Temperature Sensor drawing High Current

[spider]

Hello,

I have a problem with my electronics project.

Parts:

• "Arduino" Nano
• BME280 on PCB

Datasheet: https://www.bosch-sensortec.com/bst/products/all_products/bme280

Here is an image of the PCB because I don't have a schematic.
(Pin order: SDO; CSB; SCL; SDA; GND; VCC)

The sensor is directly connected to the Arduino via i2c and powered by the Arduino with 5v.

• 5V --> VCC
• GND --> GND
• A5 --> SCL
• A4 --> SDA

I am using this library to control the sensor:
https://github.com/adafruit/Adafruit_BME280_Library


According to the datasheet it should draw max. 0.3 µA in sleep mode.

Yet I am measuring these currents and voltages:

• VCC 420 µA
• GND -40 µA
• SCL -194 µA
• SDA -201 µA

• Reference is the VCC pin
• GND -4.7 v
• SCL -3.79 v
• SDA -3,76 v

The high current flow is particularly bad because it is probably generating a lot of heat within the temperature sensor.
I have no idea what is causing the high current flow. To me it looks like that there is too much current flowing over the data lines.

[floobydust]

BME280 is not a 5V part    It runs off 1.7-3.6VDC so you probably damaged it.
VCC should connect to +3.3V on the Arduino PCB.

[spider]

Changed it back to 3.3v. Sensor ist still working fine.
At 3.3v I can break the GND connection and it is still working.

I'll measure current and voltages tomorrow.

[floobydust]

It looks like your PCB does not have a I2C level-translator (3.3-5V), instead only using 4k7 resistors. Most BME280 boards have IC/MOSFETS for this.
So -ve currents will flow when 5V TX happens feeding into 3.3V part with 4k7.

The sensor has many modes and you can change the sample rate, filtering to lower current drain.

I found the Adafruit BME280 Arduino library gave high temperature readings. Several degrees C higher than should be read 
It might have a bug reading the calibration table for temperature. Tried another library and it was better. Bosch's C code is heavy on floating point for an Arduino.
Let me know how your temperature readings are.

The BME280 is sensitive to light, no bright light while reading it.

[spider]

I am sampling the sensor quite slow at 0.5 Hz and 16x oversampling for temperature and pressure.
It is reading 0.5°C higher than my ±0.5°C reference thermometer at 5v. On the other hand it is reading ±0.1°C at 3v compared to the reference thermometer.

At 3v I am now measuring these currents in sleep mode.

• VCC -40 µA
• GND 0 µA
• SCL 20 µA
• SDA 20 µA

-40 µA and 0 µA looks weird to me. While the sensor is reading the VCC current turns positive and the data lines negative. GND stays zero.