This is a Python package that enables Raspberry Pi to read various sensors (and interact with some non-sensors). It has been tested on Python 2.7 running on Raspbian on Raspberry Pi 2 Model B.

Supported devices include:

• DS18B20 temperature sensor
• BMP180 pressure and temperature sensor
• HTU21D humidity and temperature sensor
• ML8511 UV sensor
• MCP3004 A/D Converter (MCP3008 also compatible)
• LCD1602 and LCD2004 display

The chief motivation for this package is educational. I am teaching a Raspberry Pi course, and find it very troublesome for students having to download a separate library every time they use another sensor. With this package, download once and they are set (for my course, anyway). I hope you find it useful, too.

It is best to update Linux first.

sudo apt-get update
sudo apt-get upgrade

For Raspbian Jessie, you may have to do the following to fix pip (because of its using an older version of requests):

sudo apt-get remove python-pip
sudo easy_install -U pip

Install this package:

sudo pip install sensor

But the sensor package would not work by itself. Communicating with sensors often requires some sort of serial protocol, such as 1-wire, I2C, or SPI. You have to know which sensor speaks which, and set up Linux and Python accordingly.

sudo nano /boot/config.txt, add this line:

dtoverlay=w1-gpio

Reboot.

sudo apt-get install i2c-tools python-smbus

sudo nano /etc/modules, add this line:

i2c-dev

sudo nano /boot/config.txt, add this line:

dtparam=i2c1=on

Reboot.

sudo apt-get install python-dev
sudo pip install spidev

sudo nano /boot/config.txt, add this line:

dtparam=spi=on

Reboot.

Unlike many libraries out there, this library knows no default bus number and no default device address. I want learners to be explicitly aware of those numbers, even if they are fixed.

For example:

• I2C bus is numbered 1
• SPI bus is numbered 0

To find out individual sensor's address:

• For 1-wire sensors, go to /sys/bus/w1/devices/, and look for a long sequence of numbers
• For I2C sensors, use i2cdetect -y 1
• For SPI sensors, you should know which CS pin you used

Unlike many libraries out there, this library does not return a simple Celcius degree when reading temperatures, does not return a simple hPa value when reading pressure, does not return a simple RH% when reading humidity, etc. Instead, I return a namedtuple representing the quantity, which offers two benefits:

• No more conversion needed. Suppose you get a Temperature called t, you may access the Celcius degree by t.C as easily as you do Fahrenheit by t.F.
• Namedtuples may have methods. For example, a Pressure has a method called altitude(), which tells you how high you are above mean sea level. It is convenient and intuitive.

Keep reading to see how it really works ...

• Temperature, 1-wire

• To find out the sensor's address:

  $ cd /sys/bus/w1/devices/
  $ ls
  28-XXXXXXXXXXXX  w1_bus_master1
  

Read the sensor as follows:

from sensor import DS18B20

ds = DS18B20.DS18B20('28-XXXXXXXXXXXX')
t = ds.temperature()  # read temperature

print t    # this is a namedtuple
print t.C  # Celcius
print t.F  # Fahrenheit
print t.K  # Kelvin

• Pressure + Temperature, I2C
• Use i2cdetect -y 1 to check address. It is probably 0x77.

from sensor import BMP180

# I2C bus=1, Address=0x77
bmp = BMP180.BMP180(1, 0x77)

p = bmp.pressure()  # read pressure
print p             # namedtuple
print p.hPa         # hPa value

t = bmp.temperature()  # read temperature
print t                # namedtuple
print t.C              # Celcius degree

p, t = bmp.all()  # read both at once
print p           # Pressure namedtuple
print t           # Temperature namedtuple

# Look up mean sea level pressure from local observatory.
# 1009.1 hPa is only for example.
a = p.altitude(1009.1)

print a     # Altitude ...
print a.m   # in metre
print a.ft  # in feet

• Humidity + Temperature, I2C
• Use i2cdetect -y 1 to check address. It is probably 0x40.

from sensor import HTU21D

# I2C bus=1, Address=0x40
htu = HTU21D.HTU21D(1, 0x40)

h = htu.humidity()  # read humidity
print h             # namedtuple
print h.RH          # relative humidity

t = htu.temperature()  # read temperature
print t                # namedtuple
print t.F              # Fahrenheit

h, t = htu.all()  # read both at once

• UV intensity, Analog output
• Cannot interface with Pi directly. Must do so via an A/D converter, e.g. MCP3004.
• Output is expressed in mW/cm² (milli-Watt per cm²), and cannot be translated into a UV index simply.

# another style of import
from sensor.ML8511 import ML8511
from sensor.MCP3004 import MCP3004

# A/D converter
# SPI bus=0, CS=0, V_ref=3.3V
mcp = MCP3004(0, 0, 3.3)

# analog output -> channel 0 on MCP3004
ml = ML8511(mcp, 0)

uv = ml.uv()  # read UV intensity

print uv         # namedtuple
print uv.mW_cm2  # mW/cm2

• Not a sensor, obviously. Useful for displaying sensor data.
• Use i2cdetect -y 1 to check address. It is probably 0x27.
• Both are used the same way. Just supply the correct class name, as below.

from sensor.LCD1602 import LCD1602

# I2C bus=1, Address=0x27
lcd = LCD1602(1, 0x27)

lcd.display('Nick Lee', 1)   # show my name on line 1
lcd.display('Hong Kong', 2)  # show my city on line 2

lcd.clear()