There are 49 blue LEDs arranged in a 7x7 matrix on the QT2 Xplained Pro extension board that can be used to visualize a touch in the QTouch sensor. All LED's on the boards driven by the LED matrix driver (IS31FL3728), which is controlled by I2C. For detailed instruction how to interface the LED matrix driver, please refer to the devices datasheet at http://www.issi.com/.