First custom led system integrated in model kit

Greetings everyone,

I’m fairly new when it comes to all this stuf but I do have some experience of creating some simple arduino projects thanks to school assignments and building a few kits like a path finding car. My problem these kits and assignments where all laid out and I have never created my own project and to be honest its been a while since I last touched something like an arduino.

I do like to build plastic model kits like Gundams and have done some custom jobs like adding standard LEDs into them but these are just directly wired to a batttery some they just turn on and off. For my next project i would like to step up my game and create a little custom led system. My plan is to illuminate 3 zones using (something like, open for suggestions) adafruits WS2812B Digitale 5050 RGB LED Neopixels (See attachment for spec).
2 zones will get 2 NeoPixels and the 3rd zone will get 3 Neopixels, so a total of 7 neopixels will be used. The nice thing with this neopixels is the data in and out build into the leds so i only need one data cable to each zone.

I would like to build this right into the model so I have been looking for some of the smaller micro controllers like the Seeeduino XIAO (https://www.seeedstudio.com/Seeeduino-XIAO-Arduino-Microcontroller-SAMD21-Cortex-M0+-p-4426.html) or the dfrobot beetle (https://www.dfrobot.com/product-1075.html). For power, since I do not want any wires comming out of the kit I’m thinking of using a small 3.7 li-po battery. As last i might add a button or two, one for power and one to cycle through different light modes.

As I mentioned this would be my first custom arduino project so I would like to ask you guys for advice. One thing I’m especially worried about is the wiring, my idea would be to create multiple splits to connect power and ground to all the components (the controller and to each of the 7 neopixels). As far as I’m aware i need to connect the neopixels directly to the power supply. So my going from the battery, a split to the micro controller and the other end would split into the 3 ways, one for each of the zones which in turn would be split for the leds. Would this work and is it save to split power and ground multiple times like this?

Another thing i cannot figure out is if and what kind of resitors i would need for the neopixels.

I am open for suggestions and please let me know if you know some other components which might be beter suited.

Thank you in advance.

WS2812B datasheet.pdf (338 KB)

For WS2812 LED strips it is easier if you use a 5V processor to control the 5V strips.

Using the FastLED library you can have an independent controller (zone) for each strip. Each strip should have a 470 Ohm (or so) resistor in series between the output pin and Din of the strip.

Each strip can have its own feed and ground from the 5V supply.

Place a 1000uF cap where the 5V feed goes out to the strips to smooth out current fluctuations on the 5V supply.

If I have several controllers (zones) I would make an array of controllers. Can make it easier to handle.

Thanks for the reply,

In my post I am actually talking about the single NeoPixels, not the strips or on a pcb. But i will look into those strips since they could be cut to length and i could solder some wires and connectors between them.

helios27:
In my post I am actually talking about the single NeoPixels, not the strips or on a pcb. But i will look into those strips since they could be cut to length and i could solder some wires and connectors between them.


Aliexpress link

You can still use a lipo if you switch to 5 volts, which as @groundFungus points out will make things way easier.

Use a 5 volt boost regulator of appropriate capacity. Polulo.com has quite few, they can be found cheaper. Specifications tend to be, um, optimistic, so get one that has plenty of current output. Doubling your expected current draw for selecting a particular boost converter is no unreasonable.

Neopixels can use 60 mA each at full brightness. But that is really quite bright and would only add up to a large current if all LEDs were fully on. So you may want to use an external 5 volt power supply to get an idea of what your current requirement will be empirically, then select the boost. I often come no where near needing the theoretical maximum current, but I tend to do chasers with a small fraction of the lights on at lower brightness. YMMV as is said.

The LEDs can all be run off one output pin - you could use one strip (one strip object, one i/o pin) and just know in the code that LEDs 0, 1 and 2 go with region A and 3 and 4 are for region B and so forth. Arrays can be used for this: if you haven’t already it is never to early too start figuring out array variables. We can help, natch.

a7

If you only have 7 of them, consider making them all as one string.
Need 420mA total if all 7 are on full bright, just need a single 1A supply to power all that.
Put a buffer chip between the 3.3V data pin source and the 5V input pin.

Is this too small for you to handle?
https://www.digikey.com/en/products/detail/diodes-incorporated/74AHCT1G32SE-7/2711987

@xRoads nice trick, I’ll try to remember these chips.

If you do stick with 3.3 volts, there’s this hack

which I cannot vouch for but looks plausible. It still uses 5 volts for the real LEDs however. I don’t know how far you get powering neos with 3.6 to 4.2 volts, the range your lipo will cover whilst delivering to you most of its charge. An experiment would be determinitave.

I am compelled to remind everyone that lipo batteries are the neediest of all chemistries, you want to be sure to treat them better than you treat your mother.

a7

My original plan was to run 7 individual neopixels (single pixels, no strips) and power them directly from a power source. Still looking into it but i might be able to get away with 5. I want to route 2 pixels one way, 2 pixels another direction and 1/3 yet another way so i cannot use a strip or hook them up in a single line.

I looked around a bit for other possible micro controllers and tutorials using the WS2812 neopixels and found the following tutorial: Overview | Color Mixing QT Py Cuff Bracelet | Adafruit Learning System.

This uses adafruit QT PY micro controller (similar to the seeeduino XIAO) and they connect a 3.7v battery to the QT PY for power and run 2 ws2812 led strips from the 5v header of the micro controller itself without any extra chips or resitors. Would this actually work?

If so could i also do the same for my project? Could i hookup a 3.7v battery to the micro controller and run 7 individual neopixels from the 5v header of the controller itself. I known because of the 3.7 v battery they might not but full brightness but i don’t think i need them at full brightness.

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