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I really wanted to call this entry: "Chibi Meets Mr. Dislocated Green Thumb: Or, How to Suck a Bit Less and Gardening", but it didn't quite fit in the title.  In any case, gardening isn't exactly a topic you find on most engineering-centric sites ... but since I'm determined to try not not to kill every green and leafy thing that I come into contact with this year, I thought I'd try to compensate for my decidely non-green thumbs with technology.  How am I going to do that?  With a bunch of RF transceivers, sensors galore, and a gratuitous graphical desktop-based data logger of course!

We recently published a couple brief tutorials on Chibi, a light-weight, open-source 802.15.4 stack from Freaklabs.  Chibi is wonderfully easy to use, and the AT86RF212 is a perfect match for this project since 868/915MHz provides excellent range and signal penetration (compared to 2.4GHz), and can safely make it through brick and concrete walls into the house or apartment. 

We're just doing some final testing on an LPC1114-based wireless transceiver we made with this project in mind.  They're relatively small (~3x5cm), and are designed to run off small 1200mAh LIPO cells.  They have an on-board temperature sensor for accurate analog conversion of non-linear temperature-sensitive devices, and we've broken out the I2C pins, 4xADC inputs, and UART so that a variety of analog and digital sensors can be connected and logged.  The UART is convenient since it provides a means to communicate directly with the board, update the firmware via ISP, or figure out why something isn't working.

The idea goes something like this: We'll have one central PC-connected 'Garden Monitor' acting as a hub (based on the LPC1343 Reference Design with an AT86RF212 antenna attached), which will receive all incoming messages and data, logging and manipulating it as required.  Complimenting this will be numerous battery powered sensor nodes out in the garden (see the photo above) checking things like soil humidity, ambient temperature, and the amount of sunlight being received per day.  The communication will be largely one way -- from the sensor nodes to the hub -- since the nodes will spend most of their time in deep-sleep mode to conserve battery power.  They'll take sensor readings at appropriate intervals, and every 15 minutes or so send the collected data to the hub and check if there are any relevant messages waiting for that specific node.

In theory, we'll have one node for every type of plant (since they all have different requirements and are in seperate containers), and can monitor the key information on the PC or via alerts on a simple webpage or via twitter <sigh and roll eyes here /> or something similarly already-been-done-2.0.

We're just finishing off the HW and the firmware for the devices, and have been writing drivers and lookup tables for things like the Vegetronix Soil Moisture Sensors and some analog and digital sensors for ambient light, etc.  Once the HW has been tested a bit more, and we have a chance to start working on the SW client we'll add a new project page with all the files.  We'd like to try to make something as generic as possible to allow people to log any kind of information later on.

In any case, we'd be glad to hear what other people might like to see in an open-source wireless data logging system like this. It has a lot of fun-factor potential, but can probably be quite useful as well. Feel free to drop us a line and let us know what you think!