# Determining the Pressure and Altitude Using GY-68 BMP180 and Arduino

## Overview

In many projects such as flying robots, weather stations, improving routing performance, sports and etc. measuring pressure and altitude is very important. In this tutorial, you’ll learn how to use the BMP180 sensor, which is one of the most commonly used sensors for measuring the pressure.

## What Is the Barometric Pressure?

Barometric pressure or atmospheric pressure results from the weight of the air on the earth. This pressure is about 1 kg per square centimeter at the sea level.

There are several units to express the atmospheric pressure, that can easily be converted to each other. The SI unit for measuring the pressure is Pascal (Pa).

Unit 1hPa equivalent
Pascal(Pa) 100
Atmosphere(atm) 0.000986923
Milibar(MBR) 1
Millimeters Mercury(mmHg) 0.750063755
Inch of Mercury(inHg) 0.02953
Torr(torr) 0.750061683
Pounds per square inch(psi) 0.014503774
Newtons per square meter(N/m^2) 100
The barometric pressure has an approximately linear inverse ratio with the altitude from the sea level so if we measure the barometric pressure of a place, we can calculate the altitude from the sea level using a simple mathematical operation.

## GY-68 BOSCH BMP180 Pressure Sensor Features

One of the most common sensors for measuring the pressure and altitude is BOSCH BMP180. The most important features of this module are as follow:

• Pressure measurement range of 300 to 1100hPa
• -0.1hPa measuring accuracy for absolute pressure
• 12hPa measuring accuracy for relative pressure
• Low power consumption (5μA in standard mode and one sample per second)
• Internal temperature sensor with a precision of 0.5 °C
• Supporting I2C protocol for communication
• Fully calibrated

## Required Materials

### Hardware Components

 Arduino UNO R3 × 1 BOSH BMP180 × 1 Jumper Wire × 1

### Software Apps

 Arduino IDE

## How to Use GY-68 BMP180 Pressure Sensor with Arduino?

This sensor is available as a module for easy use. The main parts of the BMP180 sensor module are:
• BMP180 sensor
• A 3.3-volt regulator. This regulator lets you connect the module to 5V.
• Required pull up resistors to communicate I2C properly

### Circuit

BMP180_Breakout_Arduino_Library

## Calculation of Absolute Pressure with Different Units and Altitude from the Sea Level

``````*/

BMP180

modified on 23 Apr 2019
by Saeed Hosseini @ Electropeak
Home

*/

#include <SFE_BMP180.h>
#include <Wire.h?

SFE_BMP180 pressure;

#define ALTITUDE 943.7 // Altitude of Electropeak Co. in meters

void setup() {
Serial.begin(9600);
if (pressure.begin())
Serial.println("BMP180 init success");
else
{

Serial.println("BMP180 init fail\n\n");
Serial.println("Check connection");
while (1);
}

}

void loop() {

char status;
double T, P, p0, a;

status = pressure.startTemperature();
if (status != 0)
{
delay(status);
status = pressure.getTemperature(T);
if (status != 0)
{

Serial.print("temperature: ");
Serial.print(T, 2);
Serial.println(" deg C ");

status = pressure.startPressure(3);
if (status != 0)
{

delay(status);
status = pressure.getPressure(P, T);
if (status != 0)
{

Serial.print("absolute pressure: ");
Serial.print(P, 2);
Serial.print(" hpa = ");
Serial.print(P * 100, 2);
Serial.print(" pa = ");
Serial.print(P * 0.000986923, 2);
Serial.print(" atm = ");
Serial.print(P * 0.750063755, 2);
Serial.print(" mmHg = ");
Serial.print(P * 0.750061683, 2);
Serial.print(" torr = ");
Serial.print(P * 0.014503774, 2);
Serial.println(" psi");

p0 = pressure.sealevel(P, ALTITUDE); // we're at 943.7 meters
Serial.print("relative (sea-level) pressure: ");
Serial.print(p0, 2);
Serial.println(" hpa ");;

a = pressure.altitude(P, p0);
Serial.print(a, 0);
Serial.println(" meters ");
}
else Serial.println("error retrieving pressure measurement\n");
}
else Serial.println("error starting pressure measurement\n");
}
else Serial.println("error retrieving temperature measurement\n");
}
else Serial.println("error starting temperature measurement\n");
Serial.println("==========================================================================");
delay(5000);
}``````

Let’s check the process of pressure and altitude calculation more accurately:

According to the above algorithm, first we start to calculate the temperature using `startTemperature()`, then we store the temperature in variable T using `getTemperature(T)`. After that, we calculate the pressure with `startPressure(3)`. The number 3 is the maximum resolution that can be changed between 0 and 3. using `getPressure(P)` we store the absolute pressure in variable P. The amount of this pressure is in hPa, which can be converted to different units according to the previous table. The absolute pressure changes with altitude. To remove the effect of the altitude on the calculated pressure, we should use the `sealevel(P,ALTITUDE)` function according to the altitude stored in the ALTITUDE variable, and store the measured value in an arbitrary variable, such as p0. Use `altitude(P,p0)` to calculate your altitude. This function calculates the altitude in the meter.
##### Note
that you can insert your altitude from the sea level for the ALTITUDE variable defined at the beginning of the code.

## Make an Altimeter!

The BMP180 pressure sensor, like many other pressure sensors, measures the absolute pressure, and the absolute pressure changes with the change of the altitude. So you can calculate the relative altitude by measuring the pressure.

``````/*

BMP180 - altimeter

modified on 23 Apr 2019
by Saeed Hosseini @ Electropeak
Home

*/

#include <SFE_BMP180.h>
#include <Wire.h>

SFE_BMP180 pressure;

double baseline;

void setup()
{
Serial.begin(9600);
Serial.println("REBOOT");

if (pressure.begin())
Serial.println("BMP180 init success");
else
{

Serial.println("BMP180 init fail (disconnected?)\n\n");
while (1);
}

Serial.print("baseline pressure: ");
Serial.print(baseline);
Serial.println(" hpa");
}

void loop()
{
double a, P;

a = pressure.altitude(P, baseline);

Serial.print("relative altitude: ");
if (a >= 0.0) Serial.print(" ");
Serial.print(a, 1);
Serial.println(" meters, ");
delay(500);
}

{
char status;
double T, P, p0, a;
status = pressure.startTemperature();
if (status != 0)
{
delay(status);
status = pressure.getTemperature(T);
if (status != 0)
{
status = pressure.startPressure(3);
if (status != 0)
{
delay(status);
status = pressure.getPressure(P, T);
if (status != 0)
{
return (P);
}
else Serial.println("error retrieving pressure measurement\n");
}
else Serial.println("error starting pressure measurement\n");
}
else Serial.println("error retrieving temperature measurement\n");
}
else Serial.println("error starting temperature measurement\n");
}``````
The `startPressure(3)` function calculates the absolute pressure value. Since the pressure changes with the change of the temperature and humidity, we store the initial pressure in baseline variable. According to this value and instantaneous pressure, the `altitude(P,baseline)` function calculates the relative altitude in meter.

## What’s Next?

• Try to calculate the pressure in case of unstable temperatures.

### More To Explore

• James Francis

Your code works amazing, but i am using this in a rocket. I am very very new to coding. I plan to ignite an engine at a certain altitude. I was wondering if you could help do this, all i need is for the code, at a certain altitude, to turn on one of the pins. I am thinking this is simple, but I have no idea how to do it. Thanks!

July 1, 2020 at 9:22 pm
• Cristofer Fuentes

#define IGNITE_ALTITUDE 300 // the altitude to give power to the ignite system
#define PIN_INGNITE 4 // the ignite system is connected to this pin

That is very easy
pinMode( PIN_INGNITE , OUTPUT); // set the pin as output for give energy to the ignite system in the setup()

if (A > IGNITE_ALTITUDE) // check the altitude in the loop()
digitalWrite(PIN_INGNITE, HIGH); // give energy to the pin for start the ignite system

July 22, 2020 at 6:32 am