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.. _esp32_pwm:
Pulse Width Modulation
======================
Pulse width modulation (PWM) is a way to get an artificial analog output on a
digital pin. It achieves this by rapidly toggling the pin from low to high.
There are two parameters associated with this: the frequency of the toggling,
and the duty cycle. The duty cycle is defined to be how long the pin is high
compared with the length of a single period (low plus high time). Maximum
duty cycle is when the pin is high all of the time, and minimum is when it is
low all of the time.
* More comprehensive example with all **16 PWM channels and 8 timers**::
from time import sleep
from machine import Pin, PWM
try:
F = 10000 # Hz
D = 65536 // 16 # 6.25%
pins = (2, 4, 12, 13, 14, 15, 16, 18, 19, 22, 23, 25, 26, 27, 32, 33)
pwms = []
for i, pin in enumerate(pins):
f = F * (i // 2 + 1)
d = min(65535, D * (i + 1))
pwms.append(PWM(pin, freq=f, duty_u16=d))
sleep(2 / f)
print(pwms[i])
finally:
for pwm in pwms:
try:
pwm.deinit()
except:
pass
Output is::
PWM(Pin(2), freq=10000, duty_u16=4096)
PWM(Pin(4), freq=10000, duty_u16=8192)
PWM(Pin(12), freq=20000, duty_u16=12288)
PWM(Pin(13), freq=20000, duty_u16=16384)
PWM(Pin(14), freq=30030, duty_u16=20480)
PWM(Pin(15), freq=30030, duty_u16=24576)
PWM(Pin(16), freq=40000, duty_u16=28672)
PWM(Pin(18), freq=40000, duty_u16=32768)
PWM(Pin(19), freq=50000, duty_u16=36864)
PWM(Pin(22), freq=50000, duty_u16=40960)
PWM(Pin(23), freq=60060, duty_u16=45056)
PWM(Pin(25), freq=60060, duty_u16=49152)
PWM(Pin(26), freq=69930, duty_u16=53248)
PWM(Pin(27), freq=69930, duty_u16=57344)
PWM(Pin(32), freq=80000, duty_u16=61440)
PWM(Pin(33), freq=80000, duty_u16=65535)
* Example of a **smooth frequency change**::
from time import sleep
from machine import Pin, PWM
F_MIN = 1000
F_MAX = 10000
f = F_MIN
delta_f = F_MAX // 50
pwm = PWM(Pin(27), f)
while True:
pwm.freq(f)
sleep(1 / f)
sleep(0.1)
print(pwm)
f += delta_f
if f > F_MAX or f < F_MIN:
delta_f = -delta_f
print()
if f > F_MAX:
f = F_MAX
elif f < F_MIN:
f = F_MIN
See PWM wave on Pin(27) with an oscilloscope.
Output is::
PWM(Pin(27), freq=998, duty_u16=32768)
PWM(Pin(27), freq=1202, duty_u16=32768)
PWM(Pin(27), freq=1401, duty_u16=32768)
PWM(Pin(27), freq=1598, duty_u16=32768)
...
PWM(Pin(27), freq=9398, duty_u16=32768)
PWM(Pin(27), freq=9615, duty_u16=32768)
PWM(Pin(27), freq=9804, duty_u16=32768)
PWM(Pin(27), freq=10000, duty_u16=32768)
PWM(Pin(27), freq=10000, duty_u16=32768)
PWM(Pin(27), freq=9804, duty_u16=32768)
PWM(Pin(27), freq=9615, duty_u16=32768)
PWM(Pin(27), freq=9398, duty_u16=32768)
...
PWM(Pin(27), freq=1598, duty_u16=32768)
PWM(Pin(27), freq=1401, duty_u16=32768)
PWM(Pin(27), freq=1202, duty_u16=32768)
PWM(Pin(27), freq=998, duty_u16=32768)
* Example of a **smooth duty change**::
from time import sleep
from machine import Pin, PWM
DUTY_MAX = 65535
duty_u16 = 0
delta_d = 256
pwm = PWM(Pin(27), freq=1000, duty_u16=duty_u16)
while True:
pwm.duty_u16(duty_u16)
sleep(2 / pwm.freq())
print(pwm)
if duty_u16 >= DUTY_MAX:
print()
sleep(2)
elif duty_u16 <= 0:
print()
sleep(2)
duty_u16 += delta_d
if duty_u16 >= DUTY_MAX:
duty_u16 = DUTY_MAX
delta_d = -delta_d
elif duty_u16 <= 0:
duty_u16 = 0
delta_d = -delta_d
PWM wave on Pin(27) with an oscilloscope.
Output is::
PWM(Pin(27), freq=998, duty_u16=0)
PWM(Pin(27), freq=998, duty_u16=256)
PWM(Pin(27), freq=998, duty_u16=512)
PWM(Pin(27), freq=998, duty_u16=768)
PWM(Pin(27), freq=998, duty_u16=1024)
...
PWM(Pin(27), freq=998, duty_u16=64512)
PWM(Pin(27), freq=998, duty_u16=64768)
PWM(Pin(27), freq=998, duty_u16=65024)
PWM(Pin(27), freq=998, duty_u16=65280)
PWM(Pin(27), freq=998, duty_u16=65535)
PWM(Pin(27), freq=998, duty_u16=65279)
PWM(Pin(27), freq=998, duty_u16=65023)
PWM(Pin(27), freq=998, duty_u16=64767)
PWM(Pin(27), freq=998, duty_u16=64511)
...
PWM(Pin(27), freq=998, duty_u16=1023)
PWM(Pin(27), freq=998, duty_u16=767)
PWM(Pin(27), freq=998, duty_u16=511)
PWM(Pin(27), freq=998, duty_u16=255)
PWM(Pin(27), freq=998, duty_u16=0)
* Example of a **smooth duty change and PWM output inversion**::
from utime import sleep
from machine import Pin, PWM
try:
DUTY_MAX = 65535
duty_u16 = 0
delta_d = 65536 // 32
pwm = PWM(Pin(27))
pwmi = PWM(Pin(32), invert=1)
while True:
pwm.duty_u16(duty_u16)
pwmi.duty_u16(duty_u16)
duty_u16 += delta_d
if duty_u16 >= DUTY_MAX:
duty_u16 = DUTY_MAX
delta_d = -delta_d
elif duty_u16 <= 0:
duty_u16 = 0
delta_d = -delta_d
sleep(.01)
print(pwm)
print(pwmi)
finally:
try:
pwm.deinit()
except:
pass
try:
pwmi.deinit()
except:
pass
Output is::
PWM(Pin(27), freq=5000, duty_u16=0)
PWM(Pin(32), freq=5000, duty_u16=32768, invert=1)
PWM(Pin(27), freq=5000, duty_u16=2048)
PWM(Pin(32), freq=5000, duty_u16=2048, invert=1)
PWM(Pin(27), freq=5000, duty_u16=4096)
PWM(Pin(32), freq=5000, duty_u16=4096, invert=1)
PWM(Pin(27), freq=5000, duty_u16=6144)
PWM(Pin(32), freq=5000, duty_u16=6144, invert=1)
PWM(Pin(27), freq=5000, duty_u16=8192)
PWM(Pin(32), freq=5000, duty_u16=8192, invert=1)
...
See PWM waves on Pin(27) and Pin(32) with an oscilloscope.
Note: New PWM parameters take effect in the next PWM cycle.
pwm = PWM(2, duty=512)
print(pwm)
>>> PWM(Pin(2), freq=5000, duty=1023) # the duty is not relevant
pwm.init(freq=2, duty=64)
print(pwm)
>>> PWM(Pin(2), freq=2, duty=16) # the duty is not relevant
time.sleep(1 / 2) # wait one PWM period
print(pwm)
>>> PWM(Pin(2), freq=2, duty=64) # the duty is actual
Note: machine.freq(20_000_000) reduces the highest PWM frequency to 10 MHz.
Note: the Pin.OUT mode does not need to be specified. The channel is initialized
to PWM mode internally once for each Pin that is passed to the PWM constructor.
The following code is wrong::
pwm = PWM(Pin(5, Pin.OUT), freq=1000, duty=512) # Pin(5) in PWM mode here
pwm = PWM(Pin(5, Pin.OUT), freq=500, duty=256) # Pin(5) in OUT mode here, PWM is off
Use this code instead::
pwm = PWM(Pin(5), freq=1000, duty=512)
pwm.init(freq=500, duty=256)
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