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While relaxing on a beach in spain back in 2006, an idea came into my mind. i wanted to build an LED display. fullcolor and large. no large resolution, just large in terms of dimension. in december 2006, i made actual plans for the project. from there on, i experimented, prototyped, programmed and soldered from time to time. having no deadline made it a real long time project. but then in 2009, i had my 10×10 pixel RGB LED matrix, a square meter of color and light.

matrix with its creator

i guess most of you are particularly interested in some facts about the hardware and software. first the hardware. i used 100 Superflux RGB LEDs with an angle of radiation of about 100°. the LEDs are dimmed via 8-bit PWM, generated by ATmega8 microcontrollers. each controller is responsible for 4 LEDs, which makes it a total of 25 controllers, running at 14,7456 MHz. there are 4 controllers on each PCB, the outputs are amplified by darlington arrays.

guts of the matrix

every LED has it’s own small board, including resistors for each color channel. the pixels are separated by a grid made of 4mm plywood. the light in each pixel is diffused by a small piece of air filter material and the frosted plexiglas pane. diffusion was a major problem, and i guess it’s not really possible to achieve perfect diffusion. my solution is a tradeoff between good diffusion and complexity.

pixels seperated by a grid

the data comes from a PC via RS232(USB adapter) at 460800 baud. all controllers read the RS232 line simultaneously and are addressed by a reserved byte in the data stream. so i broadcast the data to all controllers and each one picks the data it is supposed to read. i’ve reached frame rates beyond 100 FPS.

the final software was written in JAVA because of the OS independency. it is still in development and will probably always be. at the moment it is capable of playing back animations which are stored in bitmaps, displaying the game of life and some variations of it, simple particles and several colorful effects and filters. and of course multiplayer tetris with overlaying playfields. can drive up to three sane persons really nuts.
the matrix was always supposed to be some entertaining decoration element, so it has to be able to generate an endless variety of content without steady user inputs. so i let the software surf the internet and jump from link to link. on every website, it collects content. at the moment, its just an image of the whole website, but i plan to analyze for example the text on the website. the image of the website is analyzed to get it’s n main colors, which are then the basic colors of graphical effects. i hope to end up with some kind of AI which analyzes the web in-depth and shows a simulated creative behavior in dealing with forms, colors and movement. but that’s an utopia right now and it’s gonna be a long way.
another plan was to add some kind of interactivity, but the design is not optimized for adding sensors. maybe a webcam could be used as a proper input-device.
future plans for the hardware include the integration of a netbook to have a completely standalone device which connects to the internet via wifi or ethernet. i considered some embedded solutions, but as old netbooks get cheaper and cheaper, this would be a reasonable solution

if you want to have detailed information about the development and the building process of this project, please visit the project’s own blog
http://rgb-led-matrix.blog.de (german)

Spending some time optimizing my prototyping-tools, i finally got the atmega8-basic-circuit i searched for. i don’t need things like onboard MAX232 or FTDI, because i have modules for that. what i wanted was some AVR-module that is robust, compact and features a crystal, a pullup and ISP. here it is:

brickAVR lit

i soldered a row of female pin headers directly to the AVR-pins. they have a distance of 0.4″, so you could fit a custom protoboard-shield on top of the module. a 16 MHz-SMD-crystal was glued under the chip and connected to the pins, and so was the pullup. i glued an 6-pin ISP-header to the front of the chip and connected it to the appropriate pins. last but not least  i added an SMD-LED to indicate power-on.  that was it for the electronics. next i filled the space between the female pin headers and above the atmega with hotglue (sticking the led into it). finally i needed a case. i had some lego bricks lying around on the desk and more randomly picked one that seemed to match. amazingly it fit perfect after i clipped the sides of the ISP-header. so i glued the circuit into the hollowed brick and added a label i made in corel draw. that’s about it.

the module is powered by the programmer (USB) and i can access every single pin. i like to use it in prototyping applications where a whole breadboad would be overkill, fragile or simply too large. like when you  just want to create a specific output signal. the module also easily hooks up to a breadboard. here’s another two pics of the lower side and the raw circuit:

While messing around with twi (that’s what atmel calls i2c) some time ago, i built this little device that does nothing more than listening to the bus and display all the bytes it receives on a two-digit 7-segment-display in hex-format. the motivation for this project was not only “i need this thing” but also “i’m tired of coding and want to solder something. and i have to get rid of these displays anyway”. the schematic and layout was done in eagle. an atmega8-controller (overkill) handles bus and display. the whole device is powered by the bus.

here’s two pics:

top side of i2c-slave

bottom side of i2c-slave

yes, i forgot one line 😦

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