Sensor Module BME280

The CWX uses a BME280 High Precision Temperature, Humidity and Barometric Pressure Sensor.  This digital sensor module being contained on it's own PCB and interfaces to the standard I2C bus, such as used on most microcontrollers such as ESP8266 series, Arduino boards, Raspberry PI etc.

This BME280 module is factory calibrated to provide a high accuracy reliable, stable and durable sensor for many microelectronic projects.

• Temperature Range -40 to +85°C (with ±1.0°C accuracy)
• Humidity Range 0-100% (with ±3% accuracy)
• Pressure Range 300-1100 hPa (with ±1 hPa absolute accuracy)
• Voltage Range 1.8 to 5V DC
• I2C speed, up to 3.4 MHz
• I2C Default Address 0x76 (can be changed by altering the S1 solder pads)

 

 

This module can be interfaced to either 5V or 3V3 (3.3v), electronic projects, the CWX-1 is 3V3 based.

These modules may be supplied configured as either 5V or 3V3, as shown in the below schematic.

 

 

Using either default voltage selection, the BME280 will still work on the CWX.

The fixed voltage regulator (U4), is a small LDO device and allows the BME280 to work from a supply voltage range of circa 1.8 - 5V DC.

 

Possible Performance Improvements

Removing the LDO (Cystek LM6206-3.0 SOT23 Device), has been reported to:

• Increase the battery life.
  • The LDO may have minuscule residue operating current and a valid point.
    • According to the datasheet, this device can draw up to 15uA, but typically only 7uA.
• Improve the temperature accuracy (due to potential heat from regulator)
  • This is very unlikely as the LDO is other side of PCB and opposite ends.

This involves carefully removing the 3pin LDO device and shorting pins as shown, which we have done in preparation for some future testing.  Photo shows the LDO in place and on the right, the LDO removed and a short added.

Note: This will require some fine soldering and ideally a magnifier of some description.

 

 

The current has been reported to drop from around 7uA to 0.2uA in sleep mode.   Looking at the LDO datasheet, this would seem reasonable.

The normal operating mode current has been reported to fluctuate around 700uA to 300uA.  The code is best written to keep the sensor in sleep mode as long as possible, during the loop cycle.

Both of these measurements are to be checked. Feedback welcomed.

 

External

Other external reading which may be of interest.