8000 slow_pwm output can toggle more often than specified period · Issue #6545 · esphome/issues · GitHub
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slow_pwm output can toggle more often than specified period #6545

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pdw-mb opened this issue Dec 13, 2024 · 2 comments
Open

slow_pwm output can toggle more often than specified period #6545

pdw-mb opened this issue Dec 13, 2024 · 2 comments
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@pdw-mb
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pdw-mb commented Dec 13, 2024

The problem

Slow PWM recalculates its duty cycle every loop. This means that if the input changes mid-cycle, the output can change.

If you have an input that updates much more often than the slow PWM period, and the input is a bit noisy, the output can toggle several times each period in response to input changes.

In my case, I had a PID input that was updating every 5s and a PWM period of 5 minutes. When the system was in steady state, I would frequently get the output switching a few times on each PWM cycle due to noise on the temperature sensor. I do already have some smoothing on the PID output, but it seems that this isn't sufficient.

Obviously this should be easy to address with a filter on the sensor, and on reflection, I think the current behaviour is potentially useful, as it allows the system to respond quickly to big changes (such as turning the heating on and off), but it wasn't obvious to me from the documentation.

In fact, the documentation for the sigma delta output seems to suggest that it won't do this:

Unlike with Slow PWM Output, it is possible to update the output value with each update cycle, not just at the end of a longer period.

Perhaps the documentation for Slow PWM could be expanded with an additional note saying something like:

Note

The duty cycle will be recalculated whenever the input changes, and the output will be updated to reflect that. This can lead to the output toggling more than once per period particularly if the input is noisy, and has an update interval much shorter than the PWM period. It may be necessary to reduce the input period, or use filters to rate limit and/or smooth the input on order to avoid unwanted toggling of the output.

Which version of ESPHome has the issue?

2024.6.3

What type of installation are you using?

Home Assistant Add-on

Which version of Home Assistant has the issue?

2023.11.6

What platform are you using?

ESP32

Board

No response

Component causing the issue

No response

YAML Config

output:
  - platform: slow_pwm
    pin: GPIO26
    id: "heater_pwm"
    period: 300s

sensor:
  # Shelly add-on, uses duty-cycle to perform ADC input
  - platform: duty_cycle
    pin: 3
    id: add_on_adc
    name: "Add-on ADC"
    update_interval: 5s
    unit_of_measurement: "V"
    filters:
      - offset: -2.0
      - multiply: 0.033

  - platform: resistance
    id: resistance_sensor
    sensor: add_on_adc
    configuration: DOWNSTREAM
    resistor: 10kOhm
    name: Resistance Sensor

  - platform: ntc
    sensor: resistance_sensor
    calibration:
      - 11.4kOhm -> 26.6°C
      - 13.17kOhm -> 24°C
      - 16.17kOhm -> 18.8°C
    name: Floor Temperature
    id: floor_temperature

climate:
  - platform: pid
    id: pid_climate
    name: "Floor temperature"
    sensor: floor_temperature
    default_target_temperature: 16°C
    heat_output: heater_pwm
    control_parameters:
      kp: 1.04410
      ki: 0.00194
      kd: 140.43016
      output_averaging_samples: 5      # smooth the output over 5 samples
      derivative_averaging_samples: 10  # smooth the derivative value over 10 samples
    deadband_parameters:
      threshold_high: 0.5°C       # deadband within +/-0.5°C of target_temperature
      threshold_low: -0.5°C

Anything in the logs that might be useful for us?

No response

Additional information

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

@github-actions github-actions bot added the stale label Apr 13, 2025
@lutorm
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lutorm commented May 10, 2025

I agree this seems undesired. I would expect a PWM to change at most twice per period.

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