[Matplotlib-users] Live Scrolling Matplotlib graph

[Alejandro Ureta]

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(.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)















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.

}

[Benjamin Root]

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 <

Post by Alejandro Ureta
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.
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(.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)
#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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