Mes trouvailles du jour : 27 May 2014

Kobo mini GPS mod with 3D printed case


XCSoar is an amazing software for sailplane, hangglider and paraglider. But it laked the proper hardware with the following features:

  • sun readable ( eink)
  • usable with gloves (anything but capacitive)
  • long battery life
  • running android/linux
  • GPS and/or bluetooth
  • dirt cheap

The Kobo Mini (unfortunately no more retailed) appears to be meeting all theses requirements exept the GPS.


You will need for this mod:

  • Kobo Mini reader
  • GPS module with serial output
  • switch (optional)
  • extra battery (optional)
  • of course an iron solder, solder wire and a piece of flat ribbon cable

Take your original Kobo Mini:

(By the way, the way Kobo handle the first boot is just crap: I don’t want to register my device online or anything, just to drag and drop my own ePub books)

Backup the micro SD card (command for linux only, sorry)

dd if=/dev/mmcblk0 | gzip > ~/kobo.img.gz

Solder the MTK3339 GPS breadboard (with a piece of flat ribbon cable such as IDE, Floppy, etc..)

KOBO to GPS MTK3339 wiring

TP2 <-> BACKUP (TP2 is just below the battery connector)
RX  <-> TX
TX  <-> RX

Don’t forget to cross RX<->TX and TX<->RX

Just in case you wondered, yes the BACKUP does accept 4.2V, not just 3.3V (have a look on the MTK3339 datasheet )

The spacer from Thingiverse (thanks to matbhe for the design) printed by Shapeways for just 22€ incl P&P in about a week.

Take the screws, M1.6x7mm (my 10mm were too long, I had to cut them with a pair of pliers)

All fit snugly, even the original back cover.

Looks nice, no?

Add ON/OFF button to switch the GPS power (a simple SMD switch to the GPS’s VCC)

So I can still use it as a regular eBook without draining the battery and without the blue led blinking in the dark.

A piece of double side tape holds the module in place.

The switch is accessible with the nails as it’s quite recessed.

Add a label for even more clarity.

The original battery of 1000mAh gives from 4 to 6h, which can be quite limitating.

I added a 4000mAh battery from AliExpress:

I removed the original one and harvested it’s connector for the new one.

It’s held firmly with double sided tape and now it last about 20hours of flight: perfect. (but the drawback: it is quite heavy to read in the bed now….)


Download XCSoar KoboRoot.tgz:

And the maps:

Download hotspot (probable thermal) as waypoints (wpt format), and set the file in waypoints configuration):

GPS configuration

Configure the GPS to /dev/ttymxc0 at 9600bauds and “GPS waiting for fix” should appear, note that the first fix can take up to 15min (30s later on, thanks to BACKUP power supply to keep the RTC and ephemeris)

And here you are, you have a comp GPS for less than 100€/$/£ for paragliding/sailplane, in about an hour of work.

Next update to come is Integrating a variometer such as leBipBip (solar variometer for 89€) would be perfect, as the firmware is opensource (Git) and it as serial connection on the board with NMEA pressure output:

leBipBip PCB board has a 0.05″ header with VCC,GND,RX,TX on the top left side

Misc links

XCSoar forum:

GPS mod found on the internet:

M1.6×10 screws:

Commercial GPS mod base on this device:

XCSoar forum about this mod:

Bigger battery, 4200mAh:

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