Arduino Uno BME280 Simulator: Wiring, Code and a Live Circuit
This is a BME280 temperature, humidity and pressure sensor wired to an Arduino Uno over I2C, read live with the Adafruit BME280 library once a second.
- 5 V logic
- Library: Adafruit_BME280.h
- I2C address 0x76
- SDA A4, SCL A5
Wiring the BME280 to the Arduino Uno
Four wires: 3.3 V, GND, SDA to pin A4 and SCL to pin A5. In the editor, drag the sensor’s temperature, humidity and pressure sliders and the next reading follows.
Every connection in the circuit above, with the board’s own pin names.
| BME280 pin | Arduino Uno pin | Why |
|---|---|---|
| VIN | 3.3V | The BME280 chip is a 3.3 V part; many breakouts have no regulator. |
| GND | GND | Common ground. |
| SCL | pin A5 | I2C clock. |
| SDA | pin A4 | I2C data. |
Power
On an Uno the I2C bus is A4 (SDA) and A5 (SCL). The SDA and SCL pins beside AREF are the same two wires, so either pair works. The common purple BME280 breakout has no regulator, so it runs from the Arduino Uno’s 3.3V pin, not 5V.
Pins to leave alone on the Arduino Uno
Pins 0 and 1 are the USB serial port on a real Uno, so anything wired there fights the upload and the serial monitor. Pin 13 carries the onboard LED.
On a real bench
On a real bench the Uno stands beside the breadboard: the BME280 goes into the breadboard and male-to-male jumpers run from the Uno’s female headers to its rows. Power the Uno from USB while you build, and unplug it before you move a wire.
The code, and what it does.
The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
Adafruit_BME280 bme; // on I2C: SDA pin A4, SCL pin A5
void setup() {
Serial.begin(9600);
if (!bme.begin(0x76)) {
Serial.println("No BME280 at 0x76");
for (;;) {}
}
Serial.println("BME280 found");
}
void loop() {
Serial.print("Temperature: ");
Serial.print(bme.readTemperature(), 1);
Serial.print(" C Humidity: ");
Serial.print(bme.readHumidity(), 1);
Serial.print(" % Pressure: ");
Serial.print(bme.readPressure() / 100.0F, 1);
Serial.println(" hPa");
delay(1000);
}
bme.begin(0x76) reads the chip’s ID and its factory calibration. It returns false when nothing answers at that address. Adafruit’s own board is at 0x77 and begin() with no argument tries that one; most purple modules are at 0x76.
readTemperature() is degrees Celsius, readHumidity() is percent relative humidity and readPressure() is pascals, so dividing by 100 gives hectopascals. All three come from one chip, which is the difference from a BMP280: it adds the humidity.
Serial.begin(9600) opens the serial monitor. Serial goes over the USB cable, and the serial monitor in the editor reads it at whatever baud rate the sketch sets.
Common mistakes with the BME280 on the Arduino Uno
The wrong address
Adafruit’s board answers at 0x77, the cheap purple ones at 0x76, and bme.begin() with no argument tries 0x77. If it fails, try the other address before suspecting the wiring.
Using a BMP280 library
A BMP280 has no humidity and a different chip ID (0x58 against 0x60). Adafruit_BMP280 refuses a BME280 and the reverse, so match the library to the chip printed on the module.
Powering a bare breakout from 5V
A module with no regulator sends 5V straight to a chip rated for 3.6 V. Use the Arduino Uno’s 3.3V pin, as in the circuit above.
Questions and answers
Can I simulate a BME280 with an Arduino Uno?
Yes. The circuit at the top of this page is an Arduino Uno with a BME280, running in your browser on a simulated ATmega328P. The temperature, humidity and pressure sliders set what the simulated chip measures, and the library applies the real calibration math to it. Press Run it in the editor to change the wiring or the code; it is free and needs no account.
Where does the BME280 connect on the Arduino Uno?
On an Uno the I2C bus is A4 (SDA) and A5 (SCL). The SDA and SCL pins beside AREF are the same two wires, so either pair works.
What is the difference between the BME280 and the BMP280?
The BME280 adds a humidity sensor. The two use different libraries and report different chip IDs.
Why does it read a little warm?
On a real board the chip’s own heat and the board around it warm the sensor, so the temperature reads a degree or two high. The simulated chip reports exactly what its slider says.
Build your own BME280 project
Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.