FROM EDN EUROPE: LEDs take over in "mood" lighting
By Graham Prophet, Editor -- EDN, June 8, 2006
Architects and lighting designers are enjoying new freedom in the creation of lighting effects with systems based on LEDs; using tricolour arrays of LEDs, they can fine-tune intensity, colour and pattern to achieve "mood" lighting. Designers need to ensure they apply the correct drive to the LEDs, and they need to program the desired patterns into LED arrays. Lighting specialists who have never dealt with such software and hardware issues need to begin working with a new technology; and circuit designers who have not previously worked with the architectural sector will find themselves working with new clients.
For both groups of designers, distribution company EBV has developed a reference design and demonstration board that mounts a 5×5 array of tri-colour LEDs on a pcb that acts as a "tile", allowing designers to build an effects lighting panel of any desired size. The pcb measures 76×76 mm and is populated with 25 Osram RGB LEDs. To drive each diode individually for full control of effects requires 75 PWM (pulse-width-modulated) channels, which EBV has implemented in an Altera MAX II EPM 1270 CPLD (complex programmable-logic device). The MAX II chip is suited to this application, according to EBV, because its I/O pins can sink up to 25 mA per pin and can therefore drive the LEDs directly. The logic on the CPLD implements the PWM channels, handles the communications and decodes incoming data into control signals for each LED. For demonstration purposes, the board integrates an RGB colour generator to show a rainbow effect running over the array. Two RS485 and one RS232 input channels allow you to feed external patterns to the pcb. EBV can also provide a graphic-effects controller board that its partner company ecue (www.ecue.tv) designed, together with software to create light effects and patterns of the designer's choice. The DBMAXLED board comes as a kit for €250.
