UPDATE: upon reflection, I could actually just hack an Classic 4 prototype from work to do all of the storage (it has some flash memory) and message writing (using keypads) and sending (would be done over serial link to the arduino / radio transceiver rig)! Note: there is also a wifi link for internal communications.
Another idea about shorter range personal messaging over the 805.14 link.
This is a slightly edited re-post of a comment I left on Kal's Blog: http://www.invaderzone.com/
What do we understand by the term: 'off grid'? I reckon it means:
-no power grid
-no mobile phone service/signal
-no telephone service
-no internet
I think we should have a backbone of communication that does not rely on Internet i.e. a radio based network so we could, say, send data over radio links. I suppose this would be very useful if the internet or mobile phone networks went down or just generally for fun!
#20-very-low-powered-messaging-service
It would send things like SMS messages over standard radio links using minimal power. So the first thing to say is that means we probably wont use a desktop/laptop because they are power guzzling beasts.
I reckon the minimum hardware needed to do the job is as follows.
Core Specification:
1 x arduino
1 x storage card e.g. SD
1 x radio transceiver
1 x hacked ps2 keyboard
1 x small LCD screen
1 x solar panel
1 x battery bank
this would give the basic hardware platform to send and receive and store messages completely 'off grid'.
optional specification:
1 x ethernet shield for arduino
this could allow a full webserver to be run on the system. Now that would be interesting!
e.g.
http://www.flickr.com/photos/boolean/3399075841/in/photostream/
http://www.flickr.com/photos/boolean/3399886646/in/photostream/
There are several conflicting goals when sending data over a radio link like this: reliability, processing, modulation techniques, security and efficiency etc.
The ideal outcome would be twofish / blowfish / some equally insane encryption on a 100% reliable link which consumes the least amount of power possible. Well this is just not going to happen- firstly, it is virtually impossible and would take an absolute genius if not a team of geniuses to pull off. So I think we should have a more modest initial goal:
Get the link working (unsecured, not optimised for low power)
Later development would consider the following issues:
Issue 1:
The system is powered on all the time?
Solution 1:
Scheduled communication.
Issue 2:
Time synchronisation between transceivers.
Solution 2:
Send SYNC packets between the transceivers.
Most watch crystals drift at 20us/second so we could use that as a starting point to work out the optimal sync period.
