This tutorial was one of the winners of INTERNET of THINGS 2016 Contest. Thanks a lot! In this project, we will program a RPi and an Arduino, to work together to capture data from sensors, sending them to the Web.
The functions will be split be split between the two devices:
- Capture Temperature and Humidity data via an digital sensor (DHT-11)
- Capture light information (simulating a simple ADC)
- Communicate with Web, sending all captured data
- Capture analog data with accuracy
The video bellow, shows data being captured by RPi and sent to ThingSpeak.com website:
This project was part of my tutorial: Mobile Station prototype for Environmental Data Capture ("a Mars Rover emulator") that will be expand here for better understanding. The "Mars Rover" project was also featured on MagPi magazine.
For this project, we will need:
- Rapsberry Pi2
- WiFi dongle
- DHT-11 Temperature and Humidity Sensor
- Arduino Nano
- LDR (Light Depend Resistor)
First, get the Library from Github:
git clone https://github.com/adafruit/Adafruit_Python_DHT.gi...
Installing the Library:
sudo apt-get update sudo apt-get install build-essential python-dev python-opensslcd /Home/Pi/Adafruit_Python_DHT sudo python setup.py install
Test the sensor running the file AdafruitDHT.py at monitor. Enter as parameters: 11 (Sensor DHT11) and 4 (GPIO where the sensor is connected):
sudo python /Home/Pi/Adafruit_Python_DHT/examples/AdafruitDHT.py 11 4
- The result should be the temperature and humidity read by the sensor.
For the basic settings of the DH-11 sensor with the RPi, and sending data to internet, a great help was get from this tutorial:
From what was learned, the important is
- Setting a Channel at ThingSpeak.com:
- Run the Python Code bellow for tests
The general idea for this step of the project was learned from:
A LDR and a Capacitor was connected to GPIO24. If there is light, the GPIO24 will return HIGH and w/o light “LOW”.
The Python Code used in this test:
The next step was to get "light intensity data". To add the LDR to RPi the best is to convert the analog signal from the sensor to a digital value using an external ADC (Analog to Digital Converter). The RPi does not have an internal ADC as the Arduino. If you do not have an ADC, a good approximation is to use a capacitor charging/discharging technic. The "Raspberry Pi Cookbook" gives the solution (note that Instead the Potentiometer, a LDR could be used):
import RPi.GPIO as GPIO import time GPIO.setmode(GPIO.BCM) a_pin = 25 b_pin = 23 def discharge(): GPIO.setup(a_pin, GPIO.IN) GPIO.setup(b_pin, GPIO.OUT) GPIO.output(b_pin, False) time.sleep(0.005) def charge_time(): GPIO.setup(b_pin, GPIO.IN) GPIO.setup(a_pin, GPIO.OUT) count = 0 GPIO.output(a_pin, True) while not GPIO.input(b_pin): count = count + 1 return count def analog_read(): discharge() return charge_time() while True: print(analog_read()) time.sleep(1)
The best is to use the Arduino to capture this kind of info and send it to RPi. The result will be more accurate.
The previous Python Code was updated, including the new sensors:
A simple solution to send alarms, is t send a Tweet directly from the website. In this case the ”React” feature of ThingSpeak.com can be used. Please see the details how to define an React in the video at introduction of this tutorial.
The Arduino used was the NANO that is so powerful as the UNO but on a "small form factor".
For tests purposes, A potentiometer was connected to Arduino analog port A0 and the value transmitted via Serial to the RPi. In the test, RPi will be reading a Keyboard (connect to it or thru VNC) and depending on the command, the Arduino LED will be toggle "ON/OFF". Below the Arduino and Python code used on the tests:
Once the Arduino is connected with RPi, additional data captured by Arduino can also be sent to the Web, together with other data captured by the DH11 and LDR.
The Python code used to send data to the Website was changed to also included the data captured by Arduino (potentiometer value).
As always, I hope this project can help others to find their way in the exciting world of electronics and IoT!
The updated code for this project can be found at GITHUB: https://github.com/Mjrovai/MJRoBot-IoT-RPi-Arduino
For more projects, please visit my blog: MJRoBot.org
Saludos from the south of the world!