iXce’s blog

Some of the non-security things that impressed me most at past Chaos Communication Congresses were the Project BlinkenLights-like talks, where buildings were transformed into large-scale pixel screens, enabling random users to control a light matrix spread over the whole surface of the building. From the original monochromatic setups in Berlin, Paris and Toronto to the RGB AllColorsAreBeautiful project in Munich, things have evolved quite a lot, and documentation about how the whole things are done is emerging.

This is why we, at hackEns, started working towards setting up such an installation on one of the fronts of our school dormitories in Montrouge, France (right outside Paris). The first step was obviously to design a working module to lighten each window, producing enough light intensity to do something impressive while still remaining cheap enough to deploy over the whole building (which is basically 6 floors with 8 windows on each floor, so 48 modules altogether). Let’s note that due to the specific structure of the building, our best call is to put the lights outside on the floor of the small balconies we have, as opposed to the previously mentioned projects where the lights were on the inside of the buildings.

Here is how the current module performs :

The module is remotely controlled from my laptop, which is connected to another computer through ssh, which is itself connected through an USB-to-serial wire to a RS485 transceiver which dispatches the commands to the light modules on the bus.
Our current control scheme is to use a tiny PIC10F per window to control each color component through PWM (given the output power of the LEDs, we actually use some transistors in the middle to do the power amplification). The PIC receives its orders on the RS485 bus. Note that since RS485 is limited to 32 receivers, we will actually use 2 RS485 buses with 24 receivers on each bus. The protocol we use on RS485 is quite simple, basically mentioning on a few bytes the module identifier and the three R/G/B components, with a few extra details for correct synchronization.

We tested a bunch of various high power LEDs, from simple 5mm high power LEDs to 3W StarLEDs through some very nice SuperFlux LEDs. Each kind of LEDs had its pros and cons, let’s list a few. The simple ones were really too direction, with a viewing angle of about 15°, so that it is almost impossible to melt the red/blue/green colors into something else. The superflux ones were pretty cool, produced quite nice melted colors, but were really not powerful enough (especially on the red side) so that we would need something between 5 or 10 of them to do something cool, leading to a lot of extra issues and requiring a lot more of PCB space. The StarLEDs are definitely the best on most aspects, a single StarLED produces awesomely bright colors, and a simple sheet of bakery paper is enough to ensure perfect color melting (which is already pretty good, except on the borders of the lightning area, due to the 3 single-color LEDs inside the StarLED being 0.5mm or so away of each other). The only issue with the StarLEDs is that they consume a lot of current, being powered at about 3V/1A. This leads to power supply and security issues, since we do not want to have wires with 50 amps running all over the front of the building. We intend to solve this issue by splitting the power supply scheme into a tree (with one or two branches per floor) and by powering each floor with higher voltages and lowering them to 12V or 5V with a switched-mode power supply on each floor.

The next milestones are to evaluate some cheap StarLEDs from Hong Kong, then to produce a prototype PCB and then to scale up to the building.

There are still a few issues right now, namely the fact that we need to find a cheap way to enclose our hardware to make the whole thing weatherproof, the fact that we need to get the approval of all the people living behind the windows we want to lighten, the approval of our lovely administration, and we need to find the money to find it. While the first three issues are pretty much a matter of time, any help on the financial side is obviously welcome. More specifically, if you know a company which could either provide financial support or hardware support (especially on the StarLED side, which are about 12 euros per LED, and which make it for more than 90% of the project budget), your help is more than welcome.

Window module prototype