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PPS-GPS cape for the Sensorgnome

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          adafruit_pps_gps_on_BBB.jpg       adafruit_pps_gps_SMA_adapter_cable_and_powered_antenna.jpg

    2014 Sept 15: Software Support

    To make this GPS work (whether DIY or the version from compudata.ca ) you must:

    • image the beaglebone with the 23 May 2014 release

    and then:

    • update the beaglebone with the 10 Sept 2014 update.  (This update requires two reboots to take effect; the software version
      on the web interface will still display as 23 May 2014, but you will see the GPS cape in the device list; it appears
      as a Compudata PPS GPS cape, even if you made it yourself!)

    See this page for details.

    Summary

    This uses the Ultimate GPS Breakout Board v.3 (earlier versions don't have PPS) from adafruit.com, and a powered GPS antenna.
    This unit works with the SG, but we have not field tested it yet.  It will likely be the recommended GPS for
    sensorgnomes, superseding the previous recommendations.

    Parts List

    Note: a (different) premade GPS cape is also available here, but we have not tried to acquire or test it.  We ordered
    and tested one, but it was dead on arrival, and we have not pursued this.
    It claims to work with the same operating system used by the SG (Debian Wheezy), but will probably need some tweaking.

    Advantages over the MR350P PPS-GPS and/or the BU-353S4 USB GPS

    • slightly lower power consumption (0.1 to 0.2 Watts) in usual situation where funcubes are attached via a USB hub
    • significantly lower power consumption (2.8 Watts instead of 4.0 Watts) when used with a single funcube attached directly
      to the beaglebone and no USB hub (most of the savings is from removing the USB hub).  This hub-less configuration was
      not possible with previous GPS recommendations, which all required a USB connection.
    • cape mounts directly on BBB - no additional black box
    • faster to get GPS fix and PPS signal (vs. MR350 PPS-GPS)
    • slightly higher time accuracy (slightly under 1 microsecond sync to GPS/UTC time) than MR350 P; much higher time accuracy than BU-353S4
    • battery-backed realtime clock, so even if no GPS fix can be obtained, SG clock is set to correct date and time
    • simpler to build (especially with the breadboard cape)

    Disadvantages:

    • requires a larger beaglebone case like this or this

    We haven't updated the sensorgnome software to use this GPS automatically.
    Anyone wishing to use it should contact us to prompt an update.
      See above.

    Assembly

    • solder the included battery holder clip to the back side of the GPS breakout board.
    • trim the included pin header to 9 pins
    • solder the 9-pin header onto the back side of the GPS breakout board
    • remove the adhesive backing of the breadboard and stick it on the cape PCB, with the breadboard 'trough' parallel to the long axis of the cape
    • plug the breakout board into the breadboard, so that the 9-pin header is parallel to the breadboard trough
    • make the following connections with wires of appropriate length (included in the breadboard kit):
       
    Pin # of P9 header on Beaglebone Pin Label on GPS Breakout Board Pin Function
    3 3.3V power supply to GPS
    11 TX receive line on /dev/ttyO4 serial port
    13 RX transmit line on /dev/ttyO4 serial port
    15 PPS pulse-per-second; high accuracy sync. pulse
    46 GND power return line for GPS


    Manually Enabling Adafruit PPS-GPS on the SG (until supported by sensorgnome software)

    Copy the attached kernel overlay file ttyO4_armhf.com-00A0.dtbo into /lib/firmware.  Tell the slot manager you want
    to enable the serial port specified by this overlay:

    echo ttyO4_armhf.com > /sys/devices/bone_capemgr.9/slots
    

    Create a symlink from /dev/ttyUSB0 (which was the location for previous GPS devices) to /dev/ttyO4:

    sudo ln -s /dev/ttyO4 /dev/ttyUSB0
    

    Restart chrony, the clock synchronization program:

    sudo /etc/init.d/chrony restart
    

    This has to be done on each power cycle, so could be placed in an init script.

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    FileSizeDateAttached by 
     adafruit_pps_gps_on_BBB.jpg
    adafruit GPS breakout board on prototyping cape
    855.31 kB19:24, 18 Apr 2014adminActions
     adafruit_pps_gps_SMA_adapter_cable_and_powered_antenna.jpg
    adafruit GPS breakout showing connection to powered antenna
    863.9 kB19:24, 18 Apr 2014adminActions
     ttyO4_armhf.com-00A0.dtbo
    kernel overlay file to enable ttyO4, used by the Adafruit PPS GPS when assembled as described above
    1027 bytes00:20, 19 Apr 2014adminActions
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