Arduino Uno R4 · BMP280

Arduino Uno R4 BMP280 Simulator: Wiring, Code and a Live Circuit

This is a BMP280 barometric pressure and temperature sensor wired to an Arduino Uno R4 Minima 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.

Run it in the editor Read the code

5 V logic
Library: Adafruit_BMP280.h
I2C address 0x76
SDA A4, SCL A5

Arduino Uno R4 · BMP280live0.000 s 0.00x

Click to open it in the editor

The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Wiring the BMP280 to the Arduino Uno R4

Every connection in the circuit above, with the board’s own pin names.

BMP280 pin	Arduino Uno R4 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.

The Uno R4 keeps the Uno’s layout: I2C is A4 (SDA) and A5 (SCL), also brought out as SDA and SCL beside AREF. The common purple BMP280 breakout has no regulator, so it runs from the Arduino Uno R4’s 3.3V pin, not 5V. Its I2C pull-ups then go to 3.3 V, which the Renesas RA4M1 (Cortex-M4) reads as high.

Pins to leave alone on the Arduino Uno R4

An Uno sketch’s source builds for the R4, but a compiled Uno program will not run on it: different chip. The R4’s pins source less current than an Uno’s, about 8 mA each, so do not drive a relay coil or a motor straight from one.

On a real bench

The Uno R4 Minima fits every Uno shield and every Uno breadboard layout, so wire the BMP280 exactly as you would on an Uno R3. It has a USB-C socket, and its VIN accepts up to 24 V where an Uno R3 stops at 12.

The code

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

BMP280 on Arduino Uno R4 I2C

#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 is the USB port; Serial1 is on pins 0 and 1, which on the R4 are free for other serial devices.

Common mistakes with the BMP280 on the Arduino Uno R4

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 R4’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 R4 Minima?

Yes. The circuit at the top of this page is an Arduino Uno R4 Minima with a BMP280, running in your browser on a simulated Renesas RA4M1 (Cortex-M4). 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 R4?

The Uno R4 keeps the Uno’s layout: I2C is A4 (SDA) and A5 (SCL), also brought out as SDA and SCL beside AREF.

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.

Start building free Open the editor