[help] LED matrix demonstration for climate change

Thread Starter

electroniczzz

Joined May 21, 2021
3
Hello!

I'm a junior undergraduate pursuing a degree in electrical engineering and I have a project idea I've been doing some research on. I have some experience in mBED microcontroller programming and design (like PWM and serial connections). I also have some experience in PCB design and circuit design and soldering.

Here is my project idea:

I want to assemble a grid of LED matrices (to form a display) fitted inside of a victorian era painting frame. The display will show the Mona Lisa and for every increase in daily carbon emissions levels (with data gathered from a government database), water will slowly flood the painting. Once the water level reaches the top of the painting (meaning the allowable carbon emissions threshold for that day has been surpassed), a glitch effect will be displayed on the display and the carbon tracking animation will start over. This is a rough idea of what it will look like. Note that the resolution is adjusted for the actual resolution of my LED matrix display. The purpose of the piece is to bring light to how incredibly fast we are exceeding the allowable carbon emissions level. The Mona Lisa flooding is supposed to symbolize the flooding of the Seine river in Paris, home of the Mona Lisa, due to climate change.

I want the quality and rugged electrical aesthetic to resemble this post, except instead of it being 1 led matrix, it will be a 4x3 grid of 32x32, 7.62 mm pitched indoor led matrices. I've arrived at this pitch level because I want to be able to make out the pixels (like in the referenced post), instead of mimicking, say, an advertising display. The creator of the referenced post uses a 3 mm pitched matrix, but since mine will be much bigger, I think P7.62 might be ideal. The total size of my display should be .732 m x .975 m, or 2.4' x 3.2'.

I’ve seen in multiple forum posts that Arduinos have very limited capacity to run LED matrices of large sizes (for reasons that I don’t quite understand) and that Raspberry Pi is definitely the way to go for small to mid-sized builds.

My first question is, will a raspberry pi be able to handle controlling a 96 x 128 resolution display, or do I need a video processor? I would say my project is somewhat in between a commercial build and a small consumer build but the two different techniques for each seem to differ significantly. Youtube videos of advertising screen assembly, as well as the informational documents on AliExpress listings, seem to be using large video processors, while this get hub tutorial suggests that you can use a raspberry pi. If so, would any particular Pi be better for this job? Obviously, I don't want to spend more than necessary, but I want a Pi that will have no problem handling the job. Does anyone have any suggestions?

Also, I've seen a lot of builds use those Adafruit Pi hats for connecting matrices to a Pi, but I'm sure that my external parts will not be compatible with their components. Does anyone know how to go about connecting the grid of matrices to a Pi when using non-Adafruit matrices?

My second question is, how would I determine the necessary power supply for the display? The other Reddit poster uses a 5V 6A DC power supply for his single 64 x 32 panel, but I'm curious about how he arrived at this amp rating. In the listing for the panel they referenced, the max power consumption is rated as 1000W/m^2. Since he only uses one panel, which is 0.0184 m^2, the maximum required power should be 0.0184*1000 = 18.432 W, right? If so, why don't they use a 3 A (calculated from 18.432 W/ 5 V = 3.7 A ~ 3 A) power supply instead of a 6 A power supply? Wouldn't 6 A fry the LEDs? (Sorry if my questions are dumb, I don't have much experience in externally powering electronics).

If my build will be 0.7135 m^2, and the max power rating is 500 W/m^2, shouldn't that mean I should use a ((0.7135 m^2)(500 W/m^2))/5 V = 71 A source? That seems like a ridiculous amount of amps. Does anyone have any insight on this?

Third, I’ve noticed that many of the builds online that are designed to show a full-color picture are somewhat overwhelming to look at, while the simple designs seem to look better (at least on camera). Is there any way to mitigate the harshness of the panels when the display is to be used at a close range?

Lastly, does anyone have any tips/suggestions for this project? I'm relatively new at DIY builds so any amount of guidance truly means the world.

Thanks for reading!
 

dl324

Joined Mar 30, 2015
12,929
Welcome to AAC!
If my build will be 0.7135 m^2, and the max power rating is 500 W/m^2, shouldn't that mean I should use a ((0.7135 m^2)(500 W/m^2))/5 V = 71 A source? That seems like a ridiculous amount of amps. Does anyone have any insight on this?
For large displays, you'd multiplex the LEDs, so power and the amount of hardware required won't be an issue.

Can't give any detailed suggestions without knowing more about how your LEDs will be arranged and how you intend to control them. Schematics and/or block diagrams preferred over verbal descriptions.
 

Thread Starter

electroniczzz

Joined May 21, 2021
3
Welcome to AAC!

For large displays, you'd multiplex the LEDs, so power and the amount of hardware required won't be an issue.

Can't give any detailed suggestions without knowing more about how your LEDs will be arranged and how you intend to control them. Schematics and/or block diagrams preferred over verbal descriptions.
Thanks for the reply!

Oh wow, I didn't even think about that. This would mean that I could potentially drive the entire grid of matrices with the current needed to illuminate one column of diodes, right? So I could theoretically power the entire thing with like 6 amps? Would this have an effect on the brightness? Since my LED resolution would be 96 x 128, I could only have one row of 128 LEDs on at a time, right? Wouldnt this have a profound impact on the maximum brightness. Is it possible to split up the rows into smaller groups so each LED can have more time to shine?

Best,
Jacob
 

dl324

Joined Mar 30, 2015
12,929
Since my LED resolution would be 96 x 128, I could only have one row of 128 LEDs on at a time, right?
You could have only 1 LED on at a time if you choose.
Wouldnt this have a profound impact on the maximum brightness.
When you multiplex LEDs, you increase the peak current above the maximum continuous current. The maximum allowed current depends on the LED and the duty cycle. Some LEDs that have a maximum continuous current of 20mA can be pulsed at 1A.
Is it possible to split up the rows into smaller groups so each LED can have more time to shine?
There are numerous timing options. You can also use high brightness LEDs to give you even more flexibility.
 
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