For our project, "Take a Seat," a public space installation for Munich Creative Business Week, we transformed a 23-meter-long picnic table into a social hub, inviting people to interact.
While the installation welcomes passersby, we wanted some magic to happen in the details: Rather than illuminating the entire space, the table lights should turn on only when two people sit down opposite each other, ready to share a moment. We imagined little islands of interaction.
In order to maintain the warm and welcoming nature of our installation we wanted the technical solution to be visually imperceptible and minimize wiring. Here is how we made it possible:
Our first idea was to use ultrasonic sensors mounted below the table surface that would switch the lights on by detecting the reflection of the waves by the bodies of the people sitting on the two opposite benches.
We quickly hacked some prototypes and went directly into real-life testing. While the solution worked in most circumstances, we still were not fully convinced: reflections caused by arbitrary objects near the tables could lead to lights randomly switching on. At the same time, if someone sat down on one of the outer sides of the bench, the sensors would probably not detect the reflection. Both problems would lead to an unreliable operation of the lighting and therefore we had to find another solution.
For our next iteration we chose two ToF sensors per table, one per seat, that would be controlled by an Arduino Nano.
"ToF" stands for "time of flight." The sensor emits infrared light pulses and calculates the return time of the reflection.
In order to measure the maximum distance between the table legs, we placed sensors at knee height. If an obstacle is detected between the two legs, it means someone is seated.
However, we had to solve a problem related to the length being monitored. The table seats were 2.2 meters long, but our sensors only covered up to 1.8 meters. Beyond that distance, incorrect measurements could occur, causing people to be missed.
We solved this problem by using reflectors positioned on opposite sides of the sensors. The reflectors amplify the reflected light, which stabilizes the measurements obtained by the sensors at 2.2 meters. Any reduction in this measurement means "seated person".
Finally, each Arduino controls a 24V light.
The lights and Arduinos are connected to a 312W power supply, which is located in the box under the first table.
From prototype to product: the PCB board.
During the period when the installation was running, we observed people continuously filling up and emptying the table. Groups formed spontaneously, with strangers sharing the same space for a few minutes. Everything was working as intended.
All of the technical complexity described here serves only one purpose: to make interaction feel natural.
If people sit down, the light comes on. If no one is there, it stays off.
The electronics, software and sensors simply facilitate this process.
