The most popular electronic sensors use I2C to communicate. This is a 'shared bus' 2 wire protocol, you can have multiple sensors connected to the two SDA and SCL pins as long as they have unique addresses (check this guide for a list of many popular devices and their addresses)
Lets show how to wire up a popular BME280. This sensor provides temperature, barometric pressure and humidity data over I2C
We're going to do this in a lot more depth than our guide pages for each sensor, but the overall technique is basically identical for any and all I2C sensors.
Honestly, the hardest part of using I2C devices is figuring out the I2C address and which pin is SDA and which pin is SCL!
Because the DragonBoard 410c uses 1.8V logic levels, you will need a logic level converter to interface with most peripherals.
We recommend using a breadboard and some male-male wires.
Wiring
- Connect the DragonBoard Ground pin to the ground on the Logic Level Converter
- Connect the DragonBoard +5V pin to the red 5V rail on the breadboard.
- Connect the DragonBoard +1.8V pin to the LV pin on the Logic Level Converter
- Connect the HV pin on the Logic Level Converter to the 5V rail
- Connect the Vin pin on the BME280 to the red 5V rail on the breadboard
- Connect the Ground pin on the BME280 to the ground on the Logic Level Converter
- Connect the B1 pin on the Logic Level Converter to the BME280 SCK
- Connect the B2 pin on the Logic Level Converter to the BME280 SDI
- Connect the DragonBoard I2C0 SCL to the A1 pin on the Logic Level Converter
- Connect the DragonBoard I2C0 SDA to the A2 pin on the Logic Level Converter
Double-check you have the right wires connected to the right location, it can be tough to keep track of header pins as there are forty of them!
After wiring, we recommend running I2C detection with sudo i2cdetect -r -y 0 to verify that you see the device, in this case its address 77
Install the CircuitPython BME280 Library
OK onto the good stuff, you can now install the Adafruit BME280 CircuitPython library.
As of this writing, not all libraries are up on PyPI so you may want to search before trying to install. Look for circuitpython and then the driver you want.
(If you don't see it you can open up a github issue on circuitpython to remind us!)
Once you know the name, install it with
sudo pip3 install adafruit-circuitpython-bme280
You'll notice we also installed a dependancy called adafruit-circuitpython-busdevice. This is a great thing about pip, if you have other required libraries they'll get installed too!
We also recommend an adafruit-blinka update in case we've fixed bugs:
sudo pip3 install --upgrade adafruit_blinka
Run that code!
The finish line is right up ahead. You can now run one of the (many in some cases) example scripts we've written for you.
Check out the examples for your library by visiting the repository for the library and looking in the example folder. In this case, it would be https://github.com/adafruit/Adafruit_CircuitPython_BME280/tree/master/examples
As of this writing there's only two examples. Here's the first one:
import time
import board
import busio
import adafruit_bme280
# Create library object using our Bus I2C port
i2c = busio.I2C(board.SCLK, board.SDA)
bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)
# OR create library object using our Bus SPI port
#spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
#bme_cs = digitalio.DigitalInOut(board.D10)
#bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
# change this to match the location's pressure (hPa) at sea level
bme280.sea_level_pressure = 1013.25
while True:
print("\nTemperature: %0.1f C" % bme280.temperature)
print("Humidity: %0.1f %%" % bme280.humidity)
print("Pressure: %0.1f hPa" % bme280.pressure)
print("Altitude = %0.2f meters" % bme280.altitude)
time.sleep(2)
Save this code to your DragonBoard by copying and pasting it into a text file, downloading it directly from the DragonBoard, etc.
Then in your command line run
sudo python3 bme280_simpletest.py
The code will loop with the sensor data until you quit with a Control-C
Here's the second example:
"""
Example showing how the BME280 library can be used to set the various
parameters supported by the sensor.
Refer to the BME280 datasheet to understand what these parameters do
"""
import time
import board
import busio
import adafruit_bme280
# Create library object using our Bus I2C port
i2c = busio.I2C(board.SCLK, board.SDA)
bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)
# OR create library object using our Bus SPI port
#spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
#bme_cs = digitalio.DigitalInOut(board.D10)
#bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
# change this to match the location's pressure (hPa) at sea level
bme280.sea_level_pressure = 1013.25
bme280.mode = adafruit_bme280.MODE_NORMAL
bme280.standby_period = adafruit_bme280.STANDBY_TC_500
bme280.iir_filter = adafruit_bme280.IIR_FILTER_X16
bme280.overscan_pressure = adafruit_bme280.OVERSCAN_X16
bme280.overscan_humidity = adafruit_bme280.OVERSCAN_X1
bme280.overscan_temperature = adafruit_bme280.OVERSCAN_X2
#The sensor will need a moment to gather inital readings
time.sleep(1)
while True:
print("\nTemperature: %0.1f C" % bme280.temperature)
print("Humidity: %0.1f %%" % bme280.humidity)
print("Pressure: %0.1f hPa" % bme280.pressure)
print("Altitude = %0.2f meters" % bme280.altitude)
time.sleep(2)
Save this code to your DragonBoard by copying and pasting it into a text file, downloading it directly from the DragonBoard, etc.
Then in your command line run
sudo python3 bme280_normal_mode.py
The code will loop with the sensor data until you quit with a Control-C
That's it! Now if you want to read the documentation on the library, what each function does in depth, visit our readthedocs documentation at
https://circuitpython.readthedocs.io/projects/bme280/en/latest/
