Jarred Glickstein

Engineer, Designer, and Hobbyist

Realtime LED Lightshow: Experimenting with Spectrum Visualization

In essence this project is a spectrum visualizer, in practice it is equal parts awesome, education, and fun. The realtime LED lightshow is one part of the audio-visual entertainment system I designed and built for my bedroom at home. Audio signals from either a television or stereo are fed into the system, turned into a frequency spectrum, and used to display patterns on a strip of 900 individually addressable LED lights which circle the ceiling. The audio signal is also output to a set of speakers to complete the entertainment system using one of my Hi-Fi stereo builds. You can read more about that here. This project has evolved quite a bit since its inception, so this page is broken down as follows:

  1. System Overview
  2. Audio Input Sampling
  3. Frequency Transform (FFT)
  4. LED Strip Mounting and Communication
  5. Controls Enclosures and Power Supplies
  6. Remarks

System Overview

Audio Input Sampling

Frequency Transform (FFT)

LED Strip Mounting and Communication

Controls Enclosures and Power Supplies

I wanted a polished product for the power supply enclosures, and here they are. Both units house a 5V 200W power supply. The larger one at left also includes a generously sized shelf to house the digital logic controls in the future. For now, the USB-UART IC and logic level shifter are on a breadboard pictured in front of the power supply box, and all signal processing is performed by a desktop computer. In the future I intend to switch to an FPGA for signal processing and use a dedicated PCB for the audio input ADC and FPGA outputs to the LED strip. That system will then be fit in the space in the power supply box.

Each LED can draw a maximum of 20 mA per color, 60 mA per LED. For 900 RGB LEDs, this is up to 54 A on the power rails for 5 V light strips. Several tricks are implemented to make this possible. First, the light strip is divided into two halves, each half requiring only up to 27 A on the power rails. A current of 27 A would require 14 gauge wire, which is tough to work with. Instead, two 18 gauge wires are connected in parallel to provide power and ground in a total of 4 wires. The maximum current rating for this configuration would be 32 A DC, allowing continuous full-power operation of the LED light strip.

At the maximum current draw the LED strip would use 135 W (neglecting cable loss). Two 5 V, 200 W power supplies were selected to ensure the power supplies will remain unstrained during operation. One of the power supplies is shown at left, a cheap switch mode power supply commonly available online. When using this type of power supply, it's always a good idea not to attempt operation at or near the maximum rated output.


For a clean connection to the light strips from the power supply boxes, each box has a spade terminal block on the back. I pulled the power and ground outputs from the power supply out to one side of the terminal blocks, leaving the other side to connect the light strips. On the small box at left, you can see two positive and two negative connections going out to the light strip. A set of power and ground wires are run from each side of the light strip back to the power supply, to reduce the effects of voltage drop across the wire and reduce the current supplied through each wire.


Inside the box the power connection from the wall is wired to the power supply unit through an illuminated switch. The second switch on the box is to toggle illumination of the main power switch. The illuminated switch is great for debugging but I turn it off when the system is in use to keep the room dark for maximum enjoyment of the light show.


For a clean connection to the light strips from the power supply boxes, each box has a spade terminal block on the back. I pulled the power and ground outputs from the power supply out to one side of the terminal blocks, leaving the other side to connect the light strips. On the small box at left, you can see two positive and two negative connections going out to the light strip. A set of power and ground wires are run from each side of the light strip back to the power supply, to reduce the effects of voltage drop across the wire and reduce the current supplied through each wire.


Remarks

Knowing what I know now, I would switch to 12 V LED strips in future work. These strips implement 5 V regulators periodically across the LED strip to deliver 5 V. As a result, delivering the full 270 W to the LED strip would require only 22.5 A, less than half of what I had to design for in this project. Granted, I now know I don't come close to maximum operating conditions when I use the light strip, I still like to design for continuous use at the maximum output capability in case I should want to in the future, and in case any code accidentally drives the strip at full power.

I would like to diffuse the light into a more continuous display. The IP67 waterproofing in the form of a silicone sheath provides some diffusion, and I definitely would not remove the strip from the sheath to install it easier on the ceiling. It could still be better and blend each LED into a continuous visualization experience.

(C) 2009 - 2020 Jarred Glickstein. All rights reserved.

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