Mittwoch, 16. November 2011

Internet of Things

Last winter i had the idea to add our flat some automation functions. I looked for solutions that were comercially available, but what i found would not thrill me. As i didnt want to put cables into every edge of our flat, i was basically limited to wireless solutions. I found two that seems ok to me: The FS20 system and its successor, called "Homematic". While FS20 has a wide range of different actors and sensors, and is pretty cheap, it has some basic limitations: communication takes place in only one direction, there is no acknowledgment of commands send to an actor. I think this is a bad thing in general, as it may lead to malfunctions. Home automation, including lightning and heating is not where i want to debug communication issues. This stuff simply has to work.
The other limitation is security: FS20 communication is completely unsecured, there is only a "house id" to prevent unwanted interaction with your neighbors devices..

The FS20 successor improves both limitations: It has bidirectional communication and encryption. What detained me from getting the homematic system then was the quite high price tag, the need to buy a special master station and some the design of the thermostats/radiator valve actors. Each rooms needs its own thermostat which then controlls the radiator actors. Adding the cost of the master station i would need to buy, i eventually ended up at a price of several hundred euros just for basics functionality. To much money for just playing around a little bit.

So last winter i decided to build some stuff on my own and did research on what would be a good point to start with. There are a lot of ressources on the net dealing with home automation stuff, but i had some preferences. As i already did a lot of projects using the AVR 8/32bit family of microcontroller from Atmel, i wanted to use one of these controllers. I also searched for solutions that provide many software components (drivers, servers, communications stacks, etc..) ready to use and tested. I know what effort it takes to get software from a quick-and-dirty hack to something useable for a reliable solution.

During my research i stumbled upon many interesting projects. I wont list them all, but some i kept following for some time, e.g. building small wireless microcontroller notes or the Open Energy Monitor

Eventually i got a pack of evaluation board available from and startet with a software package named (badly) "Ethersex"

In the folloing i will describe some of the things i learned when playing aroung with this stuff.

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