The LEDs are on the wall

22 July 2010

I’ve officially begun my residency at Eyebeam Art + Technology Center in NYC:

[ Eyebeam bio ]

Working with Hernani Dias on the Re:Farm project (see my previous post for some more info about the Re:Farm project), my first objective is to create the PCB for the Re:Farm On The Wall module, a data visualization module using an LED display to present data away from the computer screen.

[ details after the break ]

Here’s Hernani’s original sketch for displaying the soil moisture level from 6 sensors:

This design uses 7 LEDs to display the soil moisture level for each of 6 sensors (42 in all). The design concept has been formalized as seen below:

The module still has 7 LEDs for each sensor (or farm/garden), but with the addition of LEDs between the groups (for a total of 48) to create a complete circle which can be used with other templates, such as the one below, for visualizing other data such as temperature or humidity:

Ideally, the board will also incorporate a stepper motor to drive a needle (like a speedometer) for an additional data channel.

I’m going to first concentrate on the LED display. Since the board will make use of an ATMEGA microcontroller (Arduino) chip and an XBee radio (to receive the data), real estate on the approx. 3″ x 3″ board is already a bit tight, so I am currently researching Charlieplexing, an LED driving scheme which allows N*(N-1) LEDs to be directly driven by N pins of the microcontroller. 8 data pins from the microcontroller can thus be used to control the 48 LEDs since Charlieplexing with 8 pins allows control of up to 8*7=56 LEDs.

At The Next HOPE conference this past weekend (blog post about the conference forthcoming), Jimmie P. Rogers was demo’ing and selling his LoL (Lots of LEDs) Shields for the Arduino. He has a great post about his work with Charlieplexing which I’m currently consulting. Talk about serendipity!

In a way, the overlap between the needs of Hernani’s project and my own interests in lighting and internet-enabled lighting fixtures is serendipitous as well.  It’s great to be working on a project that is seemingly so diverse from my own projects, yet has so much overlap on the technical side.

It’s also been interesting to observe Hernani’s design approach/philosophy which stems from his graphic design background.  It seems like everything starts from the aesthetic: the documentation for the project has some of the nicest component diagrams I’ve seen; and even his calendar is created in Illustrator ;)

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