BMP180 Barometric Pressure Sensor

The BMP180 is a high-precision barometric pressure and temperature sensor from Bosch. It communicates over I2C and can measure barometric pressure with an accuracy as low as ±0.02 hPa, making it suitable for weather stations, altimeters, and indoor navigation. It is the successor to the BMP085.

For this interfacing you need the following components:

• Arduino board (Uno, Nano, Mega, etc.)
• BMP180 pressure sensor module
• Breadboard and jumper wires
• USB cable to connect Arduino to your computer

Schematic

The BMP180 communicates over the I2C bus. Connect it to the Arduino as follows:

BMP180 Module        Arduino
------------         -------
VIN           -->    5V (or 3.3V depending on module)
GND           -->    GND
SCL           -->    A5 (Uno/Nano) or SCL (Mega/Due)
SDA           -->    A4 (Uno/Nano) or SDA (Mega/Due)

Most BMP180 modules include built-in pull-up resistors and a voltage regulator, so no external components are needed.

Pin Map

I2C pins vary by Arduino board:

• Uno / Nano / Mini: SDA → A4, SCL → A5
• Mega 2560: SDA → 20, SCL → 21
• Leonardo: SDA → 2, SCL → 3
• Due / Zero: SDA → SDA, SCL → SCL (dedicated pins)

Install necessary Library

Install the Adafruit BMP085 Library (which also supports BMP180) via the Library Manager (Tools > Manage Libraries):

1. Adafruit BMP085 Library by Adafruit
2. Adafruit Unified Sensor Library by Adafruit (required dependency)

Alternatively, using arduino-cli:

arduino-cli lib install "Adafruit BMP085 Library"
arduino-cli lib install "Adafruit Unified Sensor"

Code with complete explanation

This sketch reads temperature, pressure, and calculates altitude from the BMP180, printing the values to the Serial Monitor.

#include <Adafruit_BMP085.h>

Adafruit_BMP085 bmp;

void setup()
{
  Serial.begin(9600);
  Serial.println("BMP180 Barometric Pressure Sensor Test");

  if (!bmp.begin())
  {
    Serial.println("Could not find a valid BMP180 sensor, check wiring!");
    while (1) {}
  }
}

void loop()
{
  float temperature = bmp.readTemperature();
  float pressure    = bmp.readPressure();        // in Pascals
  float altitude    = bmp.readAltitude();         // in meters (assumes sea-level pressure of 101325 Pa)

  // Read pressure at sea-level (requires known altitude at your location)
  float sealevelPressure = bmp.readSealevelPressure(); // Pa

  // Estimate altitude using a custom sea-level pressure (e.g., from a weather report)
  float altitudeCorrected = bmp.readAltitude(sealevelPressure);

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" °C");

  Serial.print("Pressure: ");
  Serial.print(pressure / 100.0); // convert Pa to hPa (millibar)
  Serial.println(" hPa");

  Serial.print("Sea-level Pressure: ");
  Serial.print(sealevelPressure / 100.0);
  Serial.println(" hPa");

  Serial.print("Altitude (estimated): ");
  Serial.print(altitude);
  Serial.println(" m");

  Serial.print("Altitude (corrected): ");
  Serial.print(altitudeCorrected);
  Serial.println(" m");

  Serial.println();
  delay(2000);
}

Code breakdown

• #include <Adafruit_BMP085.h> — includes the library for BMP085 and BMP180 sensors.
• Adafruit_BMP085 bmp — creates a BMP085/BMP180 object.
• bmp.begin() — initializes the I2C connection and returns true if the sensor is found. The while (1) loop halts execution if the sensor is missing.
• bmp.readTemperature() — returns temperature in degrees Celsius.
• bmp.readPressure() — returns absolute pressure in Pascals (1 hPa = 100 Pa).
• bmp.readAltitude() — estimates altitude in meters assuming standard sea-level pressure (101325 Pa).
• bmp.readSealevelPressure() — calculates what the pressure would be at sea level given the current altitude measurement. This is useful for weather station use.
• bmp.readAltitude(sealevelPressure) — a more accurate altitude estimate when you provide the current sea-level pressure (e.g., from a local weather report).

Steps to perform this interfacing

1. Connect the BMP180 module to the Arduino as shown in the schematic above.
2. Install the Adafruit BMP085 Library and its dependency via the Library Manager.
3. Copy the code into the Arduino IDE.
4. Select the correct board and port (Tools > Board and Tools > Port).
5. Upload the sketch to the Arduino.
6. Open the Serial Monitor (Tools > Serial Monitor, set baud rate to 9600).
7. Observe temperature, pressure, sea-level pressure, and altitude readings every 2 seconds.

Caution

• The BMP180 is a 3.3V sensor. If using a bare chip (not a module), connect VCC to 3.3V, NOT 5V, or you will damage the sensor. Most breakout modules include a voltage regulator and can accept 5V.
• The I2C address of the BMP180 is fixed at 0x77 and cannot be changed. You cannot connect two BMP180 sensors on the same I2C bus without a multiplexer.
• Altitude readings are estimates based on pressure. They are affected by weather changes and require calibration with a known reference pressure for accuracy.
• The BMP180’s pressure range is 300–1100 hPa. It will not function correctly at very high altitudes (above about 9000 m / 30000 ft).
• Allow the sensor to stabilize for a few seconds after power-up before relying on readings.
• Avoid exposing the sensor to water or condensing humidity — the BMP180 is not waterproof and the measurement diaphragm can be damaged by liquid ingress.