We control an interactive Christmas tree on the lubrication tram

Last year we built an interactive Christmas tree in the lobby of ČVUT on Charles Square, and this year we were approached by TechNet, who asked if we wanted to put our Christmas tree on the back of a lubricating tram so that anyone could have fun controlling it. Yesterday, in collaboration with the Prague Transport Department and slowtv.cz, it was officially launched.

More about this can be read on TechNet: Na pražské tramvaji jezdí zvláštní vánoční strom. Rozsvítit ho musíte vy, you can watch and control the tree in the comfort of your own home here Právě teď: mazací tramvaj jede Prahou and you can catch up with the tram here on the mobile web OvladejStromek.cz.

On the tree is a chain of individually addressable RGB LEDs (WS2811), which are controlled by the Raspberry PI 2. The flashing of the LEDs is not just random, but is governed by the wave equation simulating waves propagating along the light chain. Anyone can influence this virtual environment with their own unique "wave" sent via the web interface, and tree color patterns are formed by everyone together.

"So much work for such a stupid thing", was how it sounded in my head many times during the project, but we believe it was worth it.  Even when the system was almost ready, we had to make significant adjustments.  For example, we went around the depot with an oscilloscope to measure the noise power. We had to prepare the hardware for the winter and outdoor environments – it can now even be completely immersed.  The software had to be adjusted to keep the connection with the lubrication tram, and it also needed to withstand frequent switching on and off.  It endured major adjustments the day before switching on because our original solutions, designed to operate in our lobby, would not stand up to the rush of users across the whole country.

Tree designers Jirka Zemanek and Martin Gurtner would like to thank (besides their tolerant partners!) all staff at the Department of Control Engineering, who contributed towards the successful execution of the project. Thanks to Ales Kapica and Martin Samek for their IT support, for advice and help with Linux from Pavel Pisa and to Filip Kirschner for developing the web interface. Also thanks to our master mechanic, Ladislav Cmelik for his work on the mechanics, and to our leaders Zdenek Hurák and Michael Sebek for their support and, indeed, to all of you, for it is thanks to you that our department can do such things.

Merry Christmas! :)