Part

Pressure, humidity and temperature, BME280

Temperature, humidity and air pressure as raw counts, and the datasheet sums that turn them into weather.

4 pins
4 settings
In 3 projects
In 1 lesson

Drawn live by the editor's own code, at the size you see it.

At a glance

The Pressure, humidity and temperature, BME280 in brief

What it is, and every setting the properties panel gives it.

The BME280 is Bosch’s pressure, humidity and temperature sensor, almost always bought on the purple GY-BME280 breakout with four pins: VIN, GND, SCL and SDA. The module has its own regulator and pull-ups, so VIN takes 3.3 or 5 V; on an Uno SDA and SCL go to A4 and A5, and on an ESP32 DevKit to GPIO 21 and 22. Its address is 0x76 on most purple boards, which is the part’s default, or 0x77 with the strap, where Adafruit’s library looks first. Mokxi models the register map from the datasheet: chip id 0x60 at 0xD0, raw twenty-bit counts plus the factory calibration a driver has to apply, sleep at power-up, forced and normal modes, measurement times from 8 ms at 1x oversampling to 113 ms at 16x, and the IIR filter. The temperature, pressure and humidity sliders are worked backwards into counts, so a correct driver reads them back. The classic mistake is begin() failing at the wrong address; in a hand-written driver it is humidity set in ctrl_hum, which only takes effect at the next ctrl_meas write. Noise, SPI mode and the humidity sensor’s slow response are not modeled.

Family: Sensors
Pins: 4
address: 118
temperature: 22
pressure: 1013.25
humidity: 50

Pins

4 pins

Named as the editor names them, so a wire lands where you expect it.

What it does

VIN

Supply. The module has its own regulator, so 3.3 V or 5 V.

GND

Ground.

SCL

I2C clock. The module carries the pull-ups.

SDA

I2C data.

How to use it

How to use the BME280 with an Arduino or ESP32

Four wires: VIN to 3.3 V or 5 V, GND to GND, and SDA and SCL to the board’s I2C pins. The project here runs on an ESP32-C3, whose I2C pins are GPIO 8 for SDA and GPIO 9 for SCL, and puts a BME280 at 0x76 and a BMP280 at 0x77 on the same two wires: the address strap is what lets them share. The chip id at 0xD0 tells them apart, 0x60 for the BME280 and 0x58 for the BMP280.

With Adafruit_BME280, give begin() the address. Most purple boards are at 0x76 and the library looks at 0x77 unless told, so a bare begin() fails on them; it also fails on a BMP280, which has no humidity. The project instead runs the datasheet’s integer formulas itself, temperature first, because pressure and humidity both need its t_fine. Drag a pressure slider and the altitude moves about 100 m for every 12 hPa.

Part pin

Board pin

VIN

3.3 V (3V3)

GND

SDA

GPIO 8

SCL

GPIO 9

On an Uno the module goes to A4 and A5 at 5 V, and on a classic ESP32 DevKit to GPIO 21 and 22; its regulator takes either supply.

ESP32-C3: two barometers on one buslive0.000 s 0.00x

Click to open it in the editor

This is the simulator itself, running here. Click anything to open it in the editor.

Open this project in the editor Read the full tutorial

The Adafruit library, at the purple board’s address

#include <Wire.h>
#include <Adafruit_BME280.h>
Adafruit_BME280 bme;
void setup() {
  Serial.begin(9600);
  if (!bme.begin(0x76)) {
    Serial.println("No BME280");
    while (1);
  }
}
void loop() {
  Serial.println(bme.readTemperature());
  Serial.println(bme.readPressure() / 100.0F);
  Serial.println(bme.readHumidity());
  delay(1000);
}

How it is modeled

What is true about the Pressure, humidity and temperature, BME280, here

In its help article’s own words: what the simulation gets right, and where it stops.

Modeled

The register map and the reset values: asleep at power-up, data registers at 0x80000 and 0x8000 until something is measured, im_update set for the 2 ms the chip spends copying its coefficients. Forced mode takes one measurement and goes back to sleep; normal mode measures, waits the standby time, and repeats. A measurement takes the datasheet's typical time, from 8 ms at 1x oversampling to 113 ms at 16x, with measuring set while it runs.

ctrl_hum only takes effect at the next write to ctrl_meas, and humidity oversampling left at 0 means no humidity at all: the register reads its reset value. Both are straight from the datasheet and both catch people.

Resolution follows oversampling, 16 bits at 1x up to 20 at 16x, and the IIR filter blends each result into the last, so a slider moved with the filter on is followed smoothly rather than in a jump.

Not modeled

Noise. A real reading wanders by a few pascals and a few hundredths of a degree, which is what oversampling and the filter are for; here more samples change only the time and the number of bits. The drivers use Bosch's 32-bit pressure formula, since the smaller boards have no 64-bit multiply, and it reads a few pascals off the 64-bit one. SPI mode, and so CSB and SDO as pins, are not modeled: this is the I2C module. The humidity sensor's slow response to a change in the air is not modeled.

From BME280 and BMP280 pressure sensors, in full.

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