[Matplotlib-users] Problems with Real Time Plotting

[Alejandro U. <ale...@gm...>]

Hi, I am trying to get a live scrolling graph built from data send by two
arduino sensors. Although live data is being shown in the graph  I am not
able to get  the x axis scrolling. Actually, after reaching the point
established  by the counter (in this case cnt>10), the plotting stops. The
arduino and Python codes I am working with are included below. I would very
much appreciate if you can help me getting the scrolling graph working.

ARDUINO CODE

#include "Wire.h"    // imports the wire library for talking over I2C
#include "Adafruit_BMP085.h"  // import the Pressure Sensor Library
Adafruit_BMP085 mySensor;  // create sensor object called mySensor

float tempC;  // Variable for holding temp in C
float tempF;  // Variable for holding temp in F
float pressure; //Variable for holding pressure reading

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

void loop() {
tempC = mySensor.readTemperature(); //  Be sure to declare your variables
tempF = tempC*1.8 + 32.; // Convert degrees C to F
pressure=mySensor.readPressure(); //Read Pressure


Serial.print(tempF);
Serial.print(" , ");
Serial.println(pressure);
delay(250); //Pause between readings.
}




​PYTHON CODE
​import serial # import Serial Library
import numpy  # Import numpy
import matplotlib.pyplot as plt #import matplotlib library
from drawnow import *

tempF= []
pressure=[]
arduinoData = serial.Serial('com6', 115200) #Creating our serial object
named arduinoData
plt.ion() #Tell matplotlib you want interactive mode to plot live data
cnt=0

def makeFig(): #Create a function that makes our desired plot
    plt.ylim(0,90)                                 #Set y min and max values
    plt.title('My Live Streaming Sensor Data')      #Plot the title
    plt.grid(True)                                  #Turn the grid on
    plt.ylabel('Temp F')                            #Set ylabels
    plt.plot(tempF, 'ro-', label='Degrees F')       #plot the temperature
    plt.legend(loc='upper left')                    #plot the legend
    plt2=plt.twinx()                                #Create a second y axis
    plt.ylim(0,90)                           #Set limits of second y axis-
adjust to readings you are getting
    plt2.plot(pressure, 'b^-', label='Pressure (Pa)') #plot pressure data
    plt2.set_ylabel('Pressrue (Pa)')                    #label second y axis
    plt2.ticklabel_format(useOffset=False)           #Force matplotlib to
NOT autoscale y axis
    plt2.legend(loc='upper right')                  #plot the legend


while True: # While loop that loops forever
    while (arduinoData.inWaiting()==0): #Wait here until there is data
        pass #do nothing
    arduinoString = arduinoData.readline() #read the line of text from the
serial port
    dataArray = arduinoString.split(',')   #Split it into an array called
dataArray
    temp = float( dataArray[0])            #Convert first element to
floating number and put in temp
    P =    float( dataArray[1])            #Convert second element to
floating number and put in P
    tempF.append(temp)                     #Build our tempF array by
appending temp readings
    pressure.append(P)                     #Building our pressure array by
appending P readings
    drawnow(makeFig)                       #Call drawnow to update our live
graph
    plt.pause(.000001)                     #Pause Briefly. Important to
keep drawnow from crashing
    cnt=cnt+1
    if(cnt>10):                            #If you have 50 or more points,
delete the first one from the array
        tempF.pop(0)                       #This allows us to just see the
last 50 data points
        pressure.pop(0)