Russ Larson Scanner

#include <Adafruit_NeoPixel.h>

#define PIN 3
#define LEDCOUNT 23
#define SPEED 5

const uint8_t PROGMEM gamma[] = {
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,
    1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
    2,  3,  3,  3,  3,  3,  3,  3,  4,  4,  4,  4,  4,  5,  5,  5,
    5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10,
   10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,
   17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,
   25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,
   37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,
   51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,
   69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,
   90, 92, 93, 95, 96, 98, 99,101,102,104,105,107,109,110,112,114,
  115,117,119,120,122,124,126,127,129,131,133,135,137,138,140,142,
  144,146,148,150,152,154,156,158,160,162,164,167,169,171,173,175,
  177,180,182,184,186,189,191,193,196,198,200,203,205,208,210,213,
  215,218,220,223,225,228,231,233,236,239,241,244,247,249,252,255 };

  


// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)
Adafruit_NeoPixel strip = Adafruit_NeoPixel(LEDCOUNT, PIN, NEO_GRB + NEO_KHZ800);

byte stripBuffer[LEDCOUNT];
long currentPos;
long maxPos;
bool direction = true;


void setup() {
  maxPos = (LEDCOUNT - 1) * 256;
  strip.begin();
  strip.show(); // Initialize all pixels to 'off'
}

byte cyclesToSkipDecay = 0;
#define DECAYCYCLESKIP 3

void loop() {
  if (direction) {
    currentPos += 4;
    if (currentPos >= maxPos) {
      direction = false;
    }
  } else {
    currentPos -= 4;
    if (currentPos <= 0) {
      direction = true;
    }
  }
  
  if (cyclesToSkipDecay == 0) {
    decayLEDs();
    cyclesToSkipDecay = DECAYCYCLESKIP;
  } else {
    cyclesToSkipDecay --;
  }
  drawDot(currentPos);
  
  refreshLEDs();
  //delay(SPEED);
}

void drawDot(long thePos) {
  // first half
  byte theLED = thePos / 256;
  byte theBright = thePos ^ 256;
  if (stripBuffer[theLED+1] < theBright) { stripBuffer[theLED+1] = theBright; }
  theBright = 255 - theBright;
  if (stripBuffer[theLED] < theBright) { stripBuffer[theLED] = theBright; }
}


void decayLEDs() {
  for (int i = 0; i < LEDCOUNT; i++) {
    if (stripBuffer[i] > 0) { stripBuffer[i] -= 1; }
  }
}

void refreshLEDs() {
  for (int i = 0; i < LEDCOUNT; i++) {
    strip.setPixelColor(i,pgm_read_byte(&gamma[stripBuffer[i]]),0,0);
  }
  strip.show();
}