you could use the arduino to send osc events (via the ethernet shield, processing, pd, ...) and react in the bge to the osc events.

i wrote a post on my blog a while ago how this can be done
http://www.local-guru.net/blog/2009/03/08/using-the-blendergameengine-as-osc-client

COOOL  

I always wanted to see where the readers of my blog are comming from, so I took a picture frame and inserted a world map, a handfull of leds and an arduino. Some soldering and some rubyscripts later I had my hardware geo-aware logfile visualization.

http://www.local-guru.net/blog/2010/06/05/blinking-logfile-map

@Tijnie

20 eyebrow positions
50 mouth positions
512 shades of color

makes 512000 different smileys :-)

I just finished my Smiley-O-Mat - it's a tin-box with 3 turning knobs that allows you to controll the appearence of a smiley. With 3 simple turns I can now tell your co-workers, familymembers, ... how you feel at the moment and if it is wise to talk to me right now :-)

my blog post contains the processing and the arduino code
http://www.local-guru.net/blog/2010/01/08/smiley-o-mat

This is what the controller looks like


and this are some of my smileys

hi,
it is a knightbright module and i didn't use any resistors because im a complete electronic noob :-)

tnx for your tipp

Hi,

3 days ago i managed to connect a 5x7 led matrix to my arduino
(see http://www.local-guru.net/blog/2009/04/03/5x7-led-matrix-on-my-arduino)

now i managed to solder it to a prototype-shield
http://www.local-guru.net/blog/2009/04/06/5x7-ledmatrix-shield

looks far more professional now (well, as long as noone looks at the wires on the back )

cu guru

because we have an old imac standing on the shelf displaying some rss-feeds, our nagios-network-state and controling some lavalamps showing the status of our continuus integration server :-)

As in any office, my co-workers and I experience several WTF-Situations during our working day. So we decided to implement a simple system to count the WTF's and use them as a metric for our working climate :-)

we use an "emergency stop"-Button which is connected to an arduino. This arduino sends the string "WTF" on the serial line a little python scrip writes them to a file, another processing app count's the lines in the file and offers the result via http, which is read by a processing app for visualisation ...

http://www.local-guru.net/blog/2009/07/03/arduino-based-office-wtf-counter

made a sketch that connects my c-control i2c thermometer module
to the arduino. the module is based on the DS1631 chip.

it was a bit hard to figure out what the datasheet wanted to tell me,
but once i decoded that it was quite simple  

code and a picture can be found at
http://www.local-guru.net/blog/2009/02/02/i2c-thermometer-on-arduino

i wrote a processing sketch to visualize and record sessions on a training bike. i used my arduino, reed-switches and 2 rare-earth magnets to record the pedal rotation and made a little animation of a little figure on a bike.

http://www.local-guru.net/blog/2008/12/08/training-bike-visualization

have fun,
guru