Comments on: ESP32/ESP8266 PWM with MicroPython – Dim LED

By: gou ru vernooij

gou ru vernooij — Fri, 15 Oct 2021 12:33:26 +0000

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By: Sara Santos

Sara Santos — Sat, 19 Dec 2020 12:03:19 +0000

In reply to Dušan.

Hi.
It seems that different frequencies are not supported in MicroPython. Read this: https://github.com/micropython/micropython/blob/0fff2e03fe07471997a6df6f92c6960cfd225dc0/docs/esp8266/quickref.rst#pwm-pulse-width-modulation
And this: https://github.com/micropython/micropython/pull/3608
Regards,
Sara

By: Dušan

Dušan — Fri, 18 Dec 2020 22:44:04 +0000

In reply to Dušan.

Now I have tested different versions of MicroPython (1.9, 1.13 IDF3) and also ESP8266 – it is all the same. :-/ It means that I have to use machine.Timer() with 4 channels available and create my own pwm class?

For higher frequencies it is also possible to use 8× RMTs on ESP32, but it is not so easy to set precise frequency. We may use it for LEDs:
import esp32
from machine import Pin, PWM
ledR = esp32.RMT(0, pin = Pin(13))
ledR.loop(True)
ledY = esp32.RMT(1, pin = Pin(12))
ledY.loop(True)
ledG = esp32.RMT(2, pin = Pin(14))
ledG.loop(True)

duties:

ledR.write_pulses((50, 50)) # 50:50 = 50 %
ledY.write_pulses((10, 90)) # 10:90 = 10 %
ledG.write_pulses((100, 0)) # 100:0 = 100 %
ledB = PWM(Pin(2), freq = 5, duty = 50)

In fact those write_pulses values are number of clock ticks (by default 100 ns) for output value 1 and 0.

Lowest possible frequency is cca 5 Hz:
* maximum value for write_pulses is 32767
* source clock frequency is 80 MHz
* maximum frequency divider is 255 => minimal clock frequency 314 kHz
=> one pulse time is 0.1 s at most
=> whole 1:1 period is 0.2 s = 5 Hz

By: Dušan

Dušan — Fri, 18 Dec 2020 14:39:57 +0000

In reply to Sara Santos.

I have tested completely all GPIOs. It seems like MicroPython (my version esp32-idf4-20200902-v1.13.bin) on ESP32 is using just 8 PWM channels (on 9th says: “out of PWM channels”), but sharing just one timer for all of them. Or maybe I am doing something wrong? You can try this:

from machine import Pin, PWM
from time import sleep

def TestPWM(pins):
pwm = []
print(“Setting PWM:”)
for pin in pins:
print(“*”, pin, end = “: “)
pwm.append(PWM(Pin(pin), freq = pin, duty = 500 + pin))
sleep(0.5)
print(pwm[-1])

print("After that:") for p in pwm: print("*", p)


print("Frequencies:")

for i in range(len(pwm)):

    pwm[i].freq(10 + i)

    print("* setting one to", 10 + i, end = ": ")

    for p in pwm:

        print(p.freq(), end = " ")

    print()

for p in pwm: p.deinit()

TestPWM((2, 3, 4, 5, 12, 13, 14, 15))
TestPWM((14, 15, 16, 17, 18, 19, 21, 22))
TestPWM((21, 22, 23, 25, 26, 27, 32, 33))
print(“OK”)

By: Sara Santos

Sara Santos — Thu, 17 Dec 2020 11:14:56 +0000

In reply to Dušan.

Hi.
Can you try using different GPIOs?
Regards,
Sara

By: Dušan

Dušan — Wed, 16 Dec 2020 21:05:30 +0000

Hello, I have some trouble with multiple PWM frequencies:
from machine import PWM, Pin
ledR = PWM(Pin(13), freq = 5000, duty = 200)
ledY = PWM(Pin(12), freq = 5000, duty = 200)
ledG = PWM(Pin(14), freq = 5000, duty = 200)
ledB = PWM(Pin(2), freq = 5, duty = 50)

Last line is setting frequency for all the LEDs. It seems like they share the same frequency. Is there a way to solve it?