Windows 上的 Python 串行：读取串行信息时 USB 监视器循环不起作用

Question

我有一个网站和一个 USB rfid 阅读器。 python 脚本监视与 rfid 阅读器的 USB 连接。如果在脚本开头没有连接阅读器，则网站内容向右滑动并显示连接 rfid 阅读器的 USB 电缆的说明。如果然后连接，它会向左滑动并显示用户使用 rfid 卡来识别自己。阅读器只有在视口中有特定内容时才开始阅读 rfid 数据。但是我没有进入这一步，因为串行通信似乎被阻止了。

import serial 
import mysql.connector
import time
import datetime
from serial.tools import list_ports
from selenium import webdriver
from selenium.webdriver.firefox.firefox_binary import FirefoxBinary
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.common.keys import Keys
capabilities = webdriver.DesiredCapabilities().FIREFOX
capabilities["marionette"] = True
binary = FirefoxBinary('C:/Program Files/Mozilla Firefox/firefox.exe')
driver = webdriver.Firefox(firefox_binary=binary, capabilities=capabilities, executable_path="C:/Python37x64/geckodriver.exe")

# ------------------ USB monitorloop -------------------------------------

stop = 0
swipe = 0
driver.get('https://website.php')
while True:
    try:
        myports = [tuple(p) for p in list(serial.tools.list_ports.comports())]
        arduino_port = [port for port in myports if 'COM3' in port ][0]
        def check_presence(correct_port, interval=0.1):
        global swipe
        global stop
            while True:
                myports = [tuple(p) for p in list(serial.tools.list_ports.comports())]
                if arduino_port not in myports:
                    stop = 1
                    swipe = swipe + 1
                    if swipe == 1:
                        print ("Arduino has been disconnected!")
                        driver.execute_script("$('.in_viewport,#usb_connect, #header_usb_connect').animate({ left: '+='+'100vw'});");
                        time.sleep(1.0)
                    else:
                        continue
                else:
                    if swipe >= 1 and stop == 1:
                        swipe = 0
                        print ("Arduino connected!")
                        driver.execute_script("$('.in_viewport,#usb_connect, #header_usb_connect').animate({ left: '-='+'100vw'});");
                        time.sleep(1.0)
                    else:
                        continue
        import threading
        port_controller = threading.Thread(target=check_presence, args=(arduino_port, 0.5,))
        port_controller.setDaemon(True)
        port_controller.start()
        break
    except:
        stop = 1
        if swipe == 0:
            print("Connect USB cable")
            driver.execute_script("$('.in_viewport,#usb_connect, #header_usb_connect').animate({ left: '+='+'100vw'});");
            time.sleep(1.0)
            swipe = 1
            continue
        else:
            time.sleep(1.0)


# --------- connecting to COM 3 and database -----------------------
device_port = 'COM3'
baud = 9600
while True:
    try:
        print ("Trying...",device_port)
        connect_arduino = serial.Serial(device_port, baud)
        print ("Successfully connected to",device_port)
        print ("Try to connect to database")
        db = mysql.connector.connect(host="",port="",user="",passwd="",db="") 
        print ("Successfully connected to database")
        break
    except mysql.connector.Error as err:
        print("Something went wrong: {}".format(err))
        print ("failed to connect to database")
        time.sleep(1)
        continue
# ------- reading the card identification number and current time -------------        
while True:
    try:
        print ("Reading USB device")
        rfid_data = connect_arduino.readline()
        now = datetime.datetime.now()
        print (rfid_data.decode('utf-8'),"read on", now.strftime("%d-%m-%Y"), "at", now.strftime("%H:%M:%S"))
        time.sleep(2)
        break
    except:
        time.sleep(2)
        continue

我希望能够serial.readline()rfid_data，但我认为监视器环路阻塞了串行端口以及与端口的通信。

Answer 1

很抱歉在这里介绍基础知识，但是您是否检查过您可以使用其他东西（例如终端仿真器）读取串行端口？

我在串口方面遇到了无穷无尽的问题，尤其是 USB 版本。当我不想要它时，要么是其他东西抓住了端口，要么是在将 USB 映射到 COM 号时出现了问题。有时您需要其他东西来仔细检查它们。

Answer 2

我认为您最大的问题是阅读循环中的break 语句。它按预期工作并打破了循环的正常流程，因此您只需调用一次串口读取函数。

改善循环的一种方法是检查 RX 缓冲区是否为空：

while True:
    if connect_arduino.inWaiting() != 0:
        print ("Reading USB device")
        rfid_data = connect_arduino.readline()
        now = datetime.datetime.now()
        print (rfid_data.decode('utf-8'),"read on", now.strftime("%d-%m-%Y"), "at", now.strftime("%H:%M:%S"))

如果您仅在确定缓冲区中有数据并且知道 RFID 阅读器发送 \r\n 作为终止字符时才调用 readline()，则您确定您将始终读取标签。

编辑：看来你想要的是嗅探端口。您不能直接从两个不同的应用程序保持相同的端口打开。如果你在 Windows 上，你可以试试this solution。