Here is another channel upper and lower bands indicator, this one is made of a centered Triangular Moving Average with classic deviation from this mean, made of plus and minus ATR multiplicated value. Quiet popular in the forex trading community, it is the base of many more or less sophisticated strategy, do your homework with this one, you’ll find it is valuable for different market phase.
// parameters
// HalfLength = 50
// AtrLength = 100
// AtrMultiplier = 2.0
avg = average[1](close)
sum = (HalfLength+1)*avg
sumw = (HalfLength+1)
k = HalfLength
for j = 1 to HalfLength do
k = k-1
sum = sum+(k*avg[j])
sumw = sumw+k
next
buffer1 = sum/sumw
myrange = AverageTrueRange[AtrLength](close)*AtrMultiplier
buffer2 = buffer1+myrange
buffer3 = buffer1-myrange
RETURN buffer1 coloured(0,220,0) as "TMA", buffer2 coloured(220,0,0) as "upper band", buffer3 coloured(0,220,0) as "lower band"