1. Group 7 Natalia M., Matt Y., David K., Zac L.
BME680: Pressure
Group 7
Natalia M., Matt Y., David K., Zac L.

2. BME680 – General facts What is it? An environmental sensor
Can measure temperature, pressure, relative humidity, and air quality through the detection of organic compounds
Designed for mobile applications, wearables, home weather stations
Has a low power consumption

3. How it works Uses an Absolute Barometric Pressure Sensor
Absolute  Require a reference point
Reference point: pressure relative to a perfect vacuum
(Basically this but better)
Freshman Physics Flashback 😱

4. Barometric Pressure Sensors (in general)
Measure pressure changes exerted by the atmosphere
Uses the Ideal Gas Law: PV=nRT and F=mg=pgV=pghS
From these equations, a differential equation can be obtained and solved to get a barometric formula:
THIS IS JUST AN ESTIMATE

5. Composition/Features
Vacuum reference chamber is sealed on one side of integrated circuit
Polysilicon used for hermetic seal
Pressure pushes on plate which rests on piezoresistive elements, sending a signal proportional to pressure
Offset voltage is voltage output when perfect vacuum is applied
Offset voltage used to get proper calibration
Span is full scale output minus the offset voltage

6. Measurement Range & Accuracy
BME 680 can measure from 300 to 1100 hPa with 1hPa accuracy
Pressure sensor has 0.25% sensitivity error
Temperature coefficient offset of 1.3 Pa/K
RMS Noise: 0.12 Pa
RMS Noise is the noise of an electronic system or the sound pressure level relative to its reference value
The square root of the average of the square of the pressure of the sound signal over a given time
The BME680 allows for oversampling to help lower noise
Can enable IIR (Infinite Impulse Response) filter to increase resolution from 16 to 20 bit
(1 hPa [hecto-Pascal) = 100 Pa)

7. IIR Filter in the BME680 20 bit resolution
Data from current filter memory
New value of filter memory
Data from current ADC aquisition
20 bit resolution
Helps suppress disturbances (ex. such as wind blowing into the sensor)
Response time with IIR filter depends on the filter coefficient used. We probably won’t be using IIR filters because of this
Can be applied to both temperature as well as pressure, but not for any other data
Temperature and pressure get updated together

8. References