Merge pull request adafruit#1271 from adafruit/TheKitty-patch-2

Code for QT Py Bracelet tutorial

Author: TheKitty

QT_Py_Bracelet/README.md

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+## Color Mixing QT Py Cuff Bracelet
+
+This directory contains code for the Adafruit Learning System tutorial Color Mixing QT Py Cuff Bracelet by Debra Ansell.
+
+https://learn.adafruit.com/color-mixing-qt-py-cuff/
+
+Coded in CircuitPython
+
+MIT Licensed, support Open Source by buying products from Adafruit.com

QT_Py_Bracelet/code.py

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+# Demo code to generate an alternating color-gradient effect in
+# the QT Py LED cuff bracelet LEDs.
+import time
+import board
+import neopixel
+
+# Total number of LEDs on both strips
+NUM_PIXELS = 14
+
+pixels = neopixel.NeoPixel(board.MOSI, NUM_PIXELS, pixel_order=neopixel.GRB, auto_write=False, brightness = 0.4
+)
+
+def wheel(pos):
+    # Input a value 0 to 255 to get a color value.
+    # The colours are a transition r - g - b - back to r.
+    if pos < 0 or pos > 255:
+        return (0, 0, 0)
+    if pos < 85:
+        return (255 - pos * 3, pos * 3, 0)
+    if pos < 170:
+        pos -= 85
+        return (0, 255 - pos * 3, pos * 3)
+    pos -= 170
+    return (pos * 3, 0, 255 - pos * 3)
+    
+# Scales a tuple by a fraction of 255
+def scale(tup, frac):
+    return tuple((x*frac)//255 for x in tup)
+
+# Sawtooth function with amplitude and period of 255
+def sawtooth(x):
+    return int(2*(127.5 - abs((x % 255) - 127.5)))
+
+# Hue value at the opposite side of the color wheel
+def oppositeHue(x):
+    return ((x + 128) % 256)
+
+hueIndex = 0         # determines hue value (0->255)
+brightnessIndex = 0  # input to the sawtooth function for determining brightness (0->255)
+brightnessSpeed = 3  # bigger value = faster shifts in brightness
+
+while True:
+    bright = sawtooth(brightnessIndex)
+    
+    # get RGB color from wheel function and scale it by the brightness
+    mainColor = scale(wheel(hueIndex),bright)
+    oppColor = scale(wheel(oppositeHue(hueIndex)), 255 - bright)
+
+    # hue and brightness alternate along each strip
+    for i in range(NUM_PIXELS//2):
+        pixels[i*2] = mainColor
+        pixels[i*2 + 1] = oppColor
+    pixels.show()
+    
+    # increment hue and brightness
+    hueIndex = (hueIndex + 1) % 255        
+    brightnessIndex = (brightnessIndex + brightnessSpeed) % 255