Walls often make up more than half of indoor surface area, especially in residential and office buildings. In addition to delimiting spaces, both for functional and social purposes, they also hide infrastructure such as wiring and HVAC. However, they are generally inactive structural elements, offering no inherent interactive or computational abilities (other than at small attached silos, e.g., thermostats and light switches), and thus present an opportunity for augmentation, especially considering their ubiquity.
Researchers have transformed walls into smart walls at relatively low cost — about $20 per square meter — using simple tools and techniques such as a paint roller. These new capabilities might enable users to place or move light switches or other controls anywhere on a wall that’s most convenient, or to control video games by using gestures. By monitoring activity in the room, this system could adjust light levels when a TV is turned on, or alert a user in another location when a laundry machine turns off.
The process, materials, patterns, sensor hardware, and processing pipeline is called Wall++. Conductive paint is used to create electrodes across the surface of a wall, enabling it to act both as a touchpad to track users’ touch, and an electromagnetic sensor to detect and track electrical devices and appliances. A water-based paint containing nickel was chosen.
Using painter’s tape, a cross-hatched pattern was created on a wall to create a grid of diamonds (see figure), which testing showed was the most effective electrode pattern. After applying two coats of conductive paint with a roller, the tape was removed and the electrodes connected. The wall was finished with a top coat of standard latex paint to improve durability and hide the electrodes.
The electrode wall can operate in two modes — capacitive sensing and electromagnetic (EM) sensing. In capacitive sensing, the wall functions like any other capacitive touchpad: when a person touches the wall, the touch distorts the wall’s electrostatic field at that point. In EM sensing mode, the electrode can detect the distinctive electromagnetic signatures of electrical or electronic devices, enabling the system to identify the devices and their locations. Similarly, if a person is wearing a device that emits an EM signature, the system can track the location of that person.
The wall hasn’t been optimized for energy consumption, but the wall-sized electrodes consume about as much power as a standard touchscreen.