經過幾天的摸索終於實現了：
在ros系統下，訂閱Twist/cmd_vel 訊息，經過USB轉串列埠通訊，實現了通過燈帶實時反映小車（差速）執行狀態的功能。
通訊部分主要依賴pyserial模組的功能實現。

#!/usr/bin/env python
#coding=utf-8
import rospy
import serial
from geometry_msgs.msg import Twist
import roslib;roslib.load_manifest('ros_bringup')
import time

ser = serial.Serial(port='/dev/tty*', baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=2,rtscts=True,dsrdtr=True)
ser.isOpen()   
res=ser.readall() 

def cmdcallback(msg):
    #rospy.Publisher('/cmd_vel',Twist)
    rospy.loginfo("Received a /cmd_vel message!")
    rospy.loginfo("Linear Components: [%f, %f, %f]"%(msg.linear.x, msg.linear.y, msg.linear.z))
    rospy.loginfo("Angular Components: [%f, %f, %f]"%(msg.angular.x, msg.angular.y, msg.angular.z))
    #####
    資料處理過程省略
    #####
    ser.write(data)
    
    s = ser.read(1)
    print(s)

def LED():
    rospy.init_node('cmd_vel_listener')
    rospy.Subscriber("/cmd_vel",Twist,cmdcallback)
    rospy.spin()
if __name__=="__main__":
    LED()