voltmeter.py

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#!/usr/bin/env python
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# Copyright (C) 2015, Jack O'Quin
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"""
This module handles voltage messages from the Arduino Mega 2560
mounted on BWI segbots, publishing them as ROS
sensor_msgs/BatteryState messages.
"""

# enable some python3 compatibility options:
from __future__ import absolute_import, print_function, unicode_literals

import re

import rospy
from sensor_msgs.msg import BatteryState
from geometry_msgs.msg import Vector3


class VoltmeterMessages(object):
    """ ROS message translation for UTexas BWI segbot voltage obtained
    from Arduino sensor. """
    def __init__(self):
        self.parser = re.compile(
            r'V(\d+(\.\d*)?|\.\d+)')
        """ Extracts voltage reading from the Arduino serial message.
        :returns: voltage data string reported, may be empty.
        """
        self.pub = rospy.Publisher('battery0', BatteryState,
                                   queue_size=1)
        # initialize constant fields in battery message
        self.battery = BatteryState(
            current=float('nan'),
            charge=float('nan'),
            capacity=float('nan'),
            design_capacity=float('nan'),
            percentage=float('nan'),
            power_supply_status=BatteryState.POWER_SUPPLY_STATUS_DISCHARGING,
            present=1)

    def publish(self, serial_msg):
        """ Publish a ROS Range message for each reading.

        :param serial_msg: voltage message from Arduino.
        :type serial_msg: str

        TODO: publish /diagnostic message, too
        """
        # Parse serial message line into a list of voltage data strings
        # containing integers.
        readings = self.parser.match(serial_msg)
        if not readings:                # no data available?
            rospy.logwarn('Invalid voltage message: ' + serial_msg)
            return

        # Format ROS battery status message
        self.battery.header.stamp = rospy.Time.now()
        self.battery.voltage = float(readings.group(1))
        rospy.logdebug('voltage: ' + str(self.battery.voltage))
        self.pub.publish(self.battery)


voltmeter = VoltmeterMessages()   # make an VoltmeterMessages instance
handler = voltmeter.publish       # declare message handler interface
""" This interface is called once for each voltage message received. """