The light curtain



The light curtain has been designed as part of a smart home environment. It has one sensor that acts as an on-off switch and a capacitive slider that can be used to control the intensity of the lighths. The curtain is connected to an open source smart home platform through an ethernet connection. This means that the sensor and switch can also be used to control other devices in the home, or that the light on the curtain can be set due to the weather conditions or the mood of the inhabitants.


What have you made?

We have made an interactive light curtain with two sensors – one to sense if it is drawn open or close, and another one that acts as a capacitive slider. The curtain is part of a smart home environment. It thus can react not only to its own sensor inputs, but also be remotely controlled by the smart home systems that it is connected to. The sensor and slider are made from conductive textiles so that they blend in with the overall textile design of the curtain. Especially the slider is interesting, because it is embroidered from conductive thread and divided into three parts. Other parts such as the LEDs are conventional electronic components, mostly out of practical considerations – but we wanted to make as many of the electronic parts from textile materials such as conductive fabric and thread.

What gave you the initial inspiration?

The curtain has been designed as part of a research project. This means that we were collaborating with other research partners, mainly engineers and computer scientists, but also psychologists that were interested in how people respond to different interaction modalities. The idea of an interactive curtain emerged because we were looking for an artifact that would demonstrate the value of a smart home in a more pleasant and tangible way than with a conventional light source or a collection of hidden sensors that would track the inhabitants’ behaviour. We were also dealing with very different application contexts – one being in an interactive store, the other in a private home. We could make the curtain fit well for both scenarios: In the store, the curtain hangs in front of the changing room and displays if the room is occupied. In the home, the curtain hangs in front of the window, like a proper curtain should.
Curtains are also relatively simple and ubiquitous objects and thus leave ample room for ideas when it comes to interacting with them – drawing them open and close just being one possibility.

What is the original idea behind this project?

The idea of a curtain that serves as a light source is not entirely new, this has been done before. However we like the way that our curtain can be an interactive light source that communicates with other smart home devices and reacts to the presence of the inhabitants. The lights on the curtain thus can be set similar to the lights on the ceiling. At the same time, they can give subtle feedback to notify the inhabitants about certain events.
We were also interested in playing with how people interact with curtains, and the way that we handle the hanging fabric, since the research topic of our group is interaction with electronic textiles. The capacitive slider is a nice example of how electronic textile interfaces work and look differently than conventional electronic interfaces: They can be easily scaled up and are often made from textile production techniques, in our case embroidery with the sewing machine.

How does it work?

At the heart of the curtain, there is an Arduino Lilypad to control the lights and interpret the input from the sensors. Our research partners produced a custom-made connector for the Lilypad’s six-pin header so that they could directly plug in an ethernet cable and connect it to another Arduino with an Ethernet shield. This second board manages the communication to the smart home platform.
There are quite a few LEDs on the curtain, so we used transistors acting as a digital switches to dim them and turn them on and off. The LEDs are organized in six lines that can be set individually or together. A 5V power supply powers the LEDs and microcontrollers.
The on-off switch is a simple two-part contact switch with conductive fabric and magnets. If the curtain is drawn close, the fabric falls in pleads and the contact surfaces touch. The magnets make the connection sturdier – otherwise the signal from the switch would be very shaky. Once the curtain is drawn open, the pleads open as well and the switch is activated.
The capacitive slider is an embroidered pattern of three intersecting antennas, each shaped roughly as a diamond. With this form, we could read the intensitive of the capacitive signal when a person moves her hand back and forth over the antennas. Due to the length of the electrical connections, the capacitive reading is a bit tricky, so there is an ATTiny installed near the antenna to make the readings more robust. The ATTiny communicates the readings to the Lilypad via a one-wire protocol, which is less sensible to disturbance than the capacitive antenna itself.

How long did it take to make it real?

Being part of a research project, this is hard to quantify because we were developing the curtain in three iterations over several months. The time that it took to build and program the final model might be as much as four to six weeks, involving the expertise of different people such as a textile designer who made the circuit, an engineer who developed the Arduino protocol and code, and the computer scientist who connected the curtain to the smart home system.

How did you build it?

The curtain consists of two layers of material: One layer of heavy fabric that carries the connections and components, and a semi-transparent layer that hangs in front of the LEDs to diffuse the light. We had the curtain produced first and then added the electronics to it afterwards.
Experience taught us that with electronic textiles, one needs a full scale model to test the performance of the sensors and actuators. This was particularly necessary for this model because of the capacitive slider. Before we built the final curtain, we therefore made a prototype for the slider with the calculated length of yarn, the Lilypad and the ATTiny, debugged and calibrated it. This was one of the most difficult parts of the project.
In the final model, we used both sides of the fabric to distribute the electrical connections and to protect them against shortcuts – the VCC lines run on one side, the GND lines on the other. All the connections are sewn with a copper bobbin thread in a sewing machine. To do this, we needed a full-scale paper plot for all the lines, transfer the lines to the fabric of the curtain, and then sew in the lines by hand. All components that are not made from conductive texiles, such as the LEDs, the microcontrolles and transistors, are sewn on to the conductive traces, and the ends are carefully sealed with a bit of nailpolish.