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An open-source marine chart plotter

The goal is to build a low-power hardware which can run OpenCPN (http://opencpn.org/). The main display will be indoor, but the unit will later be expanded to provide usefull informations to outdoor displays. It will also integrate informations from external sensors (wind, or magnetic heading), and from an AIS receiver. MOB trigger from outdoor buttons is also an important feature which will be added. Ultimately, an automatic MOB alert will be triggered when a sensor detects a missing crew member.

hardware design

To keep power requirements low enough, a ARM SoC is used. I did my first tests with a beaglebone black and a 12" touchscreen. My conclusions was

• although OpenCPN can make use of the touchscreen, it's not so easy to use and some operations still require a mouse. Also, the touch screen may be difficult to use in harsh conditions. On the other hand OpenCPN can be driven from keyboard quite easily.
• The beaglebone black lacks CPU power for the task.

I then tested with an A20-based Cubieboard and a HDMI display, and found that this was good enough. So I need a A20-based computer, and a display.

I found that Olimex (olimex.com) has a 15" full-HD display and a few A20 board, and everything is open-source hardware designs. So I selected this display, and the A20-OLinuXIno-LIME2 board. The LCD-OLinuXino-15.6FHD backlight requires 5V power supply, but looking at the schematic you see that this 5V input goes to a boost converter to provide the LCD with 10V. Also, the LCD's datasheet says that the backlight can take between 6 and 21V, so it could be powered directly from the +12V battery. For this you just need to change the "Jack_10V_DC" jumper (actually it's a solder pad on the board) and remove C7 and C8 which are rated for 6.3V only. Everything else will accept 12V and the boost converted will just go to sleep.

From my experiments, the LCD backlight will need at most 5W, and the LIME2 also at most 5W with LCD on and both cores busy. With LCD off the power requirements is between 1W and 2W, depending on what OpenCPN is doing.

There are 4 custom boards in the project. The most important one is "marine_gps" which provides 5V to the LIME2, and offers interfaces with a GPS module and outside equipements. See the page "marine_gps board" for details.

There is also a small board (connect_board) with connectors, connected to the marine_gps board with HE10 connectors. The point is to be able to easily disconnect and remove the chartplotter (e.g. to do software developement at home). It also allows to feed the DSC VHF from another GPS with just 2 jumpers move.

The third board (gps_module) is where the GPS module is plugged into. It's connected to the marine_gps board using a flat cable and HE10 connectors. It will be installed at the top of the enclosure, but it could also be moved outside the enclosure if needed. I choose a module based on the MTK3339 chipset, for its low power requirements and good sensivity. The integrated log could also be usefull in the future. This board is for the Microstack GPS module from element14. A local 3.3V LDO regulator will provide the module with a stable power supply. The Adafruit ultimate GPS module could also be used but it's more expensive.

The last board holds 5G MEC switches. One of them (with a red/green LED) will be for power control, the others provide inputs to the A20 via the LRADC0 interface with appropriate resistors.