Arduino Uno BMP280 Simulator: Wiring, Code and a Live Circuit
This is a BMP280 barometric pressure and temperature sensor wired to an Arduino Uno over I2C, read live with the Adafruit BMP280 library: temperature, pressure and altitude once a second.
Four wires: 3.3 V, GND, SDA to pin A4 and SCL to pin A5. In the editor, drag the sensor’s pressure slider and the altitude moves with it.
- 5 V logic
- Library: Adafruit_BMP280.h
- I2C address 0x76
- SDA A4, SCL A5
Wiring the BMP280 to the Arduino Uno
Every connection in the circuit above, with the board’s own pin names.
| BMP280 pin | Arduino Uno pin | Why |
|---|---|---|
| VIN | 3.3V | The BMP280 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. |
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 BMP280 breakout has no regulator, so it runs from the Arduino Uno’s 3.3V pin, not 5V. Its I2C pull-ups then go to 3.3 V, which the ATmega328P reads as high.
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 BMP280 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
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_BMP280.h>
Adafruit_BMP280 bmp; // on I2C: SDA pin A4, SCL pin A5
void setup() {
Serial.begin(9600);
if (!bmp.begin(0x76)) {
Serial.println("No BMP280 at 0x76");
for (;;) {}
}
Serial.println("BMP280 found");
}
void loop() {
Serial.print("Temperature: ");
Serial.print(bmp.readTemperature(), 1);
Serial.print(" C Pressure: ");
Serial.print(bmp.readPressure() / 100.0F, 1);
Serial.print(" hPa Altitude: ");
Serial.print(bmp.readAltitude(1013.25), 0);
Serial.println(" m");
delay(1000);
}
bmp.begin(0x76) reads the chip’s ID and its factory calibration, which every reading needs. It returns false when nothing answers at that address; boards with SDO tied high answer at 0x77 instead.
readTemperature() is degrees Celsius and readPressure() is pascals, so dividing by 100 gives hectopascals, the unit weather reports use. readAltitude(1013.25) turns pressure into meters above the level where it would be 1013.25 hPa; give it your local sea-level pressure for a true altitude.
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 BMP280 on the Arduino Uno
The wrong address
Adafruit’s own board answers at 0x77, the cheap purple ones at 0x76, and bmp.begin() with no argument tries 0x77. If it fails, try the other address before suspecting the wiring.
Powering a bare breakout from 5V
The six-pin purple board has no regulator, so 5V goes straight to a chip rated for 3.6 V. Use the Arduino Uno’s 3.3V pin, as in the circuit above.
Confusing it with a BME280
The BME280 looks the same and adds humidity. A BMP280 reports a chip ID of 0x58, a BME280 0x60, and each library refuses the other. If begin() fails at both addresses, check which chip you have.
Questions and answers
Can I simulate a BMP280 with an Arduino Uno?
Yes. The circuit at the top of this page is an Arduino Uno with a BMP280, running in your browser on a simulated ATmega328P. The temperature 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 BMP280 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.
How accurate is the altitude?
Pressure changes with the weather by more than it changes over a few floors, so readAltitude() is only as good as the sea-level pressure you give it. Relative changes over a few minutes are accurate to about a meter.
Can I use the BMP280 over SPI?
The chip supports SPI, but this simulated part speaks I2C. Most breakouts are wired for I2C out of the box anyway.
Build your own BMP280 project
Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.