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