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Oasis-Knowledge
BMP-280: Atmospheric Pressure
BMP-280 Setup Guide
Here’s a setup guide for connecting the BMP-280 to an Arduino.
Pinouts
Power Pins:
SPI Logic pins:
All pins going into the breakout have level shifting circuitry to make them 3-5V logic level safe. Use whatever logic level is on Vin!
If you want to connect multiple BMP280's to one microcontroller, have them share the SDI, SDO and SCK pins. Then assign each one a unique CS pin.
I2C Logic pins:
Leave the other pins disconnected
Assembly
The assembly pix use the BME280 but it is identically shaped/sized as the BMP280
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Prepare the header strip:
Cut the strip to length if necessary. It will be easier to solder if you insert it into a breadboard - long pins down
Add the breakout board:
Place the breakout board over the pins so that the short pins poke through the breakout pads
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Solder
Be sure to solder all pins for reliable electrical contact.
(For tips on soldering, be sure to check out our ).
You're done! Check your solder joints visually and continue onto the next steps
Arduino Test
You can easily wire this breakout to any microcontroller, we'll be using an Arduino. For another kind of microcontroller, as long as you have 4 available pins it is possible to 'bit-bang SPI' or you can use two I2C pins, but usually those pins are fixed in hardware. Just check out the library, then port the code.
I2C Wiring
Use this wiring if you want to connect via I2C interface
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SPI Wiring
Since this is a SPI-capable sensor, we can use hardware or 'software' SPI. To make wiring identical on all Arduinos, we'll begin with 'software' SPI. The following pins should be used:
Later on, once we get it working, we can adjust the library to use hardware SPI if you desire, or change the pins to other
Download Adafruit_BMP280 library
To begin reading sensor data, you will need to . It is available from the Arduino library manager so we recommend using that.
From the IDE open up the library manager...
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And type in adafruit bmp280 to locate the library. Click Install
You'll also need to install the Adafruit Unified Sensor library
We also have a great tutorial on Arduino library installation at:
Load Demo
Open up File->Examples->Adafruit_BMP280->bmp280test and upload to your Arduino wired up to the sensor
Depending on whether you are using I2C or SPI, change the pin names and comment or uncomment the following lines.
#define BMP_SCK 13
#define BMP_MISO 12
#define BMP_MOSI 11
#define BMP_CS 10
Adafruit_BMP280 bmp; // I2C
//Adafruit_BMP280 bmp(BMP_CS); // hardware SPI
//Adafruit_BMP280 bmp(BMP_CS, BMP_MOSI, BMP_MISO, BMP_SCK);
Once uploaded to your Arduino, open up the serial console at 9600 baud speed to see data being printed out
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Temperature is calculated in degrees C, you can convert this to F by using the classic F = C * 9/5 + 32 equation.
Pressure is returned in the SI units of Pascals. 100 Pascals = 1 hPa = 1 millibar. Often times barometric pressure is reported in millibar or inches-mercury. For future reference 1 pascal =0.000295333727 inches of mercury, or 1 inch Hg = 3386.39 Pascal. So if you take the pascal value of say 100734 and divide by 3389.39 you'll get 29.72 inches-Hg.
You can also calculate Altitude. However, you can only really do a good accurate job of calculating altitude if you know the hPa pressure at sea level for your location and day! The sensor is quite precise but if you do not have the data updated for the current day then it can be difficult to get more accurate than 10 meters.
Library Reference
You can start out by creating a BMP280 object with either software SPI (where all four pins can be any I/O) using
Adafruit_BMP280 bmp(BMP_CS, BMP_MOSI, BMP_MISO, BMP_SCK);
Or you can use hardware SPI. With hardware SPI you must use the hardware SPI pins for your Arduino - and each arduino type has different pins!
In this case, you can use any CS pin, but the other three pins are fixed
Adafruit_BMP280 bmp(BMP_CS); // hardware SPI
or I2C using the default I2C bus, no pins are assigned
Adafruit_BMP280 bmp; // I2C
Once started, you can initialize the sensor with
if (!bmp.begin()) {
Serial.println("Could not find a valid BMP280 sensor, check wiring!");
while (1);
}
begin() will return True if the sensor was found, and False if not. If you get a False value back, check your wiring!
Reading temperature and pressure is easy, just call:
bmp.readTemperature()
bmp.readPressure()
Temperature is always a floating point, in Centigrade. Pressure is a 32 bit integer with the pressure in Pascals. You may need to convert to a different value to match it with your weather report.
It's also possible to turn the BMP280 into an altimeter. If you know the pressure at sea level, the library can calculate the current barometric pressure into altitude
Sources
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