Step 1: The Vision
We quickly joined forces with the university radio station, Radio K, and asked many other technical student organizations to bring their creative elements to the show. We brought in a stage for performing student groups, and even brought in local businesses that provided free food for the opening night. It was a night of lights, music, food, and community. The show consisted of the Trans-Siberian Orchestra'sWizards in winter, and Also sprach Zarathustra, best know for its use as the opening theme in the film 2001: A Space Odyssey.
The show didn't stop there. We continued the next night, and the next again, for weeks on end. With media attention from local news stations, newspapers, and the university, people from around the Twin Cities continued to flock to this community event. Hundreds attended the shows, and we plan for an even bigger and more engaging spectacle in years to come!
Step 2: The Ornaments
We made seven stars, and hung them on a curved wall of the plaza. Each star was made out of five sticks of bamboo. A string of rope light was affixed around the perimeter with zip-ties. The stars were held in place with a combination of wooden stakes and twine.
Step 3: Snowflakes
Step 4: Trees
In addition to our bamboo and zip-tie trees, we also filled the branches of the plaza's real trees with lights. We also lined the flower beds and railings with rope lights.
Step 5: The Electronics
The requirements for each dimmer was simple: use a DMX signal to control sixteen strings of LEDs.
Although a modern switched mode power supply is much more efficient, we decided to stick with a simple linear power supply. The power supply has three main sections: an isolated RS-485 receiver supply, a microcontroller supply, and the LED driver supply.
The DMX input of the circuit board uses a separate supply voltage to power an RS-485 receiver chip, and is fully isolated through an optocoupler. The microcontroller has its own 3.3 V supply, but shares a common negative with the LED drivers.
We say "negative" and not "ground" because the LED drivers are powered directly by the unisoltated, rectified 115 V mains. The negative rail has an 80 V potential with respect to earth ground. This is definitely not the best design, but it eliminates the need for a bulky and expensive isolation transformer capable of powering all the lights. A bleeder resistor connected across the main capacitor safely drains any residual charge.
The RS-458 receiver chip converts the differential signal to UART, which is read by the microcontroller's serial port. We used a PIC18F24 to decode the DMX protocol. DMX is an industry standard protocol for controlling theatrical lights, making our circuit fully compatible with existing equipment. Five DIP switches allows us to select which of the 512 addresses in the DMX universe the lights will respond to.
From the microcontroller, two PCA9624 LED drivers are addressed over the I2C protocol. These drivers output a PWM signal for each of the 16 channels of lights. Each channel is amplified with a FET driver, and finally a large MOSFET. The resulting output can drive a string of LEDs, and is fully dimmable with eight bits of resolution.
To actually control our lights, we used a program called Q Light Controller, and a USB to DMX interface. Our lights were painstakingly sequenced to music, choreographing a visually stimulating show. This was one of the longest processes in the entire project, but in the end the show could be started with a single keystroke.
Step 6: Manufacturing
We chose to use mainly surface mount components, since through-hole designs are nearly obsolete these days. Most of our team members had never touched a soldering iron before, so our project took on a teaching phase. Fortunately a couple members were seasoned experts, and under their guidance, everyone was soon soldering away.
We built everything ourselves, right down to the DMX cables. We used a spool of outdoor rated CAT5 cable, and carefully soldered the requisite 5-pin XLR connectors on each end. While the connectors were expensive, we decided it was worth being able to reuse our electronics with any standard DMX setup.
Step 7: The Code
The program lacked some features we wanted, such as the ability to dynamically generate a light show from a song, so we have already begun developing our own program for next time.
Step 8: The Proposal
In case you're wondering, she said yes.
Step 9: The Group
By allowing individuals to propose their own projects and providing quality resources to make them successful, we encourage students to dream, design, organize and carry out every step in the process of discovery and invention. Because our members come from a broad range of technical backgrounds, each offers a unique contribution to the depth and quality of our projects.