1 files changed, 38 insertions, 0 deletions
diff --git a/examples/hwapi/soft_pwm.py b/examples/hwapi/soft_pwm.py
new file mode 100644
index 0000000000..a9a5561717
--- /dev/null
+++ b/examples/hwapi/soft_pwm.py
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+import utime
+from hwconfig import LED
+
+
+# Using sleep_ms() gives pretty poor PWM resolution and
+# brightness control, but we use it in the attempt to
+# make this demo portable to even more boards (e.g. to
+# those which don't provide sleep_us(), or provide, but
+# it's not precise, like would be on non realtime OSes).
+# We otherwise use 20ms period, to make frequency not less
+# than 50Hz to avoid visible flickering (you may still see
+# if you're unlucky).
+def pwm_cycle(led, duty, cycles):
+    duty_off = 20 - duty
+    for i in range(cycles):
+        if duty:
+            led.value(1)
+            utime.sleep_ms(duty)
+        if duty_off:
+            led.value(0)
+            utime.sleep_ms(duty_off)
+
+
+# At the duty setting of 1, an LED is still pretty bright, then
+# at duty 0, it's off. This makes rather unsmooth transition, and
+# breaks fade effect. So, we avoid value of 0 and oscillate between
+# 1 and 20. Actually, highest values like 19 and 20 are also
+# barely distinguishible (like, both of them too bright and burn
+# your eye). So, improvement to the visible effect would be to use
+# more steps (at least 10x), and then higher frequency, and use
+# range which includes 1 but excludes values at the top.
+while True:
+    # Fade in
+    for i in range(1, 21):
+        pwm_cycle(LED, i, 2)
+    # Fade out
+    for i in range(20, 0, -1):
+        pwm_cycle(LED, i, 2)