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USB motion sensor (PIR) to wake up screen

Friday 20 June 2014 at 10:13

I have an always on net-book for weather forecast (yeah, when paragliding, you need it)
It basically displays a full screen custom web-page with time and date.

Its always on, not really good for the back-light and energy consumption.

So I got the idea of plugging a PIR sensor to wake up the screen when someone approach it.

Take an Arduino Micro Pro (8€ for the Chinese version), a PIR sensor from eBay (2€), a Hammond case (1€) and an USB A male from scrap (0€).

Let’s give a try, with a basic wiring, and this sketch to emulate keyboard thanks to it’s USB HID, the Arduino Micro Pro is a must.

int sensorPin = 10;
void setup()
  pinMode(sensorPin, INPUT);

void sendWakeUp(void);

void loop()
  if (digitalRead(sensorPin) == 1) 
    while (digitalRead(sensorPin) == 1)

void sendWakeUp(void)
And voila!
Quite nice, discrete and works very well, for about 10€/$.
Note: if someone has an idea to send a key other than LEFT_CTRL (as it can be disruptive on a workstation), I’m looking for a solution.

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Mes trouvailles du jour : 18 June 2014

Wednesday 18 June 2014 at 21:00

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Tuesday 17 June 2014 at 21:00

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Mes trouvailles du jour : 27 May 2014

Tuesday 27 May 2014 at 21:03

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Online case design for laser cutting

Monday 26 May 2014 at 19:42

Case dimensions with finger locking made easy:

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Kobo mini GPS mod with 3D printed case

Monday 26 May 2014 at 12:59


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

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


You will need for this mod:

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.


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:

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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