Re: [Matplotlib-users] Live Scrolling Matplotlib graph

[Benjamin R. <ben...@ou...>]

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 <
ale...@gm...> 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)
>
>
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>
>  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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