arduino.py

import serial

MESSAGE_THROTTLE = 1
MESSAGE_DIRECT = 2
MESSAGE_CALIBRATE = 3


class Arduino():
    def __init__(self):
        self.ser = serial.Serial(
            "/dev/ttyUSB0",
            baudrate=9600,
            parity=serial.PARITY_NONE,
            stopbits=serial.STOPBITS_ONE,
            bytesize=serial.EIGHTBITS,
            writeTimeout=0,
            timeout=10,
            rtscts=False,
            dsrdtr=False,
            xonxoff=False)

        # Motors disabled by default. Its a safety thing.
        self.motors_enabled = False

        while (self.ser.readline() == ""):
            print("Waiting for serial")
        print ("Got serial input, now we can continue")
        self.ser.write("Hello")

    def enable_motors(self, enable):
        """ Called when we want to enable/disable the motors.
            When disabled, will ignore any new motor commands. """
        self.motors_enabled = enable

    def throttle(self, left_micros, right_micros):
        """ Send motors command to change speed in servo
            microseconds using ramps. """
        command = "[%d, %d, %d]\n" % \
            (MESSAGE_THROTTLE, left_micros, right_micros)
        self.ser.write(command)
        print("Writing %s" % command)

    def direct_micros(self, left_micros, right_micros):
        """ Send motors speed in servo microseconds.
            WARNING: this method tells the motors
            to change speed IMEDIATELY without ramping. """
        command = "[%d, %d, %d]\n" % \
            (MESSAGE_DIRECT, left_micros, right_micros)
        print("Writing %s" % command)
        self.ser.write(command)

    def calibrate_motors(self, left_mid, right_mid):
        """ Not sure yet, I believe this method will
            send appropriate calibration speeds to ESC's
            so that they are properly calibrated. """
        command = "[%d, %d, %d]\n" % (MESSAGE_CALIBRATE, left_mid, right_mid)
        self.ser.write(command)
        print("Writing %s" % command)

    def read_sensor(self):
        """ Read a sensor value and return it. """
        command = "[4]"
        self.ser.write(command)
        print("Writing %s" % command)
        s = self.ser.readline()  # Of the format "(A,xxx)\n"
        s_value = s
        print("Read sensor %s" % s_value)
        try:
            i_value = int(s_value)
            return i_value
        except:
            print("Cannot parse message {} as number, returning 0"
                  ).format(s_value)
            return 0