How to take the derivative of a Signal in Python?

Question

I am new at Python language and coding.

I am trying to acquire and differentiate a live signal from a Arduino UNO Board using the USB Serial. So far, I am acquiring the data with no problems, but I cant get information about how to differentiate it.

Would you guys help me on that or point me out where I can get some information on this stuff.

I would really appreciate your help.

Here is my code

Obs.: I am begginer :D

# -*- coding: utf-8 -*-

from collections import deque
import serial
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui
import numpy as np
arduinoData = serial.Serial('COM4', 4800)

win = pg.GraphicsWindow()
win.setWindowTitle('pyqtgraph example: Scrolling Plots')

#    In these examples, the array size is fixed.
p1 = win.addPlot()
p2 = win.addPlot()

data1= [0,0]
vector=deque()

for i in range(300):

    string = arduinoData.readline()
    stringx = string.split(',')

    time=float(stringx[0])
    distance=float(stringx[1])
    vector=(time, distance) 
    vectorx = np.array(vector)
    data1=np.vstack((data1,vectorx))   

curve1 = p1.plot(data1)
curve2 = p2.plot(data1)
ptr1 = 0



def update1():
    global data1, curve1, ptr1

    data1[:-1] = data1[1:]  

    string = arduinoData.readline()

    stringx = string.split(',')
    time=float(stringx[0])
    distance=float(stringx[1])
    vector=(time, distance)
    vectorx=np.array(vector)
    data1[-1]=vectorx
    #print(data1)

    curve1.setData(data1)

    ptr1 += 1
    curve2.setData(data1)
    curve2.setPos(ptr1, 0)

# update all plots
def update():
    update1()

timer = pg.QtCore.QTimer()
timer.timeout.connect(update)
timer.start(50)



## Start Qt event loop unless running in interactive mode or using pyside.
if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()

Answer 1

"To differentiate a signal" is an expression that is seldom used in English (although it seems to be correct according to Google). That's why you and @zvone had a misunderstanding. It's probably better to say that you want to "take the derivative" of the signal.

Anyway, the numpy.gradient function can do this.