BME280 with Arduino Uno — safe 3.3 V wiring and weather readings

The BME280 measures temperature, humidity and air pressure in one tiny chip, which makes it the usual sensor for a home weather station. It is more accurate than a DHT22 and reads in milliseconds instead of seconds.

The chip is 3.3 V-only, and most cheap purple 6-pin boards pass the pins straight through. On a 5 V Uno that means two things. Power it from the 3.3V pin, which can supply about 50 mA — far more than the sensor needs. And put a BSS138 level shifter on SDA and SCL, because the Uno’s Wire library pulls those lines up to 5 V.

The sketch prints the chip ID so you can tell a real BME280 from a BMP280. It then takes a forced-mode reading every 5 seconds.

Wiring

Board quirks

• Bosch rates the BME280 at 3.6 V maximum on every pin. On the Uno, the Wire library pulls SDA/SCL up to 5 V, so a direct connection overstresses a bare board. The level shifter fixes that.
• Boards with a VIN pin, a 3-pin regulator and two small transistors already shift levels — wire those to 5V and SDA/SCL directly and skip the shifter.
• Many “BME280” listings ship a BMP280 (no humidity). The sketch prints the chip ID: 0x60 = BME280, 0x58 = BMP280.
• Forced mode takes one reading every 5 s and sleeps in between, so the chip doesn’t heat itself and read high.

Code

// BME280 temperature + humidity + pressure on an Arduino Uno R3 (I2C).
// 3.3 V-only 6-pin board: VIN/VCC → 3.3V, SDA/SCL through a BSS138 level shifter,
// SDO → GND (0x76), CSB → 3.3V (I2C). Forced mode: one reading per request, then sleep,
// so the sensor doesn't warm itself up.
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

Adafruit_BME280 bme;

void setup() {
  Serial.begin(9600);
  if (!bme.begin(0x76) && !bme.begin(0x77)) {
    Serial.println(F("No BME280 at 0x76 or 0x77 - check 3.3V, the shifter and SDO"));
    for (;;) {}
  }
  Serial.print(F("BME280 found (chip ID 0x"));
  Serial.print(bme.sensorID(), HEX);
  Serial.println(F(")"));
  bme.setSampling(Adafruit_BME280::MODE_FORCED, Adafruit_BME280::SAMPLING_X1, Adafruit_BME280::SAMPLING_X1,
                  Adafruit_BME280::SAMPLING_X1, Adafruit_BME280::FILTER_OFF);
}

void loop() {
  bme.takeForcedMeasurement();
  Serial.print(F("Temp "));
  Serial.print(bme.readTemperature(), 1);
  Serial.print(F(" C  Humidity "));
  Serial.print(bme.readHumidity(), 1);
  Serial.print(F(" %  Pressure "));
  Serial.print(bme.readPressure() / 100.0, 1);
  Serial.println(F(" hPa"));
  delay(5000);
}

// BME280 temperature + humidity + pressure on an Arduino Uno R3 (I2C).
// 3.3 V-only 6-pin board: VIN/VCC → 3.3V, SDA/SCL through a BSS138 level shifter,
// SDO → GND (0x76), CSB → 3.3V (I2C). Forced mode: one reading per request, then sleep,
// so the sensor doesn't warm itself up.
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

Adafruit_BME280 bme;

void setup() {
  Serial.begin(9600);
  if (!bme.begin(0x76) && !bme.begin(0x77)) {
    Serial.println(F("No BME280 at 0x76 or 0x77 - check 3.3V, the shifter and SDO"));
    for (;;) {}
  }
  Serial.print(F("BME280 found (chip ID 0x"));
  Serial.print(bme.sensorID(), HEX);
  Serial.println(F(")"));
  bme.setSampling(Adafruit_BME280::MODE_FORCED, Adafruit_BME280::SAMPLING_X1, Adafruit_BME280::SAMPLING_X1,
                  Adafruit_BME280::SAMPLING_X1, Adafruit_BME280::FILTER_OFF);
}

void loop() {
  bme.takeForcedMeasurement();
  Serial.print(F("Temp "));
  Serial.print(bme.readTemperature(), 1);
  Serial.print(F(" C  Humidity "));
  Serial.print(bme.readHumidity(), 1);
  Serial.print(F(" %  Pressure "));
  Serial.print(bme.readPressure() / 100.0, 1);
  Serial.println(F(" hPa"));
  delay(5000);
}

Library: Adafruit BME280 Library (Adafruit (also install Adafruit Unified Sensor)) — compiled with Adafruit BME280 Library 2.3.0.

Expected serial output

BME280 found (chip ID 0x60)
Temp 27.8 C  Humidity 61.2 %  Pressure 1007.9 hPa
Temp 27.8 C  Humidity 61.4 %  Pressure 1007.9 hPa

BME280 found (chip ID 0x60)
Temp 27.8 C  Humidity 61.2 %  Pressure 1007.9 hPa
Temp 27.8 C  Humidity 61.4 %  Pressure 1007.9 hPa

Common errors