Plot DHT11 Data Using Raspberry Pi and Arduino UNO

This instructable explains how I plot temperature sensor DHT11 data using Arduino Uno and Raspberry Pi. In this temperature sensor is connected with Arduino Uno and Arduino Uno is connected serially with Raspberry Pi. At Raspberry Pi Side, matplotlib,numpy and drawnow libraries are used to plot graphs.

Step 1: Things Needed for the Project

1. Raspberry Pi

2. Arduino Uno

3. DHT11 Temperature Sensor

4. Jumper Wires

5. Breadboard

Step 2: Download and Install Arduino IDE in Raspberry Pi

Note :- You can use Arduino IDE of windows,Linux or Mac to upload sketch in Arduino UNO.

First step is to install Arduino IDE for that open browser in Raspberry Pi and open the link given below

Arduino Previous IDE

Then download the Linux ARM version and extract it using command

tar  -xf file name

After extracting you will see a new directory. Here I am using arduino-1.8.2 IDE. Then go to directory by using command.

cd arduino-1.8.1

To run Arduino IDE, use this command in arduino-1.8.2 directory

./arduino

How to use libraries

To install any libraries in Arduino , simply download the library and paste in arduino 1.8.2 ==> libraries folder .

NOTE:- Make sure there is no ( - ) in library folder for ex (DHT-sensor). If there is any (-),rename it .

we will use two libraries in this instructable, DHT_Sensor and Adafruit_Sensor

Step 3: Code for Arduino

Now, lets get python and Arduino talking together. Firstly we need a simple program to get the Arduino sending data over the serial port. The following program is a simple program that will have the Arduino count and send the data to the serial port.

Arduino Code

#include "DHT.h"
 float tempC;  // Variable or holding temp in C float tempF;  // Variable for holding temp in F float humidity; //Variable for holding pressure reading

#define DHTPIN 7 // what digital pin we're connected to

#define DHTTYPE DHT11 // DHT 11

//#define DHTTYPE DHT22 // DHT 22 (AM2302), AM2321

//#define DHTTYPE DHT21 // DHT 21 (AM2301)

// Initialize DHT sensor.

DHT dht(DHTPIN, DHTTYPE);  

void setup(){
Serial.begin(115200); //turn on serial monitor 

dht.begin();   //initialize dht }

void loop() {
tempC = dht.readTemperature(); //  Be sure to declare your variables

humidity = dht.readHumidity(); // Read Humidity

Serial.print(tempC);

Serial.print(" , ");

Serial.print(humidity);

Serial.print("\n"); // for new line
delay(2000); //Pause between readings. }

Once sketch is compiled , select board and port and upload it.

Step 4: Setup Raspberry Pi

Once code is uploaded, Install some libraries so that we can plot graph of data which is coming serially from Arduino Uno.

1. PySerial is a library which provides support for serial connections over a variety of different devices. To install it use command.

Sudo apt-get install python-serial

2. Numpy is a package that defines a multi-dimensional array object and associated fast math functions that operate on it. It also provides simple routines for linear algebra and FFT (Fast Fourier Transform) and sophisticated random-number generation. You can install it in many ways either use apt package or pip. Here I am installing using pip for that first we have to install pip

sudo apt-get install python-pip python-dev build-essential

sudo pip install numpy

or if you wanna use apt package

sudo apt install python-numpy

3. Matplotlib is a 2D plotting library which provides an object-oriented API for embedding plots into applications using general-purpose GUI toolkits like Tkinter, wxPython, Qt, or GTK+. To install it use command

sudo pip install matplotlib

or

sudo apt install python-matplotlib

4. Drawnow is generally used to see the results after each iteration as we use "imshow" in MATLAB. To install it use command

sudo pip install drawnow

Step 5: Python Scipt

Next step is to write a python script for that you can use any editor to write it.

1. Plot data in one graph

import serial                      # import Serial Library

import numpy                    # Import numpy

import matplotlib.pyplot as plt                 #import matplotlib library

 from drawnow import *

tempC = []     #Empty array<br>humidity = []

arduino = serial.Serial("/dev/ttyACM0", 115200)

plt.ion()                   # interactive mode to plot live data<br>count = 0

def makeFig():              #Create a function that makes our desired plot
   plt.ylim(20,30)                              #Set y min and max values     

plt.title('Real Time DHT11 Data')      #Plot the title

plt.grid(True)                                  #Turn the grid on

plt.ylabel('Temp C')                            #Set ylabel

plt.plot(tempC,'b^-', label='Degree C')       #plot the temperature

plt.legend(loc='upper right')                    #plot the legend

plt2=plt.twinx()                                #Create a second y axis

plt.ylim(50,70)                           #Set limits of second y axis

plt2.plot(humidity, 'g*-', label='Humidity') #plot pressure data

plt2.set_ylabel('Humidity')                    #label second y axis

plt2.ticklabel_format(useOffset=False)           

plt2.legend(loc='upper left')

while True: # While loop that loops forever
    while (arduino.inWaiting()==0): #Wait here until there is data         

               pass #do nothing  

     arduinoString = arduino.readline()

     dataArray = arduinoString.split(',')   #Split it into an array

     temp = float( dataArray[0])

     hum = float( dataArray[1])

     tempC.append(temp)

     humidity.append(hum)

     drawnow(makeFig)

     plt.pause(.000001)

     count=count+1<br>     
     if(count>20):    #only take last 20 data if data is more it will pop first    

          tempC.pop(0)         

          humidity.pop(0)

2. To plot humidity and temperature separately

import serial # import Serial Library
import numpy  # Import numpy 

import matplotlib.pyplot as plt #import matplotlib library 

from drawnow import *

tempC = []     #Empty array 

humidity = []

arduino = serial.Serial("/dev/ttyACM0", 115200)   #Serial port to which arduino is connected and Baudrate

plt.ion() #Tell matplotlib you want interactive mode to plot live data

def CreatePlot(): #Create a function that makes our desired plot
    plt.subplot(2,1,1)  #Height,Width,First plot

    plt.ylim(22,34)                                 #Set y min and max values
    plt.title('Real Time DHT11 Data')      #Plot the title
    

    plt.grid(True)                                  #Turn the grid on
    

    plt.ylabel('Temp C')                            #Set ylabels
    

    plt.plot(tempC,'b^-', label='Degree C')       #plot the temperature
  

    plt.legend(loc='upper center')                    #plot the legend

    plt.subplot(2,1,2)  # Height,Width,Second plot

    plt.grid(True)

    plt.ylim(45,70)             #Set limits of second y axis
    plt.plot(humidity, 'g*-', label='Humidity (g/m^3)') #plot humidity data
    

    plt.ylabel('Humidity (g/m^3)')    #label second y axis
  

    plt.ticklabel_format(useOffset=False)           #to stop autoscale y axis
   

    plt.legend(loc='upper center')

while True: # While loop that loops forever
    while (arduino.inWaiting()==0): #Wait here until there is data
        pass #do nothing
  

  arduinoString = arduino.readline() #read the data from serial port

   dataArray = arduinoString.split(',')   #Split it into an array

    temp = float( dataArray[0])            #Convert first element to floating number and put in temp

    hum = float( dataArray[1])            #Convert second element to floating number and put in hum
  

    tempC.append(temp)                     #Build our tempC array by appending temp reading
    

    humidity.append(hum)                     #Building our humidity array by appending hum reading
    

   drawnow(CreatePlot)
    

   plt.pause(.000001)
    

   count=count+1

   if(count>20):    #only take last 20 data if data is more it will pop first
        tempC.pop(0) # pop out first element
        

        humidity.pop(0)

Step 6: Circuit Diagram

Arduino ==> DHT11

3.3V ==> VCC

GND ==> GND

D7 ==> OUT

Step 7: Result