ESP32 Confusing behaviour of PWM after soft reset
Consider:
from machine import Pin, PWM
pin = Pin(23, Pin.OUT)
pwm = PWM(pin, freq=38000, duty=338)
This works as expected. If you issue ctrl-d the waveform on the pin continues unchanged. If you paste the above code again, you cause a low output with
pwm.duty(0)
Subsequently changing the duty value to a value > 0 has no effect. This is surprising.
There is a simple workround of issuing pwm.deinit() at the start. The current state could be confusing to newcomers. It should either be documented or changed so that a soft reset de-initialises any PWM instance.
RP2: PWM duty cycle does not remain constant when frequency is changed
The expected behaviour is that if a duty cycle value is set, this should remain constant when the frequency is varied.
In the example code (used to drive a buzzer), the duty cycle starts at 50%, but as the frrequency is increased, the duty cycle increases up to 100%. This means that the buzzer stops sounding correctly as there is no longer any PWM occurring.
import machine
PWMOutput = machine.PWM(machine.Pin(0))
PWMOutput.duty_u16(32767)
freq = 500
while True:
for freq in range (120, 5000, 50):
PWMOutput.freq(freq)
for freq in range(5000, 120, -50):
PWMOutput.freq(freq)
To get round this, the cycle needs to be set ever time the frequency is set. Although this works, it does not seem the right way to be doing it.