I happen to have a CanaKit Raspberry Pi 3 B+ laying around. Here's my attempts at making this work with FreeBSD 12.

BTW: Be sure to buy a "tester". You cannot test the lights easily as they need a very specific control signal to even turn on, so you'll need to have a known-good. I got an Alitove SP105E for $18 (probably from Amazon). It's controlled by a free download smartphone app via bluetooth. (See video below of this things default pattern.)

Note that this page is shown in archeological order, namely newest first. If you want to understand the events in order, start at the bottom.

The mesh is a piece of plastic deer fencing, 8' high, with roughly 2" squares. Roughly at each junction, a bulb is tied with a vineyard tie (just like the tie on a loaf of bread).

The pink square at the top left is a yoga mat I use to keep from destroying my knees on the cold concrete.

I've got my matrix set up in my workshop, and have aimed a webcam at it so I can test it from the comfort of my warm office area as opposed to perched on a stool in a cold shop working on a really old really slow computer!

I've added some new items to the test/idle loop. Some of them are interesting enough to need explanation, so see external doc idle loop/test explanations.

I really, really hate Python, but have still been unable to find a neopixel library for perl, so am looking at more recognized solutions. Currently investigating Falcon Player (FPP).

This thing is extensive, and appears to be massively powerful - outright amazing! I'll start a new page here for the FPP version of the project.

cpan install XML:LibXML
cpan install HiPi - nope, still blows chunks
HiPi perl modules for RPi (hipi.znix.com)
I followed the initial 64 bit directions, got a bad arcitecture error. Tried 32 bit, this seemed to complete. Still didn't get hipi installed though. Tried the cpan install directions, that has gotten it to install, yay!
apt-get update
apt-get install libmodule-build-perl \
libdevice-serialport-perl \
libfile-copy-recursive-perl \
libfile-slurp-perl \
libjson-perl \
libtry-tiny-perl \
libuniversal-require-perl \
libio-epoll-perl \
libimage-imlib2-perl \
libbit-vector-perl \
libxml-libxml-perl \
libwww-perl \
libperl-dev
cpan -i HiPi
Now when I try running my test program which does not call out I2C, it simply tries to initialize and do a test neopixel pattern, I get an error "i2c_write failed with return value -1 at /usr/local/lib/arm-linux-gnueabihf/perl/5.32.1/HiPi/Interface/Seesaw.pm line 263."
At least we're getting into the test program instead of barfing with HiPi not loaded.

The cpan install barfs with a bunch of test failures. Looking at the output, I think the tests are actually trying to control the board, and read i/o from it, and interpret the results. Perhaps my configuration is confusing it? Anyways, I'll just do a forced install without the tests and see what happens.
find / -name WipringPi -print
cd /root/.cpan/build/
ls -l
Decide which to use, I'm going with the highest numbered.
cd RPi-WiringPi-2.3633-5
make install
My program is now able to run, we're getting past the no such libary problem. Next is to see if it actually controls the GPIO... Yes, doing a new WiringPi, and a new Pin, he pin cntrol works, yay!

Now trying to get adafruit-neopixel operational. Getting nowhere. Trying HiPi::seesaw...
apt-get install -y libimage-imlib2-perl
cpan install XML::LibXML nope, blows chunks needing XML::LibXML
cpan install Alien::LibXML never mind, this hangs on xmlsoft.org

I built a new system on a new SD card (preloaded with noobs, and let it do all it's updates), on a new RPi 4B+ (from Raspberry Pi themselves). I then copied the python program I'd written on the old RPi that had gotten clobbered (see 20211227 below). Of course I always backed up the program itself onto an external server, so even if the SD card had died I wouldn't be screwed! I tried running the old program, and got No module named board error.
pip3 install adafruit-circuitpython-nepixel
All is working now, yay!

During the last few days of Dec and first few days of Jan, we had about a foot of snow, and freezing for over a week. This was followed by torrential rainfall, about 6 inches in 24 hours. The sockitbox was not able to handle these conditions. A day or so later, as the rains eased up, the grid stop working, simply no lights. When I opened it up, there was about an inch of water in the bottom of the box. The box was still closed properly so should not have leaked.

I had not seen any significant buildup in previous checks each week or so, so I believe this must be mostly a result of the snow melting as opposed to the heavy rainfall, as we've had significant rain before without this issue. The power supply survived, the wiring is all Ok, the RaspPi did not survive, it's simply dead.

You'll see from the setup photo below, that the Sockit box was simply sitting on a small tabletop, fully exposed to the elements - at one point there was almost a foot of snow on it. A side note, I did observe that there was the same amount of snow on it as on the balcony railing, which means it was not generating significant warmth - this means my power supply is reasonably sized, I'm not holding in excess heat.

Next year I will do something to protect the sockit box, perhaps simply stuff it in a plastic garbage bag, or maybe set it under the table, or place a piece of plywood on top. Here's a video of the final test pattern. It starts with the full alpha/numeric test with scroll, then "Perennial Vintners", and a candy cane red/white stripe. Same as previous plus video some test patterns in other vids below, including horizontal blank and snowstorm. Here's a video of the Alitove SP105E pattern - video made on a cold, rainy, windy night on my cellphone - please forgive.

Oh, and if I was to do it again, I'd go with the 12V instead of the 5V - perhaps there would be less trouble with the dimming strings further down the line that way.

I've simply strung the light strings along a set of horizontal wires to build a grid. Be sure that each row has the same number of bulbs. You will "lose" a few bulbs in the gap between rows (assuming like mine they are a more than one bulb distance apart).

The difficult part is that the length of wire between "bulbs" is very inconsistent, so you cannot get a clean grid this way - which makes lettering too ragged to read. The fix will be strictly mechanical, but right now I've been concentrating on the other facets of the project.

I used a "sockitbox", size "medium" to hold the guts. It's a normal old Raspberry Pi. I originally built it with a CanaKit 3B+, but in the process I managed to kill the UART signal output, so had to replace it, this time with a 4 from Raspberry Pi themselves.

What they don't tell you, is that although these LED strings can connect together in a long line, they won't be able to run that way. I don't know why this happens, the wire between the bulbs appears to be of sufficient gauge to have a long string, but evidently it's not, as the bulbs will be noticably dimmer into the 3rd string, and outright dead by string 4 or so.

My original setup was a plastic power block with Alitove branding (like you have for a laptop) rated at 5V 75W. This was not sufficient. I got two more, which filled up the Sockitbox, and wired them in at each 3 strings - still not sufficient. Bottom line is that each string, at full bright and white, seems to take about 50W. I dumped the block supplies into a box in the garage with a sigh while lamenting $100 wasted, and ordered a MeanWell UHP-500-5 power supply which seems to be perfect (in photo). The 3 blocks together could manage 225W, this one is rated at 400W, takes less space, and costs about the same.

Note that buried under the blue tape is simply a 40 pin connector, plugged into the RPi board, with a ground wire and GPIO 18 (physical pin 12), passed through to the 3 pin connector for the LED string.

One thing I have noticed is that one of my test patterns, which was cribbed from a neopixel demo, is supposed to have a rainbow background. This DOES work when I have a single string on my dining room table, but is a solid green background when outdoors on the "screen". I did not spend additional effort on this yet, so not sure what needs to be done here. I'm guessing adding a transistor to drive the signal line instead of relying on the meek rPi output directly might be the fix.

At each 3 strings, I've had to add a junction in for power, and run in an additional power wire. I bought a box of the same connectors that the strings use, and made custom "Y" connectors that pass the signal wire through and bring in power, then run a wire back to the box. The wire I'm using is 18/3 "max bright led cable", but any decently jacketed for weatherproof 18/3 will do.

In photo, male towards right goes into the end of a string, the female to the left goes to the next string, and the extra jack on the bottom is one of the additional power lines from the box. Note that the green (signal) wire is connected through the string connectors, but is capped off going back to the box. I had already made this power wire as an "extension cord" for the whole string, but that layout wasn't effective.

If I were to start over, I'd simply put a 2-pin version of the same kind of connector onto the extra little wires sticking out at the start of the string, I'm sure that's what they're there for. I'd do this for half the strings, and bring a power wire out to every 2nd string.

Click here for early attempt video. It starts with a "border" test, but I hadn't yet gotten it to blank the "unused" bulbs between strings. You can see how ragged the right edge is due to the inconsistent bulb spacing. The rest of the pattern is simply tests I wrote trying to get to scrolling and such.

Here's a later attempt including lettering. It starts with full on white so as to test the power supply and wiring, you can see I really need to bring in more external power wires as the last row is definitely fainter and yellowish. Currently we have power taps at 2, 4, 6, 8. Follows my business name "Perennial" Vintners, where you can see the ragged look from the ill-spacing. (I had to create the entire character set by hand.) Follows is a snowfall that almost looks nice, and some more learning/test patterns.

As documented below, I gave up on FreeBSD and Perl, and now use Raspbian ("noobs") which came pre-loaded (it's just Linux, so I'm good here), and Python which is a terrible, terrible farce of a language, but - it has NeoPixel suport.

In a nutshell, I build an array by hand of the rows by bulb number so that I can simply loop through them as an array, and not have to worry about the unused bulbs between rows. e.g. first row we use bulb 0 through bulb 39, then there's a 2 bulb gap, then the next row is bulb 42 through 81, etc. Also this array tells us if we're going left-to-right or vice versa with a 1 or -1. This little array is at runtime turned into a single linear array so we can simply index through.

OutputArray = [
[ 0, 39, 1], # 2
[ 42, 81, -1], # 2
[ 84, 123, 1], # 2
[126, 165, -1], # 2
[168, 207, 1], # 1
[209, 248, -1], # 2
[251, 290, 1], # 2
[293, 332, -1], # 2
[335, 374, 1], # 2
[377, 416, -1], # 2
[419, 458, 1], # 2
[460, 499, -1] # 2
]

def buildtranslateary():
idx = 0
for i in range(len(OutputArray)):
if OutputArray[i][2] > 0:
for j in range(OutputArray[i][0], (OutputArray[i][1] + 1), OutputArray[i][2]):
TranslateIndexAry.insert(idx, j)
idx = idx + 1
else:
for j in range(OutputArray[i][1], (OutputArray[i][0] - 1), OutputArray[i][2]):
TranslateIndexAry.insert(idx, j)
idx = idx + 1

def just_fill(r, g, b):
rowlen = ((OutputArray[0][1] - OutputArray[0][0]) + 1)
collen = len(OutputArray) for j in range(collen):
for i in range(rowlen):
dark = (j * rowlen) + i
darkoffset = (TranslateIndexAry[dark])
pixels[darkoffset] = (r, g, b)
pixels.show()
You'll use the neopixel module:
pixels = neopixel.NeoPixel(pixel_pin, num_pixels, brightness=base_bright, auto_write=False, pixel_order=ORDER)

To autostart your program when the RPi boots (so you can run "headless"), be sure to get the program so that it will run simply by invoking it on the command line. You may to have to dork with the "shebang" syntax (the first line in the file with the "#!") in order to get it to kick off the correct python. Then add it to /etc/rc.local, which btw is run as root, which is necessary for this to work. (Python errors with "cannot create mailbox" or some other such useless msg if you try to do the neopixel module without root.)

From here, you're on your own, hope this helped you get going with your project!

Attempting to get python and NeoLights working.
Installed python, got 3.7
Following:
https://learn.adafruit.com/circuitpython-on-raspberrypi-linux/installing-circuitpython-on-raspberry-pi
I don't have 'apt-get', so am skipping that.
I have 'pip', not 'pip3'.
I'm operating as 'root' thus no 'sudo'.
sudo pip3 install --upgrade setuptools
sudo pip3 install --upgrade adafruit-python-shell
pkg install wget
rehash
wget https://raw.githubusercontent.com/adafruit/Raspberry-Pi-Installer-Scripts/master/raspi-blinka.py
python raspi-blinka.py
Says "none detected".
Blinka Exiting due to error: Non-Raspberry Pi board detected. This must be run on a Raspberry Pi
Other website had me do:
pip install rpi_ws281x
This happened Ok some hours ago, but now it's barfing on missing 'c' include files. Looking around, this seems to be a known problem with MacOS. Looks like some decls have been moved around and thus should no longer be looked for in the old no-longer-existing files. I will create empty files as they're called out in hopes this will fix it.
cd /usr/include
touch sys/sysmacros.h
mkdir linux
touch linux/ioctl.h
touch byteswap.h
touch linux/types.h
I give up - now it's asking for linux/spi/spidev.h which I'm sure won't be in other files. Deleted all the above.
More attempts I've stumbled through:
https://learn.adafruit.com/neopixels-on-raspberry-pi/python-usage
This one helped me get it wired. I know the string works as when I bought the string, I also got a little $18 controller that talks to your phone via bluetooth, specifically in order to be able to test it. I have not seen it light in this config, however the first problem is the above software issues.
https://www.youtube.com/watch?v=KJupt2LIjp4