Enable CO2 auto calibration by default with toggle to disable

[bharvey88]

Version: 26.6.10.1

What does this implement/fix?

Enables the SCD40's automatic self-calibration (ASC) by default and adds a "CO2 Auto Calibration" switch so users can turn it off.

• With ASC on (the new default, matching the ESPHome default), the sensor corrects its own baseline as long as it sees fresh air (about 420 ppm) at least once a week. The manual 420 ppm recalibration every 1-2 years is no longer needed for most homes.
• The new switch is visible under Configuration, defaults to on, and persists across reboots and updates. Toggling takes effect immediately: the script stops periodic measurement, sends the ASC command over I2C (using the scd4x component's public write_command), and restarts measurement, the same sequence the component uses for forced calibration. The saved choice is re-applied ~20 seconds after every boot, since the SCD40 loses the setting on power loss and ESPHome re-applies the YAML default during setup.
• The "Calibrate SCD40 To 420ppm" button and the calibrate_co2_value action are unchanged and keep working whether ASC is on or off.
• Version bumped to 26.6.10.1.

Why a breaking change: existing devices get ASC turned on when they update. Readings may shift over the first days as the baseline self-corrects. Users whose device sits in a space that rarely gets fresh air (a sealed office, a basement, a grow room) should turn the new switch off and keep calibrating manually. Suggest including this in the release notes.

The same change is rolling out to AIR-1 and MSR-2 (identical), and R_PRO-1 (toggle fix/rename; its ASC was already on by default). A wiki update covering all four products is ready to merge alongside the firmware releases.

Verification: esphome compile passes for MTR-1.yaml, MTR-1_BLE.yaml, and MTR-1_Factory.yaml (ESPHome 2026.1.3). Not yet tested on hardware.

Types of changes

• Bugfix (fixed change that fixes an issue)
• New feature (thanks!)
• Breaking change (repair/feature that breaks existing functionality)
• Dependency Update - Does not publish
• Other - Does not publish
• Website of github readme file update - Does not publish
• Github workflows - Does not publish

Checklist / Checklijst:

• The code change has been tested and works locally
• The code change has not yet been tested

If user-visible functionality or configuration variables are added/modified:

• Added/updated documentation for the web page

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📥 Commits

Reviewing files that changed from the base of the PR and between c651431 and 930aaba.

📒 Files selected for processing (1)

• Integrations/ESPHome/Core.yaml

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