diff --git a/pico/test/rainbow.py b/pico/test/rainbow.py
new file mode 100644
index 0000000..a00b916
--- /dev/null
+++ b/pico/test/rainbow.py
@@ -0,0 +1,94 @@
+import sys
+# So "from ws2812 import WS2812B" finds pico/lib when run from device / or test/
+if "lib" not in sys.path:
+    sys.path.insert(0, "lib")
+if "../lib" not in sys.path:
+    sys.path.insert(0, "../lib")
+from ws2812 import WS2812B
+import time
+
+# --- Rainbow pattern (outside ws2812): pregen double buffer, show via head offset ---
+
+def hue_to_rgb(hue):
+    """Hue 0..360 -> (r, g, b). Simple HSV with S=V=1."""
+    h = hue % 360
+    x = 1 - abs((h / 60) % 2 - 1)
+    if h < 60:
+        r, g, b = 1, x, 0
+    elif h < 120:
+        r, g, b = x, 1, 0
+    elif h < 180:
+        r, g, b = 0, 1, x
+    elif h < 240:
+        r, g, b = 0, x, 1
+    elif h < 300:
+        r, g, b = x, 0, 1
+    else:
+        r, g, b = 1, 0, x
+    return (int(r * 255), int(g * 255), int(b * 255))
+
+
+def make_rainbow_double(num_leds, brightness=1.0):
+    """Build 2 full rainbow cycles (2*num_leds pixels, GRB). Returns (double_buf, strip_len).
+    head must be in 0..strip_len-1 so DMA reads double_buf[head:head+strip_len] with no copy."""
+    n = 2 * num_leds
+    double_buf = bytearray(n * 3)
+    for i in range(n):
+        hue = (i / n) * 360 * 2
+        r, g, b = hue_to_rgb(hue)
+        g = int(g * brightness) & 0xFF
+        r = int(r * brightness) & 0xFF
+        b = int(b * brightness) & 0xFF
+        o = i * 3
+        double_buf[o] = g
+        double_buf[o + 1] = r
+        double_buf[o + 2] = b
+    strip_len = num_leds * 3
+    return (double_buf, strip_len)
+
+
+def show_rainbow(strip, double_buf, strip_len, head):
+    """DMA reads directly from double_buf at head; no copy. head in 0..strip_len-1."""
+    strip.show(double_buf, head)
+
+
+# --- Strips + rainbow buffers per strip ---
+
+strips = []
+pins = ((2, 291), 
+        (3, 290), 
+        (4, 283), 
+        (7, 278),
+        (0, 275), 
+        (28, 278),
+        (29, 283),
+        (6, 290))
+sm = 0
+for pin, num_leds in pins:
+    print(pin, num_leds)
+    ws = WS2812B(num_leds, pin, sm, brightness=1.0)  # 1.0 so fill() is visible
+    strips.append(ws)
+    sm += 1
+
+# One rainbow double buffer per strip (num_leds can differ); no transfer buffer
+now = time.ticks_ms()
+rainbow_data = [make_rainbow_double(ws.num_leds, ws.brightness) for ws in strips]
+# Cumulative LEDs before each strip so rainbow lines up around the ring
+cumulative_leds = [0]
+for ws in strips[:-1]:
+    cumulative_leds.append(cumulative_leds[-1] + ws.num_leds)
+# Global phase (bytes); each strip gets head = (phase + cumulative_leds * 3) % strip_len
+total_ring_leds = cumulative_leds[-1] + strips[-1].num_leds
+bytes_per_cycle = total_ring_leds * 3
+print(time.ticks_diff(time.ticks_ms(), now), "ms")
+rainbow_head = 0
+step = 3
+
+while True:
+    now = time.ticks_ms()
+    for i, (strip, (double_buf, strip_len)) in enumerate(zip(strips, rainbow_data)):
+        head = (rainbow_head + cumulative_leds[i] * 3) % strip_len
+        show_rainbow(strip, double_buf, strip_len, head)
+    rainbow_head = (rainbow_head + step) % bytes_per_cycle
+    #print(time.ticks_diff(time.ticks_ms(), now), "ms")
+    time.sleep_ms(10)