• PCBs

    marble04/12/2018 at 10:16 2 comments

    Today the PCBs from PCBWay arrived. Upon first inspection I can see no defects. Even the solder mask and silk screen seem so line up perfectly. I'm also glad that the vias are tented, meaning that putting silk screen over vias didn't make the text unreadable.

    Right now I'm waiting for all the components to arrive. I got 11 boards (I ordered 10), but only parts for two protoypes. I depending on how well I don't fuck up the soldering and power supply, I may need to order more parts and SFP modules.

  • Misusing SFP

    marble04/09/2018 at 11:48 0 comments

    What all SFP transceiver seem to provide is the modulation of a differential signal on some medium and the demodulation from that medium to a differential signal. Most SFP tranceiver are meant to interface to some optical fiber, but there also are some that provide yet another RJ-45 with Ethernet.

    I'm interested in the optical ones. Optical fibers have a number of advantages over metal wires, which I already discussed in the projects description. Therefore they are interesting for all kinds of projects. A great example is OneTesla. They use fiber optic transmitters, cable and receivers to isolate the breaker controller from the high voltage of the tesla coil. One could also think of having an isolated USB line to put a SDR dongle on the roof without worrying that a lightning strike might fry your computer.

    Basically right know I'm looking for excuses to build this little side project :D

    But I'm not the only one building silly breakout bords. Even Xilinx is doing it. The Status right now is that I'm waiting for the PCBs and parts from taobao...

  • Spaß am Gerät

    marble04/09/2018 at 11:28 0 comments

    During a shopping spree in Shenzhen I came across a booth that sells optical fiber network equipment. The one thing that caught my eye was a 1000Base Ethernet to SFP media converter. They were sold in pairs for 480RMB (roughly 62€) inlcuding the SFP transceivers. For 10RMB more I also bought a matchting 5m fiber cable. Back at home I tested the device with the laptop of a friend and shure enough, the converters and transceivers can hanle 1Gbit/s.

    marble@archlinux ~ % cat /dev/zero | pv -r | nc 10.10.10.3 1337
    [93.7MiB/s]

     (93.7MiB/s equals 786.0126 Mb/s - considereing the TCP/IP and Ethernet overhead this seems reasonable)

    The power supplies for the converters supply 5V with up to 1A. So in theory one can run these from the USB jack of a modern laptop. One of my goals is to get network across (or through) a lake during a camping trip this summer.

    Being willing to risk voiding the guarantee I opened up one of the devices.
    The board seems to be double sided withno inner layers. Nexto some power supply chips the active components of the board are a 4 port Gbit Ethernet switch chip and a OTP microcontroller

    QCA8334 Four-port Gigabit Ethernet Switch

    http://www.inno-vative.com/uploadfile/cfile/upload/201481410155030.pdfCost-Effective A/D 8-bit OTP MCU

    http://www.holtek.com.tw/documents/10179/11842/HT46R003Bv100.pdf

    Before openening it up I expected no switch chip at all. Wikipedia has quite a good article about SFP tranceivers. Their interface consists of 20 pins. 9 for the power supply. 7 for control (Loss of Signal, detecting that a transceiver is plugged in etc.) and 2 differentials pairs for communication - TD and RD.

    Since Ethernet also works with differential signals (although through current loops - hence the little transformer blocks nexto every Ethernet port) I though one couls simply wire them to the SFP port. Apparently not 😄.