Arduino BME280: MEMS sensing explained clearly

Video Tutorial (Optional)

Watch first if you want the high-level walkthrough of how the BME280 measures pressure, humidity, and temperature.

Project Overview

Arduino or Raspberry Pi + BME280: This overview explains (at a high level) how the BME280 MEMS sensor converts environmental pressure, humidity, and temperature into values you can read on your computer.

The BME280 (by Bosch) is a popular sensor for DIY projects because it measures pressure, humidity, and temperature accurately, and it can even be used as an altimeter after proper calibration.

Note that Bosch does not disclose all internal operating mechanisms due to intellectual property reasons, so some details are inferred.

Time: 10 to 20 minutes
Skill level: Beginner
What you will build: A practical understanding of the pressure, humidity, and temperature sensing principles inside the BME280

Parts List

From ShillehTek

No parts required for this MEMS overview

External

BME280 sensor module (Bosch) - the MEMS sensor discussed in this post

Note: This post focuses on how the BME280 works internally, not on wiring or programming it on a specific board.

Step-by-Step Guide

Step 1 - Understand what the BME280 measures

Goal: Know what signals the BME280 provides and why it is useful in Arduino and Raspberry Pi projects.

What to do: The BME280 measures pressure, humidity, and temperature. With calibration, pressure readings can also be used to estimate altitude.

Expected result: You know which environmental properties the BME280 converts into digital readings.

Step 2 - Pressure sensing (piezoresistive Wheatstone bridge)

Goal: Understand the high-level mechanism used for pressure measurement.

What to do: Bosch describes the main pressure mechanism as a piezoresistive Wheatstone bridge on top of a flexible membrane. Membrane distortion changes the bridge output voltage, which can be measured and correlated to pressure (given known system properties).

The Bosch community discussion referenced in the original post is here.

A Wheatstone bridge is an electrical circuit used to measure unknown resistance. It uses four resistive elements arranged in a diamond-like configuration, and it is simple enough to be practical in micro-level electronics such as the BME280.

Expected result: You understand why membrane deformation can be converted into a measurable electrical signal using a Wheatstone bridge.

Step 3 - Humidity sensing (capacitive humidity technology)

Goal: Understand the commonly cited humidity sensing principle used in MEMS humidity sensors.

What to do: It is speculated that the BME280 uses “capacitive humidity technology.” At a high level, humidity changes the capacitance of a material between two electrodes. As more water molecules lodge into porous sections of the material, capacitance changes. The sensor measures this change and maps it to a humidity level. A heating element is used to improve response time.

Diagram screenshot illustrating capacitive humidity sensing concept used in MEMS humidity sensors

Illustration of porous dielectric material between electrodes changing capacitance as humidity increases — **Source:** https://www.intechopen.com/chapters/77296

The layer thickness, pore size, and other physical details for this specific sensor are not publicly known. The actual implementation could differ, but pore-based capacitive sensing is common in MEMS.

Expected result: You understand how changing moisture content can be turned into a measurable capacitance signal.

Step 4 - Temperature sensing (diode-based measurement)

Goal: Understand how a diode can be used to measure temperature in an IC.

What to do: Bosch indicates the BME280 uses a diode mechanism for temperature measurement. A diode is a two-terminal component that allows current to flow in one direction and blocks it in the other direction.

Diode orientation diagram showing forward-bias and reverse-bias current flow

Diode circuit diagram example used to explain diode behavior for temperature sensing — **Source:** https://www.build-electronic-circuits.com/what-is-a-diode/

When a diode is subject to a temperature change, its forward voltage drops. By measuring the diode voltage and using known system properties, that voltage change can be extrapolated to a temperature reading. Resistors are used to create a stable current, which is essential for accurate measurements.

Example circuit showing how diode forward voltage varies with temperature for sensing — **Source:** https://www.openimpulse.com/blog/2012/07/low-cost-diode-temperature-sensor/

Expected result: You understand why monitoring diode forward voltage can provide a temperature reading.

Step 5 - Follow and support (optional)

Goal: Keep up with future sensor and electronics content.

What to do: Subscribe on Youtube and support the content here: https://www.buymeacoffee.com/mmshilleh.

Expected result: You have the original creator links saved for future posts.

Conclusion

You now have a high-level understanding of how the BME280 retrieves pressure, humidity, and temperature values using MEMS-scale mechanisms, including a piezoresistive Wheatstone bridge, capacitive humidity sensing, and diode-based temperature measurement.

Want parts for your next sensor build? Grab what you need from ShillehTek.com. If you want help selecting sensors, designing your electronics, or turning a prototype into a product, check out our IoT consulting services.