The plot will autoscale base on the data that has been plotted to it. In
your code, you are repeatedly calling plot(), albeit with a scrolled
version of the data, but all of the previous calls to plot() are still
visible. Also, no x-coordinate information is provided to the calls to
plot(), so each new call to plot() only overlays on top of the previous
calls.
I also see that you are using the interactive mode. This isn't really
necessary. I would suggest reading through some of the animation examples
to see how to automatically update your plot:
http://matplotlib.org/examples/animation/index.html . I would particularly
point out the animate_decay example. While it isn't a scrolling example,
you can see how to update an existing plot with new data from a generator.
It would then just be a matter of updating the x-limits for each update.
I hope that helps!
Ben Root
On Wed, Jun 3, 2015 at 12:17 PM, Alejandro Ureta
alejandro.r.ur...@gmail.com wrote:
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 it scrolling. 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.
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(0,500) #Set y min and max
values
plt.title('Frequency vs Time') #Plot the title
plt.grid(True) #Turn the grid on
plt.ylabel('Frequency (pulses/sec)')#Set
ylabels
plt.plot(tempF, 'ro-', label='pulses/sec') #plot the temperature
plt.legend(loc='upper left')#plot the legend
plt2=plt.twinx()#Create a second y axis
plt.ylim(0,500) #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
pres = 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(pres)#Building our pressure
array by appending P readings
drawnow(makeFig) #Call drawnow to update our
live graph
plt.pause(.01) #Pause Briefly. Important to
keep drawnow from crashing
cnt=cnt+1
if(cnt10):#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)
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.
}
--
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