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.
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. 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 Soekris-tech@lists.soekris.com http://lists.soekris.com/mailman/listinfo/soekris-tech
