import comedi

dev = comedi.comedi_open('/dev/comedi0')

aref = comedi.AREF_GROUND
range = 0 
chan = 4 #channel number
subdev = 0 #analog in

maxdata = comedi.comedi_get_maxdata(dev, subdev, chan)
cdi_range = comedi.comedi_get_range(dev, subdev, chan, range)

f = file('datalog.dat','ab')
while 1:
	data = comedi.comedi_data_read(dev, subdev, chan, range, aref)
	val = comedi.comedi_to_phys(data[1], cdi_range, maxdata)
	mytime = time.time()
	f.write(str(val)+'\t'+str(mytime)+'\n')
	f.flush()
	time.sleep(30)
	print val, mytime