This is a Python 3 package that enables Raspberry Pi to read various sensors.

Supported devices include:

• DS18B20 temperature sensor
• BMP180 pressure and temperature sensor
• HTU21D humidity and temperature sensor
• SHT20 humidity and temperature sensor
• MCP3004 A/D Converter (MCP3008 also compatible)

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 dist-upgrade

Install this package:

sudo pip3 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 Raspberry Pi to do so.

sudo raspi-config, enter Interfacing Options, enable the protocols you need.

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/
• For I2C sensors, use i2cdetect -y 1
• For SPI sensors, you should know which CS pin you use

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.

• 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('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(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(msl=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(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

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

from sensor import SHT20
# I2C bus=1, Address=0x40
sht = SHT20(1, 0x40)
h = sht.humidity() # read humidity
print(h) # namedtuple
print(h.RH) # relative humidity
t = sht.temperature() # read temperature
print(t) # namedtuple
print(t.C) # Celsius
h, t = sht.all() # read both at once

• Analog sensors (e.g. photoresistor) cannot interface with Raspberry Pi directly. They have to go through an A/D converter.

from sensor import MCP3004
# SPI bus=0, CS=0, V_ref=3.3V
mcp = MCP3004(bus=0, addr=0, vref=3.3)
mcp.voltage(0) # read voltage on channel 0