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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.on()
- utime.sleep_ms(duty)
- if duty_off:
- led.off()
- 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)
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