Arcade button lighting on an ESP32-C3

// Button lights: each arcade button lights its own pair of WS2812B LEDs.
//
// Wiring:
//   buttons  1 on GPIO 0   2 on GPIO 1   3 on GPIO 10   4 on GPIO 4
//            (other leg of each to GND, internal pull-up on, pressed = LOW)
//   strip    DIN -> GPIO 5   VDD -> 5 V   VSS -> GND
//
// Eight LEDs on one wire, two under each button. A press lights that
// button's pair at full color at once; letting go fades it out over a few
// frames, which is the "reactive" lighting many custom controllers ship with.
//
// Why an ESP32-C3 and not a Pro Micro or a Pico: a WS2812 bit is a pulse a
// few hundred nanoseconds long. Real 32U4 boards make it with hand-written
// assembly (FastLED, the Adafruit library) and the RP2040 with its PIO
// blocks. Mokxi runs WS2812 strips from the ESP32-C3 and ESP32-C6 only, so
// this circuit uses the C3. The lighting logic below is the same on any
// board; only the driver underneath changes.
//
// The button reading is the same pull-up pattern as the fight stick
// examples, and the lights never slow it down: a frame is drawn at most
// every FRAME_MS, and the buttons are read on every pass of loop().

#include <Adafruit_NeoPixel.h>

const uint8_t DIN_PIN = 5;
const uint8_t LEDS = 8;
const uint8_t BUTTONS = 4;
const uint8_t BUTTON_PINS[BUTTONS] = {0, 1, 10, 4};

// One color per button, as 0..255 red, green, blue.
const uint8_t COLORS[BUTTONS][3] = {
  {255, 40, 40},   // 1: red
  {40, 120, 255},  // 2: blue
  {40, 255, 80},   // 3: green
  {255, 200, 30},  // 4: yellow
};

// How much of the light is left after each frame once a button is let go,
// out of 256. 200 is a quick fade of a few tenths of a second.
const uint16_t FADE = 200;
const unsigned long FRAME_MS = 16;

Adafruit_NeoPixel strip(LEDS, DIN_PIN, NEO_GRB + NEO_KHZ800);

// Each button's brightness, 0..255.
uint8_t level[BUTTONS];
bool wasHeld[BUTTONS];
unsigned long lastFrame = 0;

void setup() {
  Serial.begin(115200);
  for (uint8_t i = 0; i < BUTTONS; i++) {
    pinMode(BUTTON_PINS[i], INPUT_PULLUP);
  }
  strip.begin();
  strip.clear();
  strip.show();
  Serial.println("Button lights: press the arcade buttons.");
}

void loop() {
  for (uint8_t i = 0; i < BUTTONS; i++) {
    bool held = digitalRead(BUTTON_PINS[i]) == LOW;
    if (held) {
      level[i] = 255;  // on at once, on the same pass the press was seen
    }
    if (held != wasHeld[i]) {
      wasHeld[i] = held;
      Serial.print("button ");
      Serial.print(i + 1);
      Serial.println(held ? " down" : " up");
    }
  }

  unsigned long now = millis();
  if (now - lastFrame < FRAME_MS) {
    return;
  }
  lastFrame = now;

  for (uint8_t i = 0; i < BUTTONS; i++) {
    uint8_t r = (uint8_t)((COLORS[i][0] * (uint16_t)level[i]) >> 8);
    uint8_t g = (uint8_t)((COLORS[i][1] * (uint16_t)level[i]) >> 8);
    uint8_t b = (uint8_t)((COLORS[i][2] * (uint16_t)level[i]) >> 8);
    strip.setPixelColor(i * 2, r, g, b);
    strip.setPixelColor(i * 2 + 1, r, g, b);
    if (!wasHeld[i]) {
      level[i] = (uint8_t)((level[i] * FADE) >> 8);
    }
  }
  strip.show();
}