LED Display Lighting
Unidas flagship store located in Lima Peru, celebrated its grand opening early in 2006. The business specializes in perfume and cosmetics. The floor plan features a river of acrylic ice rocks located along the back wall. The ice rocks positioned just below a range of product displays will create an incredible effect as they reflect light produced from an LED controller and set of chasing LEDs positioned directly above. The overall length of the LED display lighting is approximately 70 feet. A small LED controller module located near one end of the chasing LED array provides the Unidas employees with a user-friendly interface to switch between modes of operation. Approximately two dozen pre-programmed sequences include various LED chase, fade, and strobe functions. The user also has the option to select a single continuous color mode, and produce unique LED lighting designs. Altogether, we decided to incorporate seven distinct colors by combining individual red, blue, and green LED circuits.
LED Display Lighting
The 70-foot chasing LED array is composed of 70 individual printed circuit boards electrically connected by a series of jumper wires. Each LED circuit board measures only 0.5 inch wide and contains six red, blue, and green P4 Super Flux LEDs (light emitting diodes). The P4 LED package features a relatively high luminous output and is fair in terms of cost efficiency. Although several high power LED lights surpass the P4 as far as cost efficiency and offer a higher luminous output, they also dissipate more heat when compared to the P4 package. A single 150-watt Lambda power supply, rated for 12.5 amps, powered the LED display lighting and LED controller circuitry. However, the entire LED array only drew approximately 5 amps, or 40% of the power supply's current rating.
LED Controller
The LED control module contains a PIC Microcontroller responsible for storing preprogrammed routines. The PIC10F220 is a microcontroller IC with amazingly small physical dimensions, commonly utilized in LED tail lights. Minimal external component requirements enabled a compact but effective LED controller design. A small external push button linked directly to the PIC allows the user to select between operational modes as desired. After depressing the button for 10 seconds, the custom LED lighting device switches into program-select mode. Each subsequent depression will advance the LED array to the next preprogrammed routine. The PIC automatically switches out of program-select mode after a short period without registering a user input. This is how the LED lighting device returns to standard or operational-mode.
Chasing LEDs
Undesirable voltage drops are the primary obstacle associated with a chasing LED array of this magnitude. The electrical connections between each LED circuit board can result in a voltage drop as high as 100 mV (0.1 volt) per connection. Considering a 12-volt power supply, the available voltage will decreased by 60 percent, to only 5 volts on last circuit board in the array. This was the initial problem associated with using a standard pin and socket type system on this specific project. To resolve this problem, one-inch stranded wire leads were soldering directly between each LED circuit board. Fortunately, this would not create a major obstacle during transportation due the stranded wire flexibility that allowed for folding of the entire LED array neatly into a single box. Although this could have been a major design issue, a more serious problem troubled engineers during initial design stages. The LED circuit board traces required to carry significant amounts of current would cause additional voltage drops as well as dissipate additional heat. Rather than increase the width dimension of each circuit board, an external power bus would supply current to three separate locations along the LED array. This would significantly reduce the load on circuit board traces without increasing overall costs otherwise induced by attempting to integrate a power bus directly onto the array of LED printed circuit boards.