Plots bitalino signals in realtime and saves as video

gistfile1.py

import bitalino
import numpy
import signal
import sys
import time
import threading
import datetime
from matplotlib import pyplot as plt
from matplotlib import animation
from multiprocessing import Process,Value,Queue
from Queue import Empty

addr =  '/dev/cu.bitalino-DevB'
# Channel
# 0 - EMG
# 1 - EDA
# 2 - ECG
# 3 - Acelerometer
# 4 - Lux
channel           = 2
sampling_rate     = 100
read_buffer_size  = 10
plot_size         = sampling_rate*5
video_file_name   = 'bitalino_'+str(channel)+'_'+datetime.datetime.now().strftime("%Y%m%d_%H%M%S")+'.mp4'

should_exit = Value('b',0)
q = Queue()
plot_data = [0]*plot_size
miny,maxy = 0,0
num_samples = 0


fig = plt.figure(figsize=(15, 6))
ax = fig.add_subplot(111)
line, = ax.plot(range(-plot_size,0), plot_data, 'b-')
#extra_args=['-vcodec', 'libx264']
writer = animation.writers['ffmpeg'](fps=sampling_rate/read_buffer_size )
writer.setup(fig, video_file_name, 100,)

def plot_add_samples(samples):
	global plot_data, num_samples
	plot_data = plot_data[len(samples):] + samples
	num_samples += len(samples)

def plot_set_data():
	marginy = (maxy-miny)*0.05
	if marginy > 0: ax.set_ylim([miny-marginy,maxy+marginy]) 
	line.set_xdata(range(num_samples-plot_size,num_samples))
	line.set_ydata(plot_data)
	ax.relim()
	ax.autoscale(True,'x',True)
	
def plot_init():
	global miny,maxy
	samples = q.get()
	plot_add_samples(samples)
	miny,maxy = min(samples), max(samples)
	plot_set_data()	
	return line,

def plot_update(i):
	global plot_data, miny, maxy, num_samples
	try:
		while True:
			samples = q.get_nowait()
			plot_add_samples(samples)
			miny,maxy = min(miny,min(samples)), max(maxy,max(samples))	

	except Empty:
			plot_set_data()
			writer.grab_frame()
	return line,

		
def read_data(q,should_exit):
	signal.signal(signal.SIGINT, signal.SIG_IGN)
	print "Started acquisition process"
	device = bitalino.BITalino()
	print device.find(True)
	device.open(addr, sampling_rate) 
	device.start([channel]) 
	print "Bitalino started"

	while should_exit.value == 0:
		try:    
			data_acquired = device.read(read_buffer_size)
			samples = data_acquired[5,:].tolist()
			q.put(samples)

		except Exception, e:
			print "Acquisiton: ", e
	device.stop() 
	device.close()
	print "Finished acquisition process"

p = Process(target=read_data,args=(q,should_exit))	
p.start()

def exit():
	print "Exiting"
	should_exit.value = 1
	p.join()

def signal_handler(signal, frame):
	exit()

signal.signal(signal.SIGINT, signal_handler)

anim = animation.FuncAnimation(fig, plot_update, init_func=plot_init, interval=100,  blit=False)
plt.show()
writer.finish()
exit()