larson scanner with neopixel led strip. the gist is for each loop to decay al the leds in the strip, and then add a moving full-on led. example here: https://www.youtube.com/watch?v=htmgPjYIphI

larson_scanner.ino

#Using an Adafruit NeoPixel led strip http://www.adafruit.com/product/1138

#include <Adafruit_NeoPixel.h>

#define MAX_P 60

// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type flags, add together as needed:
//   NEO_RGB     Pixels are wired for RGB bitstream
//   NEO_GRB     Pixels are wired for GRB bitstream
//   NEO_KHZ400  400 KHz bitstream (e.g. FLORA pixels)
//   NEO_KHZ800  800 KHz bitstream (e.g. High Density LED strip)
Adafruit_NeoPixel strip = Adafruit_NeoPixel(MAX_P, 6, NEO_GRB + NEO_KHZ800);
int li=0;
int direction=+1;

uint32_t Red=strip.Color(255, 0, 0);
uint32_t Blank=strip.Color(0, 0, 0);
void setup() {
  strip.begin();
  strip.show(); // Initialize all pixels to 'off'
}

void loop() {
	//decay
	for(uint16_t i=0; i<MAX_P; i++) {
		uint8_t r= (strip.getPixelColor(i)>>16) & 0xff;
		r=(r*3)/5;
  		strip.setPixelColor(i, r, 0, 0);
	}

	strip.setPixelColor(li, Red);
	if(li>(MAX_P-1)){
		li=MAX_P;
		direction=-1;
	}else if(li<0){
		li=-1;
		direction=1;
	}
	li+=direction;
	strip.show();
	delay(10);
}