Question

我正在尝试使用覆盆子pi3中的python从血压监测器获取数据。我用谷歌搜索并找到一些使用python获取数据的例子。

我的代码：

#!/usr/bin/python
import serial
neo = serial.Serial(
    port='/dev/ttyUSB0',
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=0
)
print("connected to: " + neo.portstr)

#neo.open()      #opens port
print "Is port open ? ",neo.isOpen()    #returns true?

#ser.write("help\n");
while True:
    dataline = neo.readline();
    if dataline:
        print(dataline), neo.close()

当我使用＆＃34; sudo python pyusb.py ＆＃34;命令，它返回以下错误：

connected to: /dev/ttyUSB0
Is port open ?  True
None
Traceback (most recent call last):
  File "pyusb.py", line 18, in <module>
    dataline = neo.readline();
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 443, in read
    if not self._isOpen: raise portNotOpenError
ValueError: Attempting to use a port that is not open

如果未注释该行＆＃34; neo.open（）＆＃34;它引发了另一个错误：

connected to: /dev/ttyUSB0
Traceback (most recent call last):
  File "pyusb.py", line 13, in <module>
    neo.open()      #opens port
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 271, in open
    raise SerialException("Port is already open.")
serial.serialutil.SerialException: Port is already open.

我看过类似的问题here。但是有一个问题是覆盖＆＃34; serial.Serial（）＆＃34;方法。我无法确切地确定上面的代码有什么问题。谁能帮助我，我在那里做错了什么？

Answer 1

如果你看一下pyserial的文档，http://pyserial.readthedocs.io/en/latest/shortintro.html#readline它说你必须在使用readline()时指定超时。这是因为readline()在每次传输结束时等待EOL字符。尝试使用以下内容将超时增加到1：

import serial
neo = serial.Serial(
    port='/dev/ttyUSB0',
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=1
)
print("connected to: " + neo.portstr)

while True:
    dataline = neo.readline();
    print dataline

python serial问题：ValueError：尝试使用未打开的端口

1 个答案: