BME280 | GUILCOR SENSORS

BME280
Temperature sensors

All-in-one environmental sensor measuring temperature, humidity, and pressure for IoT and weather monitoring systems.

Interface
I²C

Temperature range
-40 / 85°C

Humidity range (Rh)
0% → 100%

Pressure gauge (hPa)
300 → 1100

Temperature accuracy

+/- 0,5K

Humidity accuracy (rh)
+/- 3%

Pressure accuracy
+/- 1hPa

Internal resolution
20 bits

Power supply voltage
1,71 → 3,6V

Sampling rate
100Hz

Typical current
3,6µA (active)

Price
Medium

What is a BME280 sensor ?

The BME280 is an integrated environmental digital sensor designed by Bosch Sensortec.

It simultaneously measures temperature, humidity, and barometric pressure, providing a reliable estimate of altitude and local atmospheric conditions.

It is one of the most widely used sensors in IoT and weather applications, thanks to its small size, low power consumption, and stability over several years.

Operating principle

The BME280 integrates three sensors:

a MEMS pressure sensor (piezoresistive),
a capacitive humidity sensor,
and an integrated thermal sensor for compensation.

The raw data is digitized by a 20-bit ADC and then corrected using internal calibration coefficients stored in EEPROM.

Standard Bosch equations (simplified):

P = f(raw_p, raw_t)

T = f(raw_t)

RH = f(raw_h, T)

💡 The exact formulas are provided in the Bosch documentation and are based on 6 to 9 calibration coefficients.

Typical example of measurement

Parameter	Gross value (hex)	Calculated value
Temperature	0x6A90	24,8 °C
Humidity	0x5E20	46,5 % RH
Pressure	0x8A2C0	1013,2 hPa

🧮 Pressure can be converted into altitude:

Altitude (m) = 44330 × (1 − (P / 1013,25)^0,1903)

Principle diagram (I2C connection)

+3.3V
 │
[BME280]
 │ SDA ─────────┐
 │ SCL ─────────┤── [I²C Microcontroller]
 │ GND          │
 │ CSB / SDO ───┘ (config address or SPI)

💡 I²C Address: 0x76 if SDO=GND / 0x77 if SDO=VCC.

Application areas

🌤️ Connected weather stations and IoT

🚁 Drones (altimeter / air compensation)

⌚ Smartwatches and fitness trackers

🏠 Air conditioning and home automation systems

🧠 Industrial environmental monitoring

Should I choose a BME280 sensor ?

Strengths points

🌍 3 sensors in 1
→ Temperature, humidity, and pressure integrated into a single housing.
🎯 Stable and calibrated precision
→ Each sensor is individually calibrated by Bosch.
🔋 Very low consumption
→ Perfect for connected objects and wearable devices.
📡 Flexible interface (I²C or SPI)
→ Compatible with most MCUs and IoT platforms.

Weaknesses points

🌡️ Thermal sensitivity
→ The measurements can be influenced by the heat of the board if poorly insulated.
🧱 Unprotected case
→ No built-in hydrophobic filter — sensitive to condensation and dust.
📏 Complex calculations
→ The pressure/temperature/humidity conversions require the Bosch compensation equations.

Useful information

Here is some useful information regarding the BME280 sensors.

Main registers (I²C mode)

Address (hex)	Registry Name	Description
0xF2	ctrl_hum	Humidity configuration
0xF4	ctrl_meas	Temperature and pressure configuration
0xF5	config	Filtering and monitoring duration
0xF7 → 0xFE	Data registers	Raw data (p, T, RH)
0x88 → 0xA1	Calib data	Factory calibration coefficients

I²C Reading Example (simplified pseudo-code)

i2c_start();
i2c_write(0x76 << 1);
i2c_write(0xF7);
i2c_start();
i2c_write((0x76 << 1) | 1);
read 8 bytes -> raw_p[3], raw_t[3], raw_h[2];
i2c_stop();

temp = compensate_T(raw_t);
press = compensate_P(raw_p);
hum = compensate_H(raw_h);

💡 Compensation functions are provided by Bosch in the official libraries.

Typical integration diagram

3.3V ───────────┐ │ [BME280] │ SDA ───────┐ │ SCL ───────┤── MCU (Arduino, STM32, ESP32…) │ CSB/SDO ───┘ (I²C/SPI) │ GND

💡 Provide pull-up resistors of 4.7 kΩ on SDA and SCL if not present.

Excerpt from the configuration registers

Register	Bits	Function
ctrl_meas	[7:5] osrs_t / [4:2] osrs_p / [1:0] mode	Temperature, pressure, and mode configuration
config	[7:5] t_sb / [4:2] filter / [0] spi3w_en	Standby time, filtering, 3-wire SPI
ctrl_hum	[2:0] osrs_h	Humidity oversampling