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After checking that the "Face shield" and 8x8 WS2812B matrix (10 x 10 cm) nicely fit together at the size, I found the substrate of the LED matrix is a little bit visible by its light.So I decided to have a light diffuser for hiding it. Since the matrix tightly fits to the curved surface of the face shield, the diffuser must be flexible too. 

It's time to launch OpenSCAD.

The diffuser consists of "cells" for each WS2812B pixel and "tabs" which connect between "cells". Because the "tabs" are thin and have been printed with PLA, the structure got some flexibility.

Let's assemble the diffuser and LED matrix and put a piece of paper on it for checking.

Looks fine. Then the last thing to be done is pasting them together with some glue.

It's a prototyping, so I allowed myself to use a ton of tapes to fix this assembly onto the face shield. (Hey, no need to feel guilty, even Apple uses tapes and glue in their products.)

Wrote a test sketch to a beloved Digispark clone, now it started blinking.

$ mkdir firmware
$ pio init -b digispark-tiny -d firmware
$ code firmware
$ code firmware/platformio.ini

[env:digispark-tiny]
platform = atmelavr
board = digispark-tiny
framework = arduino

lib_deps =
  https://github.com/adafruit/Adafruit_NeoPixel
  https://github.com/SofaPirate/Chrono#390c2ee

#include <Chrono.h>
Chrono blinkTask;

#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
#include <avr/power.h>
#endif

#define PIN 1
#define NUMPIXELS 64

Adafruit_NeoPixel pixels(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);

uint16_t hue = 200;
int16_t saturation = 200;
int16_t brightness = 10;

const uint8_t face1[] = {0b0,        0b11000011, 0b11000011, 0b11000011,
                         0b11000011, 0b11000011, 0b11000011, 0b0};
const uint8_t blink_frame_0[] = {0b0,        0b0,        0b11000011, 0b11000011,
                                 0b11000011, 0b11000011, 0b0,        0b0};
const uint8_t blink_frame_1[] = {0b0,        0b0, 0b0, 0b11000011,
                                 0b11000011, 0b0, 0b0, 0b0};
const uint8_t blink_frame_2[] = {0b0, 0b0, 0b0, 0b11000011, 0b0, 0b0, 0b0, 0b0};

const uint8_t face2[] = {0b10000001, 0b01000010, 0b00100100, 0b00011000,
                         0b00011000, 0b00100100, 0b01000010, 0b10000001};

void drawFrame(const uint8_t frame[]) {
    for(int i = 0; i < NUMPIXELS; i++) {
        uint8_t rowInd = i / 8;
        uint8_t row = frame[rowInd];
        uint8_t colInd = i % 8;
        if(rowInd % 2) { // reversing for the Zig-zag alignment
            colInd = 7 - colInd;
        }
        uint8_t bit = (row >> (7 - colInd)) & 0b1;
        pixels.setPixelColor(i, pixels.ColorHSV(hue, saturation, bit ? 20 : 0));
    }
}

void randomColors() {
    for(int i = 0; i < NUMPIXELS; i++) {
        pixels.setPixelColor(
            i, pixels.ColorHSV(rand() % UINT16_MAX, 200 + rand() % 50, 100));
    }
    pixels.show();
}

void blink() {
    const uint8_t *frames[] = {blink_frame_0, blink_frame_1, blink_frame_2,
                               NULL,          blink_frame_1, blink_frame_0};

    for(auto &&i : frames) {
        if(i == NULL) {
            pixels.clear();
            continue;
        }
        drawFrame(i);
        pixels.show();
        delay(30);
    }
}

void setup() {
    clock_prescale_set(clock_div_1);
    pixels.begin();

    for(int i = 0; i < NUMPIXELS; i++) {
        uint16_t hue_ = rand() % UINT16_MAX;
        for(size_t j = 0; j < brightness; j += 3) {
            pixels.setPixelColor(i, pixels.ColorHSV(hue_, saturation, j));
            if(i) {
                pixels.setPixelColor(i - 1,
                                     pixels.ColorHSV(hue_, saturation, 0));
            }
            pixels.show();
            delay(5);
        }
    }
}

void loop() {
    hue = hue + 1 % 655535;

    drawFrame(face1);
    pixels.show();

    if(blinkTask.hasPassed(2000)) {
        blinkTask.restart();
        blink();
    }
}