Integrating Touch User Interfaces with LED Lighting

Touch based user interfaces controls have become common for controlling consumer electronic, commercial, and industrial systems. Most recently, the architectural marketplace has been quick to incorporate touch controls with LED technology.  At the May 2012 Lightfair convention in Las Vegas, dozens of touch based light control systems were showcased.  In fact, the Illumination Engineering Society (IES) has an excellent overview topology (publication TM-23-11) on the structure of an LED control system that could feature a touch based interface.

Reprinted with permission from Lighting Control Protocols (TM-23-11) by the Illuminating Engineering Society of North America.

For this discussion, we’ll focus on the “front-end” of the diagram. The most common way to detect a touch is by indirectly sensing the conductive mass of the human finger. Sometimes referred to as “capacitive” touch, this technology relies on detecting an electric field disruption of an approaching finger with a sensing electrode below a dielectric decorative substrate like glass or plastic.  Successful specification, design, and implementation of a touch-based user interface require a basic understanding of the active elements that comprise the system.

The dielectric decorative substrate is best described as the surface that a user touches when interacting with the interface. Typically constructed of glass or plastic, it serves as the primary aesthetic element in the product’s user interface design. In the case of touchscreens, the decorative substrate is usually planer and constructed of glass. In the case of discrete touch points, the geometry is almost unlimited with touch points integrated into many surfaces (commonly injection molded decorated plastic). The decorative substrate can also be backlit for aesthetic or functional purposes.

The electronic carrier is the element containing the sensing electrode structure and interconnects for the touch user interface. Discrete touch points (fixed touch points behind decorative icons) frequently use rigid FR4 printed circuit boards and touch screen use transparent conductive electrodes. Electronic carriers can be in the form of an external circuit or integrated with the LED driver. When designing touch solutions, thinner is better. A thinner decorative substrate and a thinner electronic carrier result in better signal to noise ratios resulting in a more robust touch solution.

LED drivers that are microprocessor based become excellent candidates for an integrated touch control, particularly if the driver circuit is co-located with the user interface. Since many microprocessors can be configured as touch controllers, cost is reduced with a simple solution. Several manufacturers offer low-power touch controllers that are suitable for battery operated “touch” remote controls which can connect to the LED driver using a wireless protocol such as ZigBee.

Norlux has extensive experience in the design of LED Drivers and has developed touch controls for the Architectural market. From simple on-off switching to full wireless intensity, color, and saturation control, Norlux is your one-stop partner for LED lighting and control solutions.

References
IES (Illumination Engineering Society) publication TM-23-11 (http://www.ies.org/PDF/Store/TM-23-11_FINAL.pdf)