Until this point, we've only looked at relatively simple program examples, without any real scope to them. Let's take some time to build a more complete program that actually accomplishes a practical task, a weather station.

Let's start with the hardware. We'll use a HTU21D I2C relative humidity sensor (for example, https://www.sparkfun.com/products/12064), as well as a BMP183 SPI pressure sensor (for example, https://www.adafruit.com/product/1900). Both include internal temperature sensors from which we can retrieve data, so we won't need an additional temperature sensor.

For this circuit, you will need:

Wire up the breakout boards as shown:

PyBBIO includes libraries for both sensors, so we'll use it for this program. For starters, let's look at getting the data from the sensors:

from bbio import *
from bbio.libraries.BMP183 import BMP183
from bbio.libraries.HTU21D import HTU21D

bmp = BMP183(SPI0)
htu = HTU21D(I2C2)

def setup():
  pass

def loop():
  pressure = bmp.getPressure() # in Pascals
  rh = htu.getHumidity() # in %RH
  temp = htu.getTemp() # in Celsius
  dew_point = htu.calculateDewPoint(rh, temp) # in Celsius
  pressure /= 1000.0 # convert Pa to kPa

  print "temperature : {:0.2f} C".format(temp)
  print "humidity    : {:0.2f} %RH".format(rh)
  print "pressure    : {:0.2f} kPa".format(pressure)
  print "dew point   : {:0.2f} C
".format(dew_point)
  delay(3000)
   
run(setup, loop)