Convert sample point to time values - python-2.7

Question

import sys
import serial
import numpy as np
import matplotlib.pyplot as plt
from collections import deque
port = "COM11"
baud = 9600
timeout=1
ser = serial.Serial()
ser.port = port
ser.baudrate = baud
ser.timeout = timeout
a1 = deque([0.0]*100)
#ax = plt.axes(xlim=(0, 100), ylim=(0, 1000))
line, = plt.plot(a1)
plt.ion()
plt.ylim([0,1000])
try:
ser.open()
except:
sys.stderr.write("Error opening serial port %s\n" % (ser.portstr) )
sys.exit(1)
#ser.setRtsCts(0)
while 1:
# Read from serial port, blocking
data = ser.read(1)
# If there is more than 1 byte, read the rest
n = ser.inWaiting()
data = data + ser.read(n)
#sys.stdout.write(data)
print(a1)
a1.appendleft((data))
datatoplot = a1.pop()
line.set_ydata(a1)
plt.draw()
I am getting a plot between serial port values and sample points. I want to plot serial plot values vs time. Is there a way to convert sample points to time values, something like how to we convert sample point to frequency values using freqs = scipy.fftpack.fftfreq(n, d)
Thanks

Answer 1

If you want to plot the data against time from the start of the program, then:
import time
t0 = time.time()
tlist = deque([np.nan] * 100)
while 1:
# read the serial data ...
# when you have read a sample, capture the time difference
# and put it into a queue (similarly to the data values)
deltat = time.time() - t0
dlist.appendleft((deltat))
# remember to pop the data, as well
dlist.pop()
a1.pop()
# set the x and y data
line.set_xdata(tlist)
line.set_ydata(a1)
# draw it
plt.draw()
Now you have the number of seconds from the start of the program on the X axis.
If you want to have the real time shown, then use datetime.datetime objects:
import datetime
dlist = deque([datetime.datetime.now()] * 100)
while 1:
# capture the serial data ...
dilst.appendleft((datetime.datetime.now()))
# everything else as above
This should give you a plot with real time on the X axis.

Answer 2

import sys
import serial
import numpy as np
import matplotlib.pyplot as plt
import time
from collections import deque
from scipy import arange
port = "COM13"
baud = 9600
timeout=1
ser = serial.Serial()
ser.port = port
ser.baudrate = baud
ser.timeout = timeout
t0=time.time()
tlist = deque([np.nan]*10)
a1 = deque([0.0]*10)
#ax = plt.axes(xlim=(0, 100), ylim=(0, 1000))
line, = plt.plot(a1)
plt.ion()
plt.ylim([-100,100])
plt.grid(b=True,which= 'major' , color= 'g' , linestyle= '--')
#plt.grid(b=True,which= 'minor' , color= '-m' , linestyle= '--')
try:
ser.open()
except:
sys.stderr.write("Error opening serial port %s\n" % (ser.portstr) )
sys.exit(1)
#ser.setRtsCts(0)
while 1:
# Read from serial port, blocking
data = ser.read(1)
# If there is more than 1 byte, read the rest
n = ser.inWaiting()
data = data + ser.read(n)
#sys.stdout.write(data)
#print(a1)
#data1=int(data)-128
deltat = time.time() - t0
tlist.appendleft((deltat1))
datatoplot = tlist.pop()
a1.appendleft((data))
datatoplot = a1.pop()
line.set_xdata(tlist)
line.set_ydata(a1)
plt.hold(False)
plt.draw()
This is the complete code I used, and yes I had already changed that line.pop . But as I explained earlier in the comment I am not able to get the time values in x axis