p2:2 – 3D printed RGB LED sign – design

In the previous post, I laid out the plan for this project. In this post, I’m going to talk about the design I came up with. Thinking about this project, I wanted to try to minimize the amount of material used (always a good thing), the amount of power necessary, and the size, which of course is related to the other two elements.

design

dimensions

The first thing to think about is how big I wanted this sign to be. I didn’t want something that would take up a ton of space on the wall or be too big to fit on a shelf or side table. After playing around with my tape measure, I settled on a height of about 5 inches for the tallest letters. I was ok with however wide the font made the sign. With these dimensions, the sign would occupy about about 17 square inches. Large enough to be noticed but small enough to fit on a shelf or table. Perfect.

the look

As far as how it will look, I wanted the letters to be separated like they appear in the logo. But having them separated like that would make it impossible to hide all the wiring connections between the letters without mounting them onto some kind of back plate. A back plate was out of the question because I wanted it to look like just the words hanging on the wall. It would also not look as nice sitting on a table or shelf. I decided the solution would be to create an outline around each of the letters. The outline would allow me to connect the letters to each other to route the wiring and create space to house the other components.

battery, controller, switch locations

The next few points were a bit trickier. How would the LEDs flow and where will I locate the battery and controller? I decided the best part of the sign to house everything would be in the “all”. In my mind, the “l” is large enough to house everything. Of course, I don’t haven’t looked into potential battery sizes yet, so this may have to change. The location, however, is easily reachable to allow for recharging of the battery and updating the microcontroller.

LED flow

With the words stacked as they are and the font being anything but blocky, I decided the easiest to separate the LEDs into three strips, each with its own power connection to the battery and each with its own data pin on the ESP32. Based on my research, the FastLED library I will be using to write the program allows me to control all three strips at once and even combine them to create animations. Therefore, the flow of the LEDs is pretty simple and will start from the bottom left and snake its way to the end of the word on the bottom right. I would draw this up but I am particularly poor at sketching up these types of drawings without making it look pretty ugly. Exhibit A below.

circuit design

As noted above, the battery power will be split four ways with three going to each LED strip in each word and the last one going to the ESP32 microcontroller. I initially thought I would add a switch to power off the sign when not in use, but I learned that I can put the ESP32 into a sleep mode. In addition to turning off the LEDs, the sleeping ESP32 should draw minimal power from the battery.

There is a capacitor in the picture below but I forgot to draw the resistors which would sit between each LED strip and the ESP32. As pictured, each strip will receive its data input from a different pin and will be controlled independently to create a cohesive animation and lighting effect.

Although the ESP32 (specifically the ESP32-WROOM-32 that I have) has a specification of 3.2v power input, it does accept a 5V power through the USB or through the VIN pin. When getting 5V, it will output 5V. Although this is irrelevant for this project because the LEDs are being powered by the battery, it’s good to know for the future. Utilizing this knowledge, however, I was able to test the LED strips using the 5V USB connection from my PC. CAUTION: There is a ground pin on the VIN side that should be used when using a 5V power source. Using the ground pin on the 3V pin side may cause damage! Be careful!

hanging/freestanding requirements

The sign should be light enough to hang from two screw hooks designed into the back of the “mike”. A simple template should make hanging it a breeze. As far as free standing, I want the lettering to have enough structure that it will stand vertically on whatever surface it sits on. I may have to design some sort of “feet” that blend into the lettering when hung on the wall, but give enough structure for the sign to stand on when on a shelf or table.

making progress

The next post will be about the modeling process in Fusion 360. I’ll undoubtedly have at least a few iterations and I’ll try to talk about what I changed and why. Stay tuned for more!

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