Reading data from Voltcraft VC506 multimeter for long-term measurements

multimeter.py

#!/usr/bin/python
'''
    Read data from Voltcraft VC506
    and write to file or console
    
    see:
    https://pythonhosted.org/pyserial/
'''
import serial
import time
import sys, argparse


def readlineCR(port):
    rv = ''
    while True:
        ch = port.read()
        rv += ch
        if ch=='\r' or ch=='':
            return rv


# check for command line arguments
#parser = argparse.ArgumentParser(description='Voltcraft VC506 log', formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser = argparse.ArgumentParser(description='Voltcraft VC506 log')
parser.add_argument('-p',nargs='?', default='/dev/ttyUSB0', help='set serial Port (default: %(default)s)')
parser.add_argument('-f',nargs='?', default='', help='file name for logfile, no logfile if empty')
parser.add_argument('-c',type=int,default=-1,help='number of measurements, stop with ctrl+c (default: inf)')
parser.add_argument('-d',type=float,default=1,help='delay between masurements in seconds (default: %(default)d)')
parser.add_argument('-ts',action='store_true',help='add time stamp to measurement')
parser.add_argument('-nh',action='store_true',help='do not print header text')
parser.add_argument('-cs',action='store_true',help='use comma seperator')
args = parser.parse_args()

# setting the parameter
PORT = args.p
NUM_MEAS = args.c
NO_HEADER = args.nh
USE_SEP = args.cs
USE_TS = args.ts
OUTFILE = args.f.strip()
if args.d < 0.25:
    TIME_STEP = 0.25
else:
    TIME_STEP = args.d

ser = serial.Serial(PORT, baudrate=1200, bytesize=7, parity='N', stopbits=1, timeout=2.0)
ser.flushInput()
ser.flushOutput()

if ser.isOpen():
    if not NO_HEADER:
        print 'Reading from port '+PORT+' \n'
else:
    print '!error, port not opened'
    sys.exit(3)

# building the header
if NO_HEADER:
    meas = []
else:
    if USE_TS:
        meas = ['Time Range Value Unit']
    else:
        meas = ['Range Value Unit']
    if USE_SEP:
        meas[0].replace(' ',',')
    print meas[0]
# running the measurement
st = time.time()
try:
    while(NUM_MEAS):
        if (NUM_MEAS > 0):
            NUM_MEAS -= 1
        et = time.time()
        ser.write('\r')
        val=readlineCR(ser)
        if val=='':
            sys.exit(2)
        if USE_TS:
            meas.append('%0.2f ' %(et-st)+val.strip())
        else:
            meas.append(val.strip())
        if USE_SEP:
            meas[-1].replace(' ',',')
        print meas[-1] 
        time.sleep(TIME_STEP)
except (KeyboardInterrupt):
    if not NO_HEADER:
        print '\nstopping..'
except (SystemExit):
    print '\n! no data, connection lost?\nstopping..'
except Exception, e:
    print '! some error'

ser.close()

if not ser.isOpen():
    if not NO_HEADER:
        print 'Port '+PORT+' closed.'
else:
      print '! closing error'

if OUTFILE != '':
    with open(OUTFILE, 'w') as myof:
        for e in meas:
            myof.write(e+'\n')