Building a simple weather station with Raspberry Pi and Python

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The setup

• A headless Raspberry Pi 2 connected to the wifi network
• An AM2303 temperature and humidity sensor
• A 16x2 LCD display with LCM1602 I2C converter
• Jumper cables

Installing software

I have OSMC installed on my memory card, so first I needed to install some software:

    sudo apt-get update
    sudo apt-get install -y gcc make build-essentials python3 screen

Next, I installed raspi-config as defined here.

Following that, I needed to install pigpio:

    wget abyz.co.uk/rpi/pigpio/pigpio.zip
    unzip pigpio.zip
    make
    sudo make install

To work properly, the pigpio daemon needs to be running to transfer data. Running pigpio (in a new screen window):

    sudo pigpiod

To use the LCD display, I needed also to install smbus:

sudo -i
apt-get install python3-dev
apt-get install libi2c-dev
cd /tmp
wget http://ftp.de.debian.org/debian/pool/main/i/i2c-tools/i2c-tools_3.1.0.orig.tar.bz2 # download Python 2 source
tar xavf i2c-tools_3.1.0.orig.tar.bz2
cd i2c-tools-3.1.0/py-smbus
mv smbusmodule.c smbusmodule.c.orig # backup
wget https://gist.githubusercontent.com/sebastianludwig/c648a9e06c0dc2264fbd/raw/2b74f9e72bbdffe298ce02214be8ea1c20aa290f/smbusmodule.c # download patched (Python 3) source
python3 setup.py build
python3 setup.py install
exit

The next step was to enable i2c via raspi-config:

sudo raspi-config

Then:

• select advance menu
• select i2c
• enable it.

Use:

sudo i2cdetect -y 1

to check if the i2c device is found. If not, follow the advice here.

Wiring

The weather and humidity sensor AM2302 (DHT22) has 3 pins:

• VCC (+) - input (3V to 5.5V)
• GND (-) - ground
• OUT - data output

DTH22 pin	RPI pin
VCC	1
GND	6
OUT	7

The LCD display has 4 pins:

• VCC - input (5V)
• SDA - I2C data
• SCL - I2C clock
• GND - ground

LCM1602 pin	RPI pin
VCC	2
SDA	3
SCL	5
GND	25

Testing the configuration

To perform a simple test if everything works as expected, let's open up python3 console and run:

    import pigpio
    import DHT22
    pi = pigpio.pi()
    probe = DHT22.sensor(pi, 4)
    probe.trigger()
    temp = probe.temperature()
    humid = probe.humidity
    print("Current temperature is {}C, while current humidity is
    {}%".format(temp, humid))

Gathering data

New data from the sensor can be obtained every 2 seconds. It is streamed to my sparkfun API account.

Visualizing data

The data is visualized using the D3 library. The results can be viewed here: https://4gn3s.github.io/weatherStation/ There are separate graphs for temperature and humidity.

Ideas for the future

More sensors to measure:

• wind & speed direction
• light cycles
• air quality
• barometric pressure
• rain

Data gathering ideas

• How does the temperature in my room vary between day and night, weekdays and weekend?
• In which months there is the most rain? Which are the driest?
• How does air quality change depending on the season? Is it the worst in the winter?

Full webapp

• view radar images from the internet (served as gifs)
• show alerts (from wunderground)
• show weather forecast (from openweathermap)