Redesign of Color Organ PCB: Pulsating to the Sound of Music

Redesign of Color Organ PCB

Abstract

The objective of this project was to create a PCB using an already existing schematic that was proven to work. For my project, I chose to modify the LED layout of a color organ into a more interesting shape. The through hole resistors and capacitors were also replaced with SMT components to allow for more space for the redesign. The redesign came out successful, except for a slight error on the PCB layout that was corrected by adding a wire. Other than that and some trouble soldering the SMT components, the project went smoothly.

Project Description

A color organ is typically an electromechanical device that represents analog sound as colored lights that correspond to certain ranges of sound (typically low, mid, and high ranges) (Fig. 1). Given how prevalent digital sound is in today’s society, it was only a matter of time until someone developed a digital color organ. This particular color organ uses only simple NPN transistors to separate the different voltages and currents produced by a headphone jack to their respective ranges. The sound ranges are represented by red, green, and blue LEDs that denote the low, mid, and high ranges respectively (Fig. 2)

Figure 1

Figure 1 - Frequency ranges for each LED; red less than 320 Hz, green between 320 and 2.4 kHz, and blue above 2.4 kHz.

Figure 2

Figure 2 - LEDs of the color organ lit up simultaneously to show the shape of the layout. The red, green, and blue LEDs represent the low, mid, and high ranges of sound respectively.

The original schematic had each channel (range) split into two rows of LEDs which led me to essentially wrap the LED rows for each channel around each other and other components in order to get my desired layout of a spiral star. An explanation of the board components and layout can be found in Figure 2. The components in the circuit essentially help the transistors direct the additional audio voltage to their respective “channels” of LEDs, either low, mid, or high.

Redesign of Color Organ PCB

Figure 3 - Finished PCB of the color organ redesign. All resistors (SMT) are underneath the board, along with some SMT capacitors. The black compoents at the QX locations are the NPN transistors which are the "directors" of the sound ranges wo their respective LEDs. The audio jack to the lower left provides additional voltage on top of the 12 VDC from the power jack (lower right). The component at VR1 is a potentiometer which allows for the sensitivty of the LEDs to be adjusted depending on the input audio. The blue wire in the lower right of the image is the correction wire that had to be added to make the circuit work properly and complete the ground for all the components.

The LED response to audio input is fast and accurate despite being restricted to three ranges. The potentiometer adjustment allows for fairly fine-tune adjustment of the LEDs to correct their response times and ranges depending on the strength and quality of the input audio.

Conclusion

Replacing the resistors and some capacitors from through-hole to SMT was easier than I expected, just matching up the values from the creator’s BOM was enough to reproduce the exact same results while allowing for greater design freedom of component layout. Soldering of SMT components was also much easier than I anticipated, although on some occasions the components burnt out from the soldering iron. Once the board was fully assembled for the first time and was plugged into the power and audio sources, it did not work at all. I adjusted the sensitivity knob of the potentiometer, but nothing made it work.

Determining what was wrong with the board was an intense process of trial and error. I started off by checking every solder joint on my board to ensure that all the connections were secure. After that, I measured the resistance values of the SMT resistors to make sure they did not get burnt out during soldering. I also check the power supply to make sure that the input to the board was correct. None of these attempts yielded any solutions to the board not functioning. I decided to turn my attention to the schematic and see if I made a mistake in designed the traces of the PCB.

This is where I realized my error, although I was lucky that the solution was a fairly easy one. As it turned out, I had mistakenly left out a ground trace to the negative lead of the power jack component. What I had done in my design was essentially cut of the ground from all the components and was trying to run it through a capacitor before it could reach the proper ground. All that had to be done to rectify the problem was solder a wire from the negative lead of the power jack to the junction of the grounds for the rest of components, before the capacitor that was stopping them all. Once this was done, I plugged it in and the board worked as planned. The ambiguity of the creator’s schematic caused me to misunderstand it when I was designing the PCB layout.

This trial and error process made me respect the designers of PCBs that go into consumer items, the time and effort that goes into designing the board, testing the board, and doing calculations to ensure the outputs are correct. Even one oversight, however small can completely prevent the board from functioning and I am sure that most issues that people run into regarding the design of PCBs are much more complex and harder to fix than my grounding issue.

I would highly suggest that you make sure that you fully understand the schematic and what it is trying to say. The schematic is the core and basis upon which you design the PCB so if you do not understand completely how all the components are connected, you will likely make the same mistake I did and not make all the necessary connections and will have to develop

Downloads

Related Content