is welcome whenever he cares to join us.

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