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--- 12_neopixel_led_strip [2026/08/01 18:21] – walkeradmin
+++ 12_neopixel_led_strip [2026/08/02 13:48] (current) – [Knight Rider Lights] walkeradmin
@@ Line 337: / Line 337: @@
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 The NeoPixel in Wokwi isn't perfect, but it illustrates that the project will function as expected.
+\\
+\\
+----
+==== NeoPixel LED Chase Sequence ====
+This next code scrolls down the line of NeoPixels. The most important line of code in this example is this:
+  * for i in range(NUM_LEDS):
+What this does is creates a range of numbers from the value of the NUM_LEDS (12 in our example) and this looks like this:
+  * 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
+So this for loop starts at '0' and does the following:
+<code:python | download>
+for i in range(NUM_LEDS):    # get the num range (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
+        clear()              # call the clear function to turn off all leds
+        np[i] = color        # set the color of first LED
+        np.write()           # write the LED status
+        time.sleep(delay)    # wait for delay time.
+        # now the loop will do the same but for LED2, 3, 4 etc.
+        # we clear the LEDs each time so that only 1 LED is ever illuminated.
+</code>
+We call this chase function 3 times:
+<code:python | download>
+    # Chase effect
+    chase((255, 0, 0), 0.08)
+    chase((0, 255, 0), 0.08)
+    chase((0, 0, 255), 0.08)
+</code>
+First we set LEDs to Red, then second time it's Green then lastly we set Blue.
+Here is the full code:
+<code:python | download>
+# WS2812 / NeoPixel Example
+# Raspberry Pi Pico + MicroPython
+#
+# Controls a strip of 12 LEDs connected to GP0.
+from machine import Pin
+import neopixel
+import time
+# -------------------------------
+# Configuration
+# -------------------------------
+LED_PIN = 8          # GPIO connected to DIN
+NUM_LEDS = 12        # Number of LEDs, 0-11 is used, not 1-12
+# Create the NeoPixel object
+np = neopixel.NeoPixel(Pin(LED_PIN), NUM_LEDS)
+# -------------------------------
+# Helper Functions
+# -------------------------------
+def clear():
+    """Turn all LEDs off."""
+    for i in range(NUM_LEDS):
+        np[i] = (0, 0, 0)
+    np.write()
+def chase(color, delay=1):
+    """Move one LED along the strip."""
+    clear()
+    for i in range(NUM_LEDS):
+        clear()
+        np[i] = color
+        np.write()
+        time.sleep(delay)
+# -------------------------------
+# Main Program
+# -------------------------------
+while True:
+    # Chase effect
+    chase((255, 0, 0), 0.08)
+    chase((0, 255, 0), 0.08)
+    chase((0, 0, 255), 0.08)
+</code>
+Here is a short video showing the sequence.
+\\
+\\
+{{ :neopixel-chase-led-example-001.mp4?640 |}}
+\\
+It's a nice effect to see the LEDs chasing like this.
+\\
+\\
+----
+==== Knight Rider Lights ====
+Who remembers these?
+\\
+\\
+{{ :knight-rider-001.mp4?640 |}}
+\\
+Well I do :) and we can replicate this effect with our Pico and NeoPixel LEDs. The code for this is almost identical to the previous project where we have the running LEDs.
+\\
+\\
+The major change is the addition of this part:
+<code:python | download>
+    # Backward direction
+    for i in range(NUM_LEDS - 2, 0, -1):
+        clear()
+        np[i] = color
+        np.write()
+        time.sleep(delay)
+</code>
+In our previous project, the LEDs ran forward, then cycled colour, in this project we are not cycling the colour and the additional code runs the LEDs in reverse.
+\\
+\\
+Here is the full code, explanation for how this works is at the end of this wiki page.
+<code:python | download>
+# WS2812 / NeoPixel Example
+# Raspberry Pi Pico + MicroPython
+#
+# Controls a strip of 12 LEDs connected to GP8.
+from machine import Pin
+import neopixel
+import time
+# -------------------------------
+# Configuration
+# -------------------------------
+LED_PIN = 8          # GPIO connected to DIN
+NUM_LEDS = 12        # Number of LEDs, 0-11 is used, not 1-12
+# Create the NeoPixel object
+np = neopixel.NeoPixel(Pin(LED_PIN), NUM_LEDS)
+# -------------------------------
+# Helper Functions
+# -------------------------------
+def clear():
+    """Turn all LEDs off."""
+    for i in range(NUM_LEDS):
+        np[i] = (0, 0, 0)
+    np.write()
+def chase_bounce(color, delay=0.1):
+    """Move one LED up and down the strip."""
+    # Forward direction
+    for i in range(NUM_LEDS):
+        clear()
+        np[i] = color
+        np.write()
+        time.sleep(delay)
+    # Backward direction
+    for i in range(NUM_LEDS - 2, 0, -1):
+        clear()
+        np[i] = color
+        np.write()
+        time.sleep(delay)
+# -------------------------------
+# Main Program
+# -------------------------------
+while True:
+    # Chase effect
+    chase_bounce((255, 0, 0), 0.08)
+</code>
+So, what does this extra code do? and how?
+\\
+\\
+Here is an explanation of the reverse code block in general.
+<code:python | download>
+# Backward direction (move the lit LED from right to left)
+# range(NUM_LEDS - 2, 0, -1) generates:
+# For 12 LEDs → 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
+# - Start at LED 10 (second-to-last)
+# - Stop at LED 1 (LED 0 is skipped to avoid repeating the end LED)
+# - Step backwards by -1 each time
+for i in range(NUM_LEDS - 2, 0, -1):
+    clear()              # Turn all LEDs off before lighting the next one
+    np[i] = color        # Light the current LED at position i
+    np.write()           # Send the updated LED data to the strip
+    time.sleep(delay)    # Pause so the movement is visible
+</code>
+And this is what the line that makes the count to backwards actually does.
+<code:python | download>
+range(NUM_LEDS - 2, 0, -1)
+#Breakdown for NUM_LEDS = 12:
+Start: NUM_LEDS - 2 → 10
+#(LED 11 was already lit in the forward chase)
+Stop: 0
+#(but Python stops before 0, so last value is 1)
+Step: -1
+#(count backwards)
+</code>
+For the reverse sequence, we don't need to worry about the first (0) or last (11) LEDs as these are already set by the forward sequence.
+\\
+\\
+That's it! Oh, and don't worry, I won't be fitting these to my car :)
+\\
+\\
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