1 11 12 13 14 15 16 231 Replies Latest reply on Sep 25, 2012 5:22 AM by Roger Wolff Go to original post
      • 180. Re: RG1 1.8v regulator
        rrankin

        I received  my Mk802 last week. The task I would like to use it for is to

        log the performance data of my solar panels on the internet.

        The Mk802 is to replace a cat5 cable, which runs from my garage, across

        the back yard, over the dinning and living room floor to my desktop

        Fedora system which currently does my logging. My requirements are to

        use Wifi to replace the cable, run Linux, and accept an RS-485 dongle

        to interface with my inverter. These requirements are better meet by

        the Mk802, which has built in Wifi and 512MB or now 1GB ram, than the RPi.

         

        My initial setup is with the Mk802 connected to my TV with the supplied HDMI

        cable, the supplied power supply, an 8MB micro SD card, for the Fedora,

        an unpowered hub with a keyboard and mouse, and the Wifi running.

        So far I have not seen any problems with the USB devices. My Mk802

        second generation case with cooling holes runs cooler than the power pack,

        and I have not seen any Wifi problems which some people have reported.

        My Mk802 is a 512 MB version running Fedora 17 and "top" shows some swapping

        while running XFCE, two terminal emulators running, and a "yum update" in full

        progress. Although the system is still fairly responsive.

         

        Once I get the system setup, I plan to run it headless, with only the

        RS-485 USB dongle and the power supply attached. With admin access via ssh

        over the Wifi.

        • 181. Re: RG1 1.8v regulator
          jamodio

          That's a great plan Roy, glad you found a great application for it.

           

          I"m very impressed with the MK802, I didn't expect that much, not a big fan of Android as a "PC" OS but being able to run reliably run Linux on it opens the door to many applications. I'm seriously thinkin about ordering another one and take it appart as module for more complex embedded applications.

           

          Gaining access to a serial console looks very easy but I want to keep the unit I've as is like a baseline configuration and to play with the Android IOIO stuff.

           

          Good luck with your project it sounds very interesting.

           

          -J

          • 182. Re: RG1 1.8v regulator
            Tooms

            Hi

             

            I have now done the Troy Mackay fix to my test board, it was not easy to cut that small traces and then solder the wires to the board but with an microscope and time it was done and seems to work.

             

            I have also removed the RG1 and RG2, but i was not lucky with the desoldering of the RG2 as i have damage it and it is no longer working so i am using an replacement LF33CV that i have.

             

             

            So guys what testes do you like me to do and what IR images, for now i am thinking some things like this.

             

            Test 1

            Work: idle

            board: as unmodified (execpt i am using the LF33CV as RG2)

             

            Test 2

            Work: CPU is calc Pi, taking images from webcam, copy files via network

            board: as unmodified (execpt i am using the LF33CV as RG2)

             

            Test 3

            Work: Idle

            board: replace RG1 and RG2 with switchmode, disconnect the LAN9512 1V8 rail from RG1

             

            Test 4

            Work: CPU is calc Pi, taking images from webcam, copy files via network
            board: replace RG1 and RG2 with switchmode, disconnect the LAN9512 1V8 rail from RG1

             

            This is the tests i have planned for now, but i will like to hear if your guys like some other ones or changes.
            For the tests i have done see the post 40 in this thread http://www.element14.com/community/message/57800#57800

             


             

             

            Tooms

            • 183. Re: RG1 1.8v regulator
              jamodio

              Nice job.

               

              Quick tip when you need to do "airwire" mods on small pitch components, instead of using wirewrap or plastic insulated wire, you can use transformer wire that is thinner and also insulated, before soldering you can put a little bit of solder on the tip of the wire which will melt the insulating barnish.

               

              Good source of thin transformer wire, CFL lamps, don't throw them to the garbage, carefully remove the lamp from the socket, you will find a tiny pcb with some components, one of them the switching transformer, you can take it appart and use that wire.

               

              There are many other components on that little board that may be of good recycling use.

               

              BTW, I asume that cutting the trace removed the connection to the caps for the SMSC internal regulator, you need to add the recommended capacitance on those pins to ensure proper operation of the internal regulator.

               

              My .02

              -J

              • 184. Re: RG1 1.8v regulator
                morgaine

                That's very impressive work Tooms, well done.  Your list of tests sounds good.

                 

                I wish we had some way of measuring USB data loss directly, such as numbered data injection which we could monitor from the Pi host end.  Networking utilities may help as long as we avoid self-correcting protocols like TCP, but they may exercise only bulk transfers and I'm not sure that observed networking faults will correlate with lost HID events.

                 

                Now that RPF has acknowledged the USB data loss and found a likely cause for it, perhaps someone who isn't banned can recommend that they add logging of those dropped split transactions when they occur.  Logging may not catch all faults like direct monitoring for lost data would, but it could certainly help.  Maybe they do that already in their latest driver?

                 

                Morgaine.

                • 185. Re: RG1 1.8v regulator
                  tmackay

                  Morgaine Dinova wrote:

                   

                  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.

                  Do you think it would be worth tacking on a couple of 100nF caps across C29 in light of this? I didn't think it was worth the effort at the time but it might be important for HF dampening.

                  • 186. Re: RG1 1.8v regulator
                    morgaine

                    Troy Mackay wrote:

                     

                    Do you think it would be worth tacking on a couple of 100nF caps across C29 in light of this? I didn't think it was worth the effort at the time but it might be important for HF dampening.

                     

                    Probably, although I can't claim to have a really solid justification.  We're pretty much in the dark when tampering with black boxes, and we don't really know whether the manufacturer is just designing defensively or has a very specific thing that he wants to suppress.

                     

                    But when in doubt, it's probably a good idea to replicate the manufacturer's recommended circuitry religiously, and those 100nF's are very likely to have less parasitic inductance than C29 so they'll do a better job of decoupling at higher frequencies.

                     

                    If it's a pain, maybe compromise and fit just one.

                    • 187. Re: RG1 1.8v regulator
                      Tooms

                      jamodio

                      >Nice job.

                      Thanks

                       

                      >Quick tip when you need to do "airwire" mods on small pitch components, instead of using wirewrap

                      >or plastic insulated wire, you can use transformer wire

                      yes now you say it, i have hear about the use of the transformer wire but i just forgot it and i was not having any

                       

                      >BTW, I asume that cutting the trace removed the connection to the caps for the SMSC internal

                      >regulator, you need to add the recommended capacitance on those pins to ensure proper operation

                      >of the internal regulator.

                      i have cut the board traces but not removed the caps and i am thinking of just leave them there as they do no harm.

                      for the testing i will add the caps there is showing in the SMSC LAN9512 pdf file and not go for what ever values there is on the board now.

                       

                       

                      Morgaine Dinova

                       

                      >That's very impressive work Tooms, well done. Your list of tests sounds good.

                      Thanks

                       

                      >.....measuring USB data loss....

                      how can you see there is package loss, is there an log file or ?

                       

                       

                       

                      Thanks

                      Tooms

                      • 188. Re: RG1 1.8v regulator
                        morgaine

                        Tooms wrote:

                         

                        >.....measuring USB data loss....

                        how can you see there is package loss, is there an log file or ?

                         

                        That's the problem, there doesn't appear to be any way of directly quantifying loss of USB events, AFAIK.  Adding logging to drivers can help somewhat, but it can never be foolproof since if the driver doesn't detect the loss then it cannot log the problem.

                         

                        This is why I mentioned direct injection of numbered USB packets, for example using a microcontroller board pretending to be a HID device like a mouse or keyboard, which would allow this numbered sequence to be monitored from the Pi end.  Any numbered packet missing from the sequence would then be trivially detectable as lost USB data.

                         

                        Injecting numbered network packets into Pi's network interface might also help (since network traffic flows over USB in the Pi design), as long as the protocol used is not error-corrected (hence no TCP for example).  UDP or ICMP echo should be usable.  However, as I remarked earlier, network packets may not exhibit the same fault characteristics as HID devices if they use a different USB transfer type.  Network error monitoring is extremely useful of course, but may not provide full coverage as a test method for USB data loss.

                         

                        Morgaine.

                        • 189. Re: RG1 1.8v regulator
                          jamodio

                          It is not a scientific or elaborated tool, there are other tools that can be used to generate different streams and types of packets, but this one is very simple and available on any linux distro.

                           

                          If you have another *nix server in your network (has to be preferable in the same segment/switch,) as root you can run the ping program in flood mode, in that mode the machine/interface will try to spit ICMP echo packets as fast as possible, here is an example:

                           

                          root@tango:/# ping -f -n 10.0.2.60

                          PING 10.0.2.60 (10.0.2.60) 56(84) bytes of data.

                          .^

                          --- 10.0.2.60 ping statistics ---

                          38799 packets transmitted, 38799 received, 0% packet loss, time 18693ms

                          rtt min/avg/max/mdev = 0.335/0.439/5.464/0.067 ms, ipg/ewma 0.481/0.444 ms

                           

                          ping will continue to send packets until you cancel the program with control-C and then will report the statistics in the bottom.

                           

                          If you start to loose packets or the "echo" packets don't return after a given time (configurable) you will start to see dots filling the screen.

                           

                          The -f option means flood mode, -n so you don't waste time to resolve the reverse address of the IP address used (that's the fixed IP I assigned to the R-Pi in my lab)

                           

                          There are other useful options like setting the size of the packet payload, or the pattern, etc, do man ping to have the complete list/description.

                           

                          With this simple test is how I found and reported that one of the earlier versions of Debian (not Raspbian) was producing a kernel panic, since I switched to Raspbian I have not tried again to see if the problem was fixed on the Debian distro. Didn't have that problem with Arch Linux, and it seems that the panic was related to the USB driver and the ability to handle properly interrupts.

                           

                          Another example:

                          root@tango:/# ping -f -n 10.0.2.60 -s 1024

                          PING 10.0.2.60 (10.0.2.60) 1024(1052) bytes of data.

                          ..........................................................................^C

                          --- 10.0.2.60 ping statistics ---

                          25974 packets transmitted, 25900 received, 0% packet loss, time 23598ms

                          rtt min/avg/max/mdev = 0.739/0.829/5.947/0.080 ms, ipg/ewma 0.908/0.830 ms

                           

                          In this case you can see that there is no packet loss but given that the payload is larger the R-Pi takes more time to return the echo packet.

                           

                          You can obviously also ran ping in this mode from the R-Pi:

                           

                          root@raspberrypi:/# ping -f -n 10.0.2.24

                          PING 10.0.2.24 (10.0.2.24) 56(84) bytes of data.

                          .^

                          --- 10.0.2.24 ping statistics ---

                          16236 packets transmitted, 16236 received, 0% packet loss, time 11801ms

                          rtt min/avg/max/mdev = 0.383/0.438/1.365/0.045 ms, pipe 2, ipg/ewma 0.726/0.497 ms

                          root@raspberrypi:/#

                           

                           

                           

                          -J

                          • 190. Re: RG1 1.8v regulator
                            Roger Wolff

                            To test character-loss on serial lines I've written a program that's called swirl (IIRC).

                             

                            abcdefghijklmnopqrstuvwxyzABCDEFGHIJLKLMNOPQRSTUVWXYZ1234567890

                            bcdefghijklmnopqrstuvwxyzABCDEFGHIJLKLMNOPQRSTUVWXYZ1234567890a

                            cdefghijklmnopqrstuvwxyzABCDEFGHIJLKLMNOPQRSTUVWXYZ1234567890ab

                             

                            etc. You can see kilobytes of data pass in front of your eyes, but one byte or packet missing and you'll spot it. But programmatic checking is also possible.

                             

                            Put this in a teensy or multio http://www.bitwizard.nl/catalog/product_info.php?products_id=56 and you'll have an easy test.

                             

                            I usually use the ACM class for programs in the multio: I have a virtual com port on both ends, which is convenient.

                            • 191. Re: RG1 1.8v regulator
                              jamodio

                              Reminds me of the "classic" text string for serial communications (you can add the lower case version obviously)

                               

                              THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG 1234567890

                               

                              http://en.wikipedia.org/wiki/The_quick_brown_fox_jumps_over_the_lazy_dog

                               

                              -J

                              • 192. Re: RG1 1.8v regulator
                                Tooms

                                Thanks guys for the ideas for testing the usb issue.

                                 

                                I think the network ping is some thing i will look more into but the serial testing is an good idea but i think it will make my testing to complex and need more gear in the setup, i think it is better to keep it simple for this testing or i will never have it done.

                                 

                                In fact at the time i am testing the switch mode psu modules i have to find what of them is best will do the 1.8v and 3.3v at 50-150mA, but the ones i have now dont seems to be very efficiency at that small load..

                                 

                                The module i am testing is this one: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280939678549

                                 

                                here you can see the efficiency of one module i am testing now and it seems not to be very efficiency at loads in the low end, so if the load from the RPI is only 50-150ma then the efficiency is only 29-55% and that is not good.

                                 

                                 

                                DC Load(A)               Efficiency(%)           

                                0,0100                        7,2210

                                0,0500                      29,4073

                                0,1000                      45,4059

                                0,1500                      55,5899

                                0,2000                      62,4374

                                0,2500                      67,5141

                                0,3000                      71,2567

                                0,3500                      74,2060

                                0,4000                      76,5965

                                0,4500                      78,5389

                                0,5000                      80,1118

                                0,5500                      81,4908

                                0,6000                      82,6600

                                0,6500                      83,5954

                                0,7000                      84,4475

                                0,7500                      85,1550

                                0,8000                      85,7698

                                0,8500                      86,2674

                                0,9000                      86,5859

                                0,9500                      86,6444

                                1,0000                      86,9425

                                 

                                 

                                So i am in the need to find an better switch mode supply, do you know ones that i can get easly ?

                                 

                                 

                                I have got some LMZ10501 but they are one the chips and no board so i have to build them up first, but i think they will be alot better for this low load.... but damm they are small.

                                 

                                 

                                 

                                Thomas

                                • 193. Re: RG1 1.8v regulator
                                  Roger Wolff

                                  Yeah. In first approximation, many switched regulators have a constant current "loss" and then an efficiency for "infinite" current. In your case the "limit" efficiency is about 88%. The constant current can be deduced from your measurements, but I'm too lazy to figure it out.

                                   

                                  You should be able to get an efficient switching powersupply with modern chips. The cheap ones on ebay are built around (copies of?) ancient chips that "work, but are not that efficient".

                                   

                                  I just went to "ti.com", and then clicked that I want a 4.5-5.5 input, 1.8V output, 150mA powersupply. Then I clicked on one of the "most efficient" designs, and got one that should be affordable at "bom cost $1.85".

                                   

                                  In single numbers they cost about EUR 2,- This sounds "doable". I'll see if I can make a small test-PCB for one of these guys this week. (hihi: The 1.8V output circuit is the reference design on page 1 of the datasheet).

                                   

                                  To improve efficiency, it that's what you're after, it would pay to make a 1.85V switcher, and leave the LAN9512 connected to the 1.8V plane. Hopefully that would switch off most of the internal regulator in the '9512....

                                  • 194. Re: RG1 1.8v regulator
                                    pegwag

                                    Hey Morgaine,

                                    As a somewhat related question. . . posible for you to suggest an affordable soldering iron with a small tip-to-grip ratio? Price range around $125 or so? Everything I come across is beaucoup bucks! I have a "hobbiest" iron from Adafruit but don't think it's going to work for me. Since I'm quite interested in this stuff I should invest in something I can use for eons..

                                    Thanks as always

                                    Peg