[Bug] Device value less than 1% showing 100% in HomeKit

[jtheller]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have IKEA TRADFRI bulbs that could be dimmed all the way down to 1/254 reported value in Zigbee2mqtt, or 0.39%. For some reason when the percentage value goes less than 1 it will be mistakenly reported as 100% in the Home app...could be an Apple thing for them to fix, but in the meantime could we implement this to monitor.ts?-

transformValueFromMqtt(value: unknown): CharacteristicValue | undefined {

  ...

  const percentage = (input - this.input_min) / (this.input_max - this.input_min);

  const result = out_minimum + percentage * (out_maximum - out_minimum);

  // Limit min possible return value to 1.
  if (result < 1 && result > 0) return Math.ceil(result);

  return result;
}

This will help HomeKit read less than 1% values somewhat correctly.

I believe the change should only affect lights and battery percentages.

Related devices

• TRADFRI LED bulb E26/E27 800/806 lumen, dimmable, white spectrum, clear

and potentially other bulbs.

Related Devices

No response

Steps To Reproduce

1. Use hardware dimmer switch or remote, or through Zigbee2mqtt, dim the lights to a brightness percentage value of less than 1%.
2. Observe in the Home app that reported brightness stays or jumps back to 100%.
3. Raise the brightness to a percentage value of greater than or equal 1%.
4. Observe in the Home app that reported brightness resumes correctly again.

Expected behavior

Expect in the Home app that the reported value should correctly follow the calculated percentage even when it's less than 1%.

Device entry

No response

Status update

No response

Messages from this plugin

No response

This plugin

1.9.2

Homebridge

1.6.0

Zigbee2MQTT

1.30.3

Homebridge Config UI X (if applicable)

No response

[itavero]

Can you make a PR for this?
Never seen this behavior myself, but I'm happy to look and test a PR for this.

[jtheller]

Here is a short clip showing the problematic behavior, notice around 10s when the brightness value is 1 the percentage shown in Home app goes all the way to 100%.

Screen.Recording.2023-04-27.at.8.02.23.PM-1.mov

[stale]

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[burmistrzak]

Here is a short clip showing the problematic behavior, notice around 10s when the brightness value is 1 the percentage shown in Home app goes all the way to 100%.

I can confirm that's a UI/UX bug in the Home app, iOS 17.2 still being affected.
It's likely caused by the bulb being in a technically invalid state, i.e. powered on but simultaneously at 0% brightness.
Zero percent brightness is treated by HAP as powered off, and because 1/254 is approximately 0.39%, HomeKit will automatically round it down to 0%... 🙄