pretty much work exactly the same except for how you init them, but if you use https://github.com/marcmerlin/FastLED_NeoMatrix_SmartMatrix_LEDMatrix_GFX_Demos/blob/master/neomatrix_config.h , you can just include that and your same code will work on both FastLED backed matrices and SmartMatrix backed matrices, even though they are totally different technologies.
RGBPanels do use less power even when corrected for amount of brightness generated (my estimate is at least 3 times less), they can be a lot more dense, they're cheaper, but they're a pain in the ass to drive since they require constant refreshes at high speed. That being said, as long as you don't exceed 128x64, which is more or less the practical limit on teensy 3.6 and ESP32 due to memory limits due to how SmartMatrix works (a different implementation could push things to at least 128x128 by sacrificing quality for memory use).
The demos I used for the pictures below are
After months and months of work, here is version 4:
Sadly, going up in resolution with addressable pixels, is not that easy. While in theory you should be able to fit at least 2 addressable pixels per centimeter (aka P5). Currently my premade panels are P10, which is the only thing I could buy pre-made.
What allowed me to switch were those flexible P4 RGB Panels from Azerone: https://amazon.com/gp/product/B07F87CM6Y
With their P4 resolution, I'm able to fit 96x64 on my body using 3 panels of 64x32 chained together. The 3rd panel is then chained to the 2nd set of 3 panels in my back:
On the old shirt, I put the rear panel inside the shirt, using the shirt as a diffuser, but with the RBGPanels, they were too thick for this to be practical, so I had to put them on top of the shirt. As a result, I ended up uing a black shirt which matches the color of the panels. I had to attach velcro to the new shirt, and confirmed that supergluing them was so much faster than sawing, and worked just as well:
I unsoldered the power connectors that were too thick, and used small metal wire to connect the panels together (see top middle of the picture). Turned out those metal wires were a mistake as they can cause shorts on the LEDs on the other side of the board:
Another thing I learned was that the holes I was using to put a metal wire to carry the panels over my shoulders, can't actually take the load, and the wire can cause damage to the copper trace that is just next to the hole. As a result, I replaced the metal wires with fishing wire and didn't use the bigger holes for load bearing:
Speaking of removing thickness from the board, I removed the top of the ribbon connectors to make them a bit thinner. Sadly, RGBPanels still require 15 wires to send the video signal:
I then took one panel and covered it with defusing foam (the rear panel, so that it's not too sharp and blinding to people behind me), while the front panel only has the plastic cover to protect the panels and offer a bit of extra diffusion:
you can see the difference between the diffusion levels
I then protected the rear of the panels given how much electronics were exposed:
Small details had to be solved, like making sure I had enough amps going through the wires (use thicker wires). Without that, my brightest pattern that uses 8 amps, didn't quite make it:
For fun, I made a pattern that scrolls my C++ scrolling code on the screens:
I went from a breadboard prototype to Jason Coon's ESP32 level shifter board, much more tidy
This video shows how things are wired from the ESP32 to the panels:
Here is what the whole power system looks like:
2 4S Lipos, 5Ah, 80wh, giving a total 160Wh of energy
Amp meter in line with the lipos and cell tester with low voltage warning buzzer
Amp gauge with timer to know how much energy flowed from the batteries (you can't run lipos down or they'll die)
Tobsun DC-DC converter to take voltage down to 5V
2nd voltage regulator to bring the voltage further down to 3.3V for the El Wire glasses
5V goes to RGBPanels via separate thick wire to carry the amps
ESP32 with level shifters from 3.3V back up to 5V for the RGBPanels (6 channels for the colors to level shifters, 4 address lines to do 16 scan line refreshes). CPU runs SmartMatrix::GFX and NeoMatrix-FastLED-IR
16th data line is used for the Neopixel strips on my arms and legs, running the same code than the previous shirt
Here is an example of 3 levels of diffusers, including a raw set of panels with no diffusers:
You can see a demo of the outfit being worn:
If you don't have time for all this, and are ok with 64x64, you can try this backpack from gearbest with everything built in and a very thin board. Just not fun for me because I can't run my own code on it:
RGBPanels are a totally different technology based on row scan technology, pretty much like the 8x8 matrices I wrote a scanning driver for but with a built in shift register to load up all the column for each color, multiplied by 2 as for historical reasons you can update 2 halves of the panel separately.
With 32x64 panels, or even 64x64 panels, that's a lot of pixels to push serially via shift registers and address lines to select the line you've currently pushed all those columns for. The LEDs need to be refreshed very quickly to avoid visible flickering.
This limits the list of reasonble CPUs for higher resolutions to teensy 3.6 and ESP32, which also removes the multiple slower and/of inefficient drivers out there. Options I looked at and weren't suitable:
Best support for chaining panels (up to 128x128 on teensy, and maybe 64x128 on ESP32 before it runs out of DMA RAM)
High color depth 24bpp or higher (which honestly is more than I need, 24bpp is more than most panels can probably reasonably show and 16bpp would likely be enough for my use). I still wouldn't mind if SmartMatrix offered 16bpp in exchange for a higher refresh rate or lower resource and memory utilization (also allowing for a higher resolution on a given CPU)
Support for the 2 fastest common arduino like microcontrollers: teensy 3.6 and ESP32 (teensy 3.1/3.2 is not fast enough to refresh 64x64 well enough, and teensy 3.5 is slower than 3.6, so no reason to buy one)
Very powerful API with multiple layer support (great if you can use it, although I'll admit that I only need drawpixel thanks to Adafruit::GFX)
So, SmartMatrix is great, but I have all this code that relies on one or more of those APIs:
The easiest way to use SmartMatrix is to use the SmartMatrix Shield v4 from Louis Beaudoin.
If you are going to drive 64x64 and above, skip the teensy 3.0/3.1/3.2 and go directly to teensy 3.6. It costs more, but you'll want the extra CPU speed (teensy 3.1 can barely run 64x64 with an ok-ish refresh if you overclock it, if you must use the older chip).
Here is what the SmartMatrix shield looks like with a small patch I made to take USB power and send it to the panel (my laptop can output 2A over USB). Note that this is not safe with teensy v3.1/3.2 as it's not meant to pass that much current from its USB connection, but teensy 3.6 can do it fine as its fuse is located after the V+ connection on the chip:
Originally I used the APA connector to send power to the panel
2x 32x64 chained P4 panels with a sad cable extension I had to make, vs pre-made 64x64 P3 panel
SmartMatrix basic demo
The main problem with RGBPanels is that if the refresh rate isn't fast enough, they look bad on pictures. This is the main reason I switched to ESP32 which is dual core and can push a higher refresh rate via DMA than teensy can:
Chained panels giving mirrored output on a total display of 128x96:
As mentioned above, ESP32 is dual core, so it can update the panel on one core using DMA, while the other core can run your code. It is more efficient, however, it runs out of DMA memory around 64x128 resolution (I run 64x96 myself and had to optimize code to make things fit)..
Here are shots of what it looks like with Jason's shield:
it's reasonably compact, 15 IO's for SmartMatrix (14 are really required), IR connected to port 34, and IO 16 connected to a NeoPixel strip
This shows my flexible P4 96x64 panels I bought on amazon from Azerone, 3 tied together, one shown upside down for scale, a blank shield from Jason Coon, how I cut a 16 pin IDC ribbon cable and made it an in line row of pins I can connect into Jason's shield after having added a riser, and a patched board with IR connector on the back, and a yellow wire to redirect the pin Jason's board connected to RX which I use for debugging, to unused pin 27 instead:
While Jason's board is not perfect for this use, it's much better than my self made protoboard full of wires to connect the 74hc245 level shifters:
Here's a quick video summary that shoes the wiring and layout: