Posts Tagged: LEDs

The ‘Schollenspiel’ – more LEDs than you can count

tldr; In 2015, the student representatives for electrical engineering at RWTH Aachen university rebuilt an awesome childhood game.

While I was studying at RWTH Aachen University, I was part of the student representatives for electrical engineering (FSET) for a few semesters. We were elected each semester and besides representing the students in different bodies within the university, we were in charge of welcoming the new students. Luckily, a fund from the university allowed us to spend money specifically for the new arriving students each year for things like building games, renting an inflatable human-soccer-field or having a BBQ. One time in march 2015 I received a message from a friend while I was on holiday: “Martin! do you know the ‘Arktos Superspiel *(1)’? From Tabaluga TV? Do you think we can build this for the first semester student welcome?” I remembered an ‘ice-field’ represented by hexagonal, lit up plates where the children on the TV show were shown a ‘safe path’ step by step. Then, the markings disappeared and they had to walk across the field by remembering the path. Awesome idea, I thought and replied Well, it’s gonna take a lot of hard work and probably ~3000€ for the materials but yeah, sure we can!”.
After being back from my south-america-trip , we started brainstorming and prototyping. Thanks to many helping hands, we recreated this childhood-memory as a game with 60 fields for the first semester students and even won a price at the university.
The game is built as a set of 20 modules with 3 ‘ice-fields’ and an RF-module each; supplied by 10 computer-power-supply-modules. 2 transport-wagons were allowed us to store and transport the game and a software with a GUI allowed an easy, setup and automatic generation of the ‘path’ as well as measuring the missteps.
  • 14.940 LEDs (=249m of LED Strip with 60 RGB LEDs/m cut in pieces)
  • about 10.000 solder-points on 20 PCBs with 1484 holes drilled manually
  • more than 250m  of wire in 4.560 individual pieces
  • many square meters of 18-24mm thick, robust wood (60 hexagons, 360 frame-pieces with ~720 holes drilled
  • 20*2,4GHz Clients, 1 Masterbased on nrf24 and arduino nano like PCBs
  • roughly 4.000 (unpaid) man-hours invested by different students (thanks to an incredible amount of coffee)

=>  about 4.000 watt power-consumption and lots of fun!

It’s important to note that all of us worked without pay and spent many hours of our free time (even during the exam phase) to create an awesome experience for the first semester students. Thanks again to everyone who helped to realize this idea!

Some of the main issues we encountered:

  • LEDs emitt light at an angle of up to 130° but if the glass is palced too close to the LEDs, individual LEDs are visible. We tried different acrylic-glasses up to 8mm but girl’s heels or small stones in the profile of a shoe could still have broken the acrylic glass with 50-100kg being concentrated on 1 spot. For a homogenous light-effect, we would have needed at least 3cm between the LEDs and the ‘glass’-surface while being able to withstand high pressure. The only solution that might have offered these properties would have been translucent resin or at least 12mm acrylic glass mounted around the edge. Both are options that were out of our budget so we settled for thin, 3mm acrylic glass with ice-optics being placed on the silicone-film of the water-resistant LED-strips.
  • Pressure sensing was another task we had to solve. We tried load-cells, capacitive or optical measurement with spring-loaded inner-hexagon-plates, pushbuttons and piezo-electric force-sensors. In the end, the simpelest solution was the best: ESD-foam! The black foam used for packing electronics has a high electrical resistance (but is conductive). When the foam is compressed, many ‘bubbles’ form a short circuit and the resistance decreases by a huge factor ( 10kΩ to 5.5kΩ ) so we didn’t even need operational amplifiers . The foam also expands itself afterwards. For this, we placed a copper-strip on the bottom of the hexagon-frame and on the bottom of the LED-plate with a piece of 4mm thick foam inbetween.

Ps: To avoid any risk for the students / children that might play the game, we kept all self-built parts at the 12V-level and used standard PC-power-supplies to power the game.
(*1) The name ‘Arktos superspiel’ is most likely trademarked by Tabaluga TV but not know outside of the german speaking community. If you want to know more about the game, feel free to google the name and rewatch some old episodes on their channels/websites

Lighting up the living room

I’ve always loved LEDs sind I built my first 5mm-LED Flashlight in a ballpen-casing back in 1999. So LEDs were bound to become a part of my new appartment. For watching TV, partying or simply a nice, dimmable light I wanted to have indirect LED-lighting in my living room. Without wasting much space or money, I decided to mount it on the walls: A small cable-canal offeres a great solution to mount LED strips facing upwards and/or downwards while a black wooden cover-plane (~5cm tall) serves as ‘shade’ to avoid the glare of individual LEDs. Two RGBW-LED-controllers offer wifi connectivity and control via smartphone, tablet or Alexa (via the ‘Magic Home’ App). Here’s how the ~ 12m Warmwhite and ~12m RGB-Led-Strip look in my living room:
As you can see, they are bright enough to replace conventional lighting entirely.

Shopping-List ~ 130€:
– RGB-LED Strip, 60 [5050]-LEDs/m, 12m 24€
– WarmWhite LED-Strip, 60 LEDs/m, 12m 20€
– RGBW Wifi controller, *2 30€
– Power Supply, 60W *2 30€
– Cabel-Canal, 12m 8€
– Wooden 100cm*5cm*0.4cm-Panel * 14, 13€
– short screws, rawplugs, hot glue, black paint, 4m DC-cables & Tools