Arduino_Monitor.py

"""
Listen to serial, return most recent numeric values
Lots of help from here:
http://stackoverflow.com/questions/1093598/pyserial-how-to-read-last-line-sent-from-serial-device
"""
from threading import Thread
import time
import serial

last_received = ''


def receiving(serial_port):
    global last_received
    buffer = ''
    while True:
        buffer += serial_port.read_all()
        if '\n' in buffer:
            lines = buffer.split('\n')  # Guaranteed to have at least 2 entries
            last_received = lines[-2]
            # If the Arduino sends lots of empty lines, you'll lose the last
            # filled line, so you could make the above statement conditional
            # like so: if lines[-2]: last_received = lines[-2]
            buffer = lines[-1]


class SerialData(object):

    def __init__(self, **kwargs):
        try:
            self.serial_port = serial.Serial(**kwargs)
        except serial.serialutil.SerialException:
            # no serial connection
            self.serial_port = None
        else:
            Thread(target=receiving, args=(self.serial_port,)).start()

    def next(self):
        if self.serial_port is None:
            # return anything so we can test when Arduino isn't connected
            return 100
        # return a float value or try a few times until we get one
        for i in range(40):
            raw_line = last_received
            try:
                return float(raw_line.strip())
            except ValueError:
                print 'bogus data', raw_line
                time.sleep(.005)
        return 0.

    def __del__(self):
        if self.serial_port is not None:
            self.serial_port.close()


if __name__ == '__main__':
    s = SerialData('com4')
    for i in range(500):
        time.sleep(.015)
        print s.next()