Live Scrolling Matplotlib graph

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.

}

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.ureta@…1972…> 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(.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.

}



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