live_graph.py

#!/usr/bin/python2
import pylab as plt
import collections
import random
import time
import serial
maxsamples = 1000

Y1 = collections.deque([0] * maxsamples)
Y2 = collections.deque([0] * maxsamples)
Y3 = collections.deque([0] * maxsamples)

plt.ion()
plt.figure(figsize=(20,10))

graph1 = plt.plot(Y1)[0]
graph2 = plt.plot(Y2)[0]
graph3 = plt.plot(Y3)[0]

ser = serial.Serial('/dev/ttyUSB0', 19200, bytesize=8, parity='N', stopbits=1, timeout=None)

old = bytearray()
while True:
    try:
        new = ser.read(21)
    except serial.serialutil.SerialException:
        time.sleep(0.1)
        continue

    old += new

    if '\n' in old:
        (line, old) = old.split('\n', 1)
    else:
        continue

    print line
    parts = line.split(' ')

    if len(parts) != 4:
        continue

    try:
        y1 = float(parts[0])/10.0
        y2 = float(parts[2])/100.0
        y3 = float(parts[3])/100.0
    except ValueError:
        continue

    Y1.append(y1)
    Y1.popleft()

    Y2.append(y2)
    Y2.popleft()

    Y3.append(y3)
    Y3.popleft()

    graph1.set_ydata(Y1)
    graph2.set_ydata(Y2)
    graph3.set_ydata(Y3)

    plt.draw()
    plt.axis([0,maxsamples, 15,100])