Hi Jeff, JSL Internet wrote: > Attila, > > Thank you for the detailed post. It is clear that you have some > understanding of best practices regarding digital PCB layout. However, > you've made a number of assumptions and generalizations. Are you > certain that there are no power and ground layers within the net5501 > multi-layer board? I would be surprised if this were true, but I'll > leave it up to Soren to clarify. The photo you posted shows four bypass > capacitors surrounding the RAM chip in very close proximity. It would > be difficult for any layout designer to get them any closer to the > chip. Sharing capacitors is just fine as long as there are separate > runs from the capacitor to each chip. The whole point of the capacitors > is to offset the inductance of the PCB power runs. It is physically > impossible to have zero-length runs from the capacitors to the chips. > The chips have small internal capacitors anyway. Your photo > demonstrates a good PCB design.
Are not really interested in commenting on Attila, especially as you seems to have received private emails off list (or the one with photo is stuck in our spam filter....). But of course the net5501 have power and ground planes, that should be obvious to any engineer, it's actually a 6 layer board. And the memory have more than enough decoupling capacitors of different sizes, just go to newegg.com and look at some pictures showing how few capacitors module manufacturers believe are needed.... > If I were having problems with a small SBC (net5501) that only > occurred when it was attached to an RF transmitter (your WLAN card), I > would be looking at the RF susceptibility of the SBC, and the isolation > of the transmission line and transmitting elements from the SBC. It's > doubtful that Soren did any RF susceptibility testing or analysis of the > computer. Most computer manufacturers do not bother with such things. > The metal boxes he sells for the SBCs should take care of most of the > problems anyway. It's entirely likely that the problems that you've > "fixed" are related to the RF susceptibility of the net5501. Small > pieces of carefully applied brass or mu-metal in selected circuit areas > would probably have accomplished the same thing that you did by adding > some capacitors. As I have stated before, afaik the net5501 do not have any design issues, Attila's problem is most likely either software related, wlan card related, or he might have a defect board (rare, but do of course happens), which I have offered to replace before. But of course not if he have ruined it with his experiments.... Best Regards, Soren Kristensen CEO & Chief Engineer Soekris Engineering, Inc. > Jeff > > On 04/06/2012 07:03 AM, Attila Kinali wrote: >> <summary> >> The power supply of the net5501 and how it is distributed to the circuitry >> is disregarding all common good design practices. Hence leading to problems >> in certain load and use conditions. These problems can be bit errors or >> complete crashes. >> </summary> > _______________________________________________ > Soekris-tech mailing list > [email protected] > http://lists.soekris.com/mailman/listinfo/soekris-tech _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
