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.
- Connect Vin (red wire on STEMMA version) to the power supply, 3-5V is fine. Use the same voltage that the microcontroller logic is based off of. For most Arduinos, that is 5V
- Connect GND (black wire on STEMMA version) to common power/data ground
- Connect the SCK (yellow wire on STEMMA version) pin to the I2C clock SCL pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A5, on a Mega it is also known as digital 21 and on a Leonardo/Micro, digital 3
- Connect the SDI (blue wire on STEMMA version) pin to the I2C data SDA pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A4, on a Mega it is also known as digital 20 and on a Leonardo/Micro, digital 2
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:
- Connect Vin to the power supply, 3V or 5V is fine. Use the same voltage that the microcontroller logic is based off of. For most Arduinos, that is 5V
- Connect GND to common power/data ground
- Connect the SCK pin to Digital #13 but any pin can be used later
- Connect the SDO pin to Digital #12 but any pin can be used later
- Connect the SDI pin to Digital #11 but any pin can be used later
- Connect the CS pin Digital #10 but any pin can be used later
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 install the Adafruit_BMP280 library (code on our github repository). It is available from the Arduino library manager so we recommend using that.
From the IDE open up the library manager...
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:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use
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
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! Check the SPI reference to see what pins to use.
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
Text editor powered by tinymce.
