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)
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