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[Bug]: LilyGo T-Beam V1.2 (SX1276/AXP2101) - BME280 sensor data corrupted (wrong temp ~52-65°C, humidity/pressure missing)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
c
Domain
embedded-iot

Research direction

Start by locating the BME280 driver and the LilyGo T-Beam V1.2 (SX1276) board initialization path, then trace the I2C startup and calibration register reads. Compare the reported temperature with the missing humidity and pressure values to identify where initialization or compensation data fails. Done means the sensor initializes reliably and reports plausible temperature, humidity, and pressure on this board.

Written by the indexing model from the issue text.

Description

[Bug]: LilyGo T-Beam V1.2 (SX1276/AXP2101) - BME280 sensor data corrupted (wrong temp ~52-65°C, humidity/pressure missing)
Description:
Hi developers,
I am facing an issue with an external BME280 sensor connected to a LilyGo T-Beam V1.2 (SX1276 with AXP2101 PMU) running the latest MeshCore firmware.
The exact same hardware setup was previously running flawlessly under Meshtastic, so a hardware or wiring defect can be 100% ruled out.
Hardware Setup:
• Board: LilyGo T-Beam V1.2 (SX1276 / AXP2101)
• Sensor: BME280 (3.3V version, 6-pin breakout board)
• Wiring:
• SDA connected to GPIO 21
• SCL connected to GPIO 22
• SDO hardwired to GND (forcing I2C address 0x76)
• CSB hardwired to 3V3 (forcing I2C mode)
• Peripherals: An OLED display is sharing the same I2C bus (Pins 21/22 and 3V3/GND) and works perfectly fine.
The Problem:
When using MeshCore (flashed via the official web flasher using the LilyGo T-Beam 1.2 (SX1276) target), the BME280 sensor fails to initialize properly:

  1. Temperature: The MeshCore App displays an absurdly high, incorrect temperature reading between 52°C and 65°C at normal room temperature.
  2. Humidity & Pressure: Both values are completely missing/not populated in the telemetry layout.
    Suspected Cause:
    It seems like a timing issue with the AXP2101 PMU during the boot sequence or a calculation error within the sensor driver's compensation registers. Because the OLED display initializes on the same rail, a minor voltage dip at startup might cause the BME280 to fail reading its internal calibration EPROM data, leading to corrupt raw data interpretation (which mathematically ends up as ~52-65°C).
    Could you please look into the I2C startup sequence or the BME280 calibration register readout for the T-Beam V1.2 target?
    Thank you for your amazing work on MeshCore!
Dominant language
C
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