Kobo mini GPS mod with 3D printed case


XCSoar is an amazing software for sailplane, hang-glider and paraglider. But lack 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 (yes 50€/£/$ for this hardware is dirt cheap)

The Kobo Mini is a very good eReader (unfortunately no more retailed) appears to be meeting all theses requirements except the GPS.


Component list

You will need for this mod:

  • Kobo Mini reader
  • GPS module with serial output or a BlueFlyVarioTTL
  • 3D printed spacer
  • extra battery
  • iron solder (a good one, I use this)
  • solder wire and a piece of flat ribbon cable

( By the way, the way Kobo handles the first boot is just crap: no I don’t want to register my device online or anything, just to drag and drop my own ePub books, thanks! )

GPS module instructions

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

KOBO to GPS MTK3339 wiring

KOBO - MTK3339
TP2 <-> BACKUP (TP2 is just below the battery connector)
RX  <-> TX
TX  <-> RX

Don’t forget to cross RX<->TX and TX<->RX (the eternal embedded engineer question, RX TX….)

Just in case you wondered, yes the BACKUP does accept 4.2V (TP2 is battery test point, so not regulated), and not just 3.3V (have a look on the MTK3339 datasheet)


You can download the STL of the “Kobo mini Case Spacer II” on Thingiverse

And download the gps cover

The STL (in mm) file is then printed by Shapeways for just 22€ incl P&P, delivered in about a week: very cool!


You will need 5screws, size M1.6 and 8mm (my 10mm were too long, I had to cut them with a pair of pliers)

All fit snugly, even the original back cover.

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.

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

Add a label for even more clarity.

BlueFlyVarioTTL instructions

Or this set for the BlueFlyVarioTTL, download the cover: And download the spacer for the battery:

The file STL (in mm) is then printed by Shapeways for just 19€.

You will need 5screws, size M1.6 and 8mm (my 10mm were too long, I had to cut them with a pair of pliers)

Solder 0.1″ header

And remove the black plastic from the header

Drill 5 holes with a 1mm bit, using the module as guide

Insert it

Then solder the 5 wires

Use 2 parker 3mm screws

That’s it

Battery for GPS module or BlueFlyVarioTTL

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

The original 1000mAh beside the new 3800mAh battery

The new battery li-ion from AliExpress measure 4x75x86mm, with 3.7V and 3800mAh. Warning, you need the 3D printed spacer to use this battery.

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

To remove the original double side taped battery, use an air dryer or so (warning not a hot air gun, it would be too hot)

The new battery is 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….)


They are tons of tutorials on the web, I wont describe it any further, but simply put, it works this way:

Download XCSoar KoboRoot.tgz: http://www.xcsoar.org/download/data.html

And place it on the kobo root file system using any file browser, restart and you are done.

GPS configuration

GPS module

For the GPS module, set the device to /dev/ttymxc0 at 9600bauds, generic drivers.


For the the BlueFlyVarioTTL, set the device to /dev/ttymxc0 at 57900bauds, blueflyvario drivers.

“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)

You can change the sink alarm and volume:

  • Enable Wifi, and Telnet,
  • Connect to with telnet to the Kobo,
  • send the following commands:

stty ospeed 57600 ispeed 57600 -F /dev/ttymxc0 #configure baudrate

stty -F /dev/ttymxc0 raw #set device as raw

echo ‘$BFS 2500*’>/dev/ttymxc0 # sink alarm to -2500cm/s

echo ‘$BVL 70*’>/dev/ttymxc0 # volume to 70%



Then download the map: http://www.xcsoar.org/download/data.html

Download hotspot (probable thermal) as way-points (wpt format), and set the file in way-points configuration): http://thermal.kk7.ch/, save all this map file to the correct XCSoar folder.

I created custom map content to have paragliding skyways displayed on XCS:

More detail here: http://www.dotmana.com/weblog/2014/07/xcsoar-generate-custom-maps/

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

Result with GPS module

Result with BlueFlyVarioTTL

(note the green led flashing when lifting)

leGPSBip: solar vocal GPS alti vario

This device is ready to use with the Kobo or any smartphone, simply connect it and voila! You have a fully GPS/altimeter enabled smartphone.

It also act as a standalone vocal GPS variometer when not connected, pretty convenient:

More info here: http://www.lebipbip.com/legpsbip-solar-vocal-gps-alti-vario/

Links and references

XCSoar forum: http://forum.xcsoar.org/viewtopic.php?f=3&t=1242

Kobo GPS mod on another blog: http://www.extreme-nature.de/?p=9114

M1.6×8 screws: http://www.ebay.co.uk/

Commercial Kobo mod: http://www.goflyinstruments.com/gofly-project-v4/

XCSoar forum about this mod: http://forum.xcsoar.org/viewtopic.php?f=3&t=1404&start=10

Li-ion battery on AliExpress: http://www.aliexpress.com/item/L002-3-7V-3800mAH-457992-PLIB-polymer-lithium-ion-battery-Li-ion-battery-for-tablet/1477811584.html

BlueFlyVarioTTL http://blueflyvario.blogspot.com.au/2014/11/blueflyvariottlgpsv10-released.html

BlueFlyVarioTTL case: http://blueflyvario.blogspot.com.au/2014/07/blueflyvariottlgps-simple-case.html

Mini Solar vario: http://www.lebipbip.com/

STL archive: Kobo_Mini_case

47 thoughts on “Kobo mini GPS mod with 3D printed case

  1. It’s about 4 to 6 hours of flight with the original 1000mAh.

    And more than 20hours with the new 3800mAh.

  2. Hi,thanks for your instructions on this hack.Would it be possible for you to provide some software instructions for installing xc soar on to to the sd card . Are we limited to a 2 GB card ? Can I use the same instructions and files for the go fly v4 software installation? I have ordered the hardware and case and would appreciate some guidance before I commence .

  3. Sorry, said in this post, I don’t want to cover the software part as it’s widely detailed online (use google)

  4. Hi friend, can you send me the model of this hack to print here in my 3dprinter? Thanks

  5. Hi, I want to print a case for my kobo.
    Would you share your fail for the 3dprinter?
    If you have it it will save me a lot of time drawing it myself!

  6. Shapeways asks what dimensions were used in making the STL files for the spacer…is it inches or millimeters?

  7. Great!. Thank you. I did it and it works fine.
    Two little modifications. I do not connect the back up cable and it gets “GPS fix” in one minute, and the second I had to cut the internals “walls” of the back cover to install the new and bigger battery.
    Do you know how install other adroid software? like Oziexplorer, Navionics, etc

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  9. Hi Tweepy, thank you for the nice tutorial. I already purchased a second-hand modified Kobo Mini and trying to set a new one for my friend. I purchased from the Australian producer the new BlueFlyVario_TTL_GPS_v10 (http://www.blueflyvario.com/index.php/buy) which include both GPS and Variometer and that is larger than the GPS chip you used. I 3D printed the relevant minicase shape (http://blueflyvario.blogspot.it/2014/07/blueflyvariottlgps-simple-case.html?spref=fb). But I like the idea to integrate a 3800 mAh battery but I have non capability to modify by myself your shape in order to space the case and at same time to host the new VARIO/GPS. Is it something that you can do? Thanks

  10. Actually, I’m currently doing what you are looking for: battery + spacer with blueflyvario + case.
    Give me a week and I’ll add it to this tutorial. (meantime, you can look at the spacer without GPS)

  11. Hi there, I notice that the original battery appears to have some circuitry in it, whereas the new battery does not. Does anyone have any idea what the circuitry does? I assume it is battery maximization, but I’m unsure whether to migrate it across to the new battery – given the difference in use cases.

    Has anyone looked into this?


  12. The circuit on the battery is the over/under-charge and short-circuit protection. You should have one on every battery as Li-Ion are pretty sensitive about theses issues. For single cell battery, it’s simple: you may try to fit the old circuit protection to the new battery respecting the polarity

  13. Hello,

    I cant find that type of screws. Can you tell me where did you purchased them?


  14. Hey!

    I’ve just ordered about the last Kobo minis in this world 🙂 and I want to modify them with a bigger battery, bluefly etc.

    Just some questions:

    1. Do you know that spacer? I like it a lot more than other designs: http://www.thingiverse.com/thing:682337

    2. Did you remove the circuitry from the original battery and move it to the new one? Looks like it from your pictures. Is it some kind of protection?

    3. Is the bluefly slower / less resolution than the leBipBip?


  15. 1 – yes, a friend of mine uses it, it’s fine
    2 – yes, I kept the protection circuit from the orignal (overcharge, overdischarge, short circuit)
    3 – the BlueFly vario is slightly slower to respond that the leBipBip

  16. Hi!
    Thank you for model.
    Can you give me step-file the cover and the spacer for the battery please?
    I just want upgrade this things for me.
    I can’t convert STL to STEP-file or file for SolidWirks. 🙁

  17. Hi! Awesome post, helps me in my journey on converting my mini to a big batteried bluefly beast. I just read the post by Raphael and your reply on that. Regarding the batteries protection print.

    The chinese battery I bought only has a very simple print soldered to it. It seems to be just a pass through for + and -.

    I understand that you moved the small print on the original battery to the larger battery? Is this essential? Or am I misunderstanding this? Also are there any dependencies on this to work? Or will that protection pcb just work on most other lipo cells?


  18. Have you had or heard of anybody joining the old battery in serial to the new battery and using the connector with both batteries connected? just to get a few extra hours use?

  19. sorry, I meant setting the two batteries up in parallel and then to the connector?

  20. I would not do that: lithium-ion batterie are pretty sensitive in term of voltage/current rating, each cell has to be indivially connected to a controller, meaning it has to be in serial, then you need to reduce the voltage as the device is designed to handle a single cell.
    Best to stick with a large single cell.

  21. The over/under voltage protection circuit board (the one you are calling ‘print’) has to be present for any li-ion battery.
    If the new large one doesnt have one, simply swap it from the previous battery. Of course the overcurrent protection will be lower than the new battery is really capable of, but who cares, as the charging circuit (from the kobo) will remain the same.
    BTW, the charging time with the large battery is about a night 🙂

  22. Hi again,
    The link you posted to the battery is not the same as the one in your blog. It reads that its 5000mha and the dimensions are different. It has probably changed since you posted it?

    I ordered one with the dimensions you posted up but when it arrived its only a lithium polymer batter not Lion. Would that battery be no good or would it work just not as well?

    Thanks for all your help

  23. Dr Swan.

    I Ordered that battery. Its 5500 Mah actually ( according to the sticker ) and it fits! Its just as thick as the original one from the blog. Just a bit wider and taller. And it actually does come with a protection circuit ( unlike what I posted before ) so you can just swap the battery cables and it’ll fit. 1700 mah more ( if the sticker doesnt lie ) than the one on the blog!

  24. Thank tou for this magnific post!. This is the third I did. Previous: Lost, found, fallen, sold…. I am in love with this aplication in gliding.

    With this new Kobo I have a problem. Once the software (Top Hat) is loaded, the “PC connection” does not work. This problem is related in some foros and there is a procedure to change the original Kobo software for anotherone, which permits to the Top Hat the “PC connection”, but this does not work me.

    Do you know anything about this?

  25. Thanks for your post. I am in fact waiting for the bipbip…I still have to load the xcsoar in tne Kobo.

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  28. Everything is fine as this is definitely not a mecanical part: FDM or sintering process with ABS or Nylon material

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