import machine, neopixel, time

N = 12
p = machine.Pin(11)
np = neopixel.NeoPixel(p, N, bpp=3, timing=1)

n = 0
dn = 1

while(1):
    if(n == 11):
        dn = -1
    if(n == 0):
        dn = +1
    n += dn
    np.fill([0,0,0])
    np[n] = (50,0,0)
    np.write()
    time.sleep(0.1)