PogzNet Weather Station

Introduction

This is just a simple Raspberry Pi based weather station. All sensor data are gathered via C programs which is then wrapped around Python to be able to do parsing, formatting and finally submission to the reporting server.

A simple architecture for this setup would be

              +---------------+   +-----------------------+
  +-------+   |Raspberry Pi   |   |Report Server          |
  |Sensors+---> Sensor reader +---> API to accept readings|
  +-------+   | Python wrapper|   | MySQL Server          |
              +---------------+   | Graphing              |
                                  +-----------------------+

Bill of Materials

• 40$ Raspberry Pi - https://www.adafruit.com/products/3055
  • Obviously you need this. Older versions of the RPi will do as long as it can accommodate all your sensors
• 10$ MPL3115A2 I2C Barometric Pressure/Altitude/Temperature Sensor - https://www.adafruit.com/products/1893
  • Accurate enough sensor for pressure, altitude and temp
• 6$ Gravity DHT11 Temperature Humidity Sensor For Arduino https://www.dfrobot.com/product-174.html
  • The MPL3115A2 reads better temperature than this, this is mainly for humidity
• 50c Headers (for DHT11) - https://www.adafruit.com/products/3002
  • For the MLP, you could wire it directly and skip this
• 2$ Female-Male/Male-Male/Male-Female Jumpers - https://www.adafruit.com/products/1957
  • Depending on the need, but for prototyping, get this and a breadboard
• 3$ Breadboard - https://www.dfrobot.com/product-575.html
  • For prototyping purposes. Get a bigger one if you have a bunch of sensors

Collection Node Setup

The collection node will be your Raspberry Pi with the sensors hooked up. Its recommended to just remotely configure it via ssh.

You will need to enable I2C via raspi-config (I2C on Pi - https://learn.sparkfun.com/tutorials/raspberry-pi-spi-and-i2c-tutorial) to be able to read data from the I2C pins. Dont forget to install i2c tools via apt-get install i2c-tools and reboot your Pi after setting this up.

You will also need to install a neat little tool called WiringPi http://wiringpi.com/download-and-install/. This will help you debug and the modules included are sometimes used in the code we will be using.

Source Code Used for Sensors

I have sourced out a couple of source codes already written for the sensors mentioned above

• DHT11 (and 22) - http://www.uugear.com/portfolio/read-dht1122-temperature-humidity-sensor-from-raspberry-pi/
• MPL3115A2 - https://github.com/ControlEverythingCommunity/MPL3115A2

One important note to consider is that I simplified the outputs to look like this:

root@PogzPi1:/home/pi# ./mpl3115a2 
Pressure = 100.66, Altitude = 55.56, Temp = 31.00
root@PogzPi1:/home/pi# ./dht
Humidity = 42.0, Temp = 30.0

For any errors, it will output an ERROR. The logic behind this is that parsing the output via Python would be easier. All are in one line separated by a comma. Catching the error would also be easier since it generally outputs a universal ERROR if something goes wrong.

get_sensor_data.py

The get_sensor_data.py is divided into several parts and configurable options.

ENDPOINT_HOST

The ENDPOINT_HOST is the IP address or the FQDN of the server which hosts the database and the front end application. This will be where you will throw your sensor data

ENDPOINT_API_URL

The ENDPOINT_API_URL starts with a / and ends with a ?. This is attached to the ENDPOINT_HOST towards the end of the source code in order for us to be able to assemble a URL where we will do the API calls.

ENDPOINT_KEY

This is a security feature to make sure that no other device is doing an API call without proper authorization. A device_id and a key should be generated from the endpoint and is saved to the database. When an API call happens, it will cross reference the device_id along with the key before accepting the values submitted to be saved to the database.

ENDPOINT_?PARAM?

These are the ENDPOINT_ variables that is part of the assembled URL. I made it customizable so that adding new sensors would be easy. This should match the values on the endpoint side.

NOTE TO SELF: Maybe I should remove this. It would be easier to mandate a certain parameter variable on both collector and server so as to make it less confusing for the ones setting this up.

run_command(COMMAND) Function

This function runs the specific C (or other) command you have on the same directory path. Expected output would be Name = Value, Another_Name = Another_Value. Expected error string should contain ERROR. It will loop until a good value is found and will automatically remove the \n and white spaces before returning the value.

If you are adding other sensors, you are expected to follow the output format and the error format. You are also exptected to know the output and catch and assign the values accordingly.