Calibration Guide

Calibrating UltimateSensor Mini v2 improves presence detection, zone tracking and environmental readings. The Mini v2 uses both HLK-LD2412 and HLK-LD2450 mmWave radar modules on standard hardware, plus SCD41, SGP41, BH1750 and optional SPS30 sensors. If the optional HLK-LD2460 upgrade is installed, it replaces the LD2450 module.

Mini v2 has no barometric pressure sensor, no microphone, no speaker and no PIR sensor.

What You Can Calibrate

mmWave Radar Tuning

Mini v2 combines two radar modules:

• LD2412 is best for reliable room occupancy and still presence.
• LD2450 is best for zones, target position and multi-target tracking on standard hardware.
• LD2460 is an optional tracking upgrade that replaces LD2450 and uses target 1-5 X/Y/Distance/Angle entities plus shared Room Designer polygon zones.

Tune LD2412 first. After room occupancy is stable, tune LD2450 zones or follow the LD2460 Upgrade Guide for physical orientation, mounting compensation, the hardware detection sector and Room Designer zones.

LD2412 Background Calibration

Run this when the room shows occupied while nobody is there.

1. Make the room completely empty.
2. Remove pets and stop moving objects such as fans, curtains or robot vacuums.
3. Open Home Assistant.
4. Go to Settings -> Devices & services -> ESPHome.
5. Open your UltimateSensor Mini v2.
6. Enable the button LD2412 Dynamic Background Correction if you have not done so yet. It is disabled by default; you find it under the disabled entities of the device.
7. Press LD2412 Dynamic Background Correction.
8. Wait until the diagnostic entity with the same name has turned off before entering the room again.

Important: if someone is in the room during background correction, the radar can learn that person as part of the background.

LD2412 Distance Gates

The LD2412 uses distance gates. Each gate represents a distance segment. With the common 0.75 m resolution:

Set LD2412 Maximum Distance Gate to match the room. If the sensor detects through a wall, lower the maximum gate.

LD2412 Timeout and Energy

The standard firmware does not expose per-gate thresholds. Tune with the distance gates, and check the energy values with the room empty.

LD2450 Zone Tuning

The LD2450 tracks targets in X/Y coordinates. Use it for desk zones, couch zones or ignoring a doorway.

If your Mini v2 has the optional LD2460 upgrade, skip the native LD2450 zone controls and use the LD2460 Upgrade Guide. LD2460 physically replaces LD2450 and requires matching *-ld2460.yaml firmware.

Coordinate System

        Sensor (0,0)
           |
    -X <---+---> +X
           |
           v
       +Y distance

Zone Example

For a 3 m wide by 4 m deep area:

Values are usually in millimeters. If you see targets outside the room, tighten the Tracking Zone 1 X1/Y1/X2/Y2 boundaries and lower the LD2412 Maximum Distance Gate for the real room size.

Common Radar Problems

CO2 Calibration

Mini v2 uses the Sensirion SCD41 for CO2, temperature and humidity. Automatic self-calibration is on; it works best when the room is aired well now and then. Use the steps below when readings stay off.

Manual Fresh-Air Calibration

1. Ventilate the room well for at least 3 minutes, or place the sensor in fresh outdoor air within WiFi range.
2. Wait until the reading is stable.
3. In Home Assistant, open the Mini v2 device.
4. Press CO2 Manual Calibration. This button is disabled by default, so enable it first. It sets the sensor to 420 ppm.
5. Verify that fresh-air readings settle around 400-430 ppm.

Do not calibrate in a room with people present or poor ventilation.

CO2 Reference

Temperature and Humidity

Temperature and humidity can be affected by enclosure heat, sunlight, nearby electronics or poor airflow. Mini v2 firmware has two correction layers:

The current Mini v2 firmware uses the SCD41 temperature_offset setting for the main self-heating compensation. This is the preferred place for permanent temperature correction because the SCD41 also uses this value internally when compensating humidity.

The default Mini v2 value is below. The SCD41 subtracts this value from its reading, so a higher value gives a lower temperature.

substitutions:
  scd41_temperature_offset: "10.2"

Home Assistant also exposes these configuration entities on the device page:

• Temperature Offset - adds a small correction to the displayed SCD41 Temperature.
• Humidity Offset - adds a small correction to the displayed SCD41 Humidity.

These Home Assistant offsets are stored on the device and restored after reboot. They are useful for quick testing or small site-specific corrections, but for a permanent setup we recommend putting the final temperature correction in the ESPHome substitution and reflashing. This keeps the firmware self-contained and avoids hidden corrections that are easy to forget later.

Recommended Workflow

1. Update to the current Mini v2 firmware.
2. Keep Temperature Offset and Humidity Offset in Home Assistant at 0.
3. Place a reliable thermometer/hygrometer near the sensor.
4. Wait at least 20-30 minutes for both readings to stabilize.
5. Compare the reference values with SCD41 Temperature and SCD41 Humidity.
6. If temperature is structurally off, follow the ESPHome customization steps, adjust scd41_temperature_offset, and reflash.
7. After temperature is correct, only use Humidity Offset if humidity still needs a small final correction.

Temperature Substitution Examples

If SCD41 Temperature reads 1.0 °C too high, raise the substitution by 1.0:

substitutions:
  scd41_temperature_offset: "11.2" # default 10.2 + 1.0

If SCD41 Temperature reads 0.8 °C too low, lower the substitution by 0.8:

substitutions:
  scd41_temperature_offset: "9.4" # default 10.2 - 0.8

Do not correct the same temperature error twice. If you change scd41_temperature_offset, reset the Home Assistant Temperature Offset back to 0.

Home Assistant Fine Tuning

Use the Home Assistant offsets when you want to test quickly or cannot reflash immediately:

1. Open the Mini v2 device in Home Assistant.
2. Find Temperature Offset or Humidity Offset under the configuration entities.
3. Enter the correction you want to add to the displayed reading.

Examples:

• Sensor reads 24.5 °C, reference is 23.8 °C: set Temperature Offset to -0.7, or preferably raise scd41_temperature_offset by 0.7 and keep the HA offset at 0.
• Sensor reads 48% RH, reference is 52% RH: set Humidity Offset to 4.

For humidity, first make sure temperature is correct. Relative humidity is temperature-dependent, so a wrong temperature correction can also make humidity look wrong.

If you are not familiar with ESPHome YAML yet, use the Home Assistant offsets first. When you want to make the correction permanent, follow the Firmware Guide to adopt the Mini v2, edit the substitution and upload the firmware again.

VOC and NOx

The SGP41 reports VOC and NOx index values. These are relative air-quality indexes, not direct ppm values. After flashing or moving the sensor, allow several hours of normal operation before judging the readings.

Light Sensor

The BH1750 lux sensor is factory calibrated. If you need an exact match with another lux meter, adopt the device in ESPHome and apply a correction filter to the illuminance sensor.

Optional SPS30

If your Mini v2 has the SPS30 module, compare PM readings with a trusted reference device only after the sensor has warmed up and has stable airflow around the housing.

Best Practices

• Tune radar with the room empty first.
• Limit radar range to the actual room size.
• With LD2460 upgrade firmware, tune physical placement, the hardware detection sector and shared Room Designer polygon or exclusion zones.
• Avoid direct sunlight, radiators and strong airflow.
• Recalibrate CO2 after moving the sensor.
• Keep notes of changed settings and offsets.

Related

• Sensor Definitions
• Usage Guide
• Troubleshooting
• Firmware Guide