LED array turned into touch button

December 29, 2004/January 5, 2005

A researcher from Carnegie Mellon University is using a grid of light-emitting diodes, which are widely used as light sources, as an input device.

The ability of light-emitting diodes to sense light is a well understood but little-used property. In fact, existing light-emitting diode displays can be made touch-sensitive without adding appreciably to the cost of the display, according to the researcher. In some cases a simple circuit change is needed, and in others only a software change.

The researcher's prototype acts as a touch button. Because it is also a display, it is also capable of showing prompts.

The advantages to using light-emitting diodes as switches are the ability to combine prompting with input and being able to do so in a sealed device that has no moving parts. Many existing appliances already sport light-emitting diode arrays. In these cases it is relatively easy and extremely inexpensive to add simple input and interactivity to the device, according to the researcher.

The researcher's technique requires at least two light-emitting diodes, one that senses light and one that emits light. When a translucent or reflective object like a finger makes contact, it reflects light from the emitting diode onto the sensing diode. The device can be configured as a button by triggering an action when the intensity of the sensed light passes a threshold corresponding to an object touching the device.

Input devices based on the touch sensing capabilities of light-emitting diodes can be used practically now, according to the researcher.

The work was presented at the User Interface Software and Technology 2004 conference (UIST '04) held in Santa Fe, October 24 to 27.

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