Question

我是python的初学者，我正在尝试从usb集线器连接到我的计算机的几个传感器（湿度，温度，压力传感器......）中读取数据。我的主要目标是每隔五分钟记录这些传感器的不同值，然后将其存储以进行分析。

我已经获得了所有data sheets and manuals我的传感器（来自Hygrosens Instruments），我知道它们是如何工作的以及它们发送的数据类型。但我不知道如何阅读它们。以下是我尝试使用pyserial。

import serial #import the serial library
from time import sleep #import the sleep command from the time library
import binascii

output_file = open('hygro.txt', 'w') #create a file and allow you to write in it only. The name of this file is hygro.txt

ser = serial.Serial("/dev/tty.usbserial-A400DUTI", 9600) #load into a variable 'ser' the information about the usb you are listening. /dev/tty.usbserial.... is the port after plugging in the hygrometer, 9600 is for bauds, it can be diminished
count = 0
while 1:
    read_byte = ser.read(size=1)

所以现在我想找到数据行的结尾，因为我需要的测量信息是以＆＃39; V＆＃39;开头的行，如果是传感器的数据表，那么说一行结束，所以我想一次读一个字节然后查找＆＃39;＆＃39;然后＆＃39; c＆＃39;然后＆＃39; r＆＃39; ，然后＆＃39;＆gt;＆＃39;。所以我想这样做：

while 1:
    read_byte = ser.read(size=8) #read a byte
    read_byte_hexa =binascii.hexlify(read_byte) #convert the byte into hexadecimal

    trad_hexa = int(read_byte_hexa , 16) #convert the hexadecimal into an int in purpose to compare it with another int
    trad_firstcrchar = int('3c' , 16) #convert the hexadecimal of the '<' into a int to compare it with the first byte    
    if (trad_hexa == trad_firstcrchar ): #compare the first byte with the '<'    
        read_byte = ser.read(size=1) #read the next byte (I am not sure if that really works)
        read_byte_hexa =binascii.hexlify(read_byte)# from now I am doing the same thing as before
        trad_hexa = int(read_byte_hexa , 16)
        trad_scdcrchar = int('63' , 16)
        print(trad_hexa, end='/')# this just show me if it gets in the condition
        print(trad_scdcrchar)    
        if (trad_hexa == trad_scdcrchar ):    
            read_byte = ser.read(size=1) #read the next byte 
            read_byte_hexa =binascii.hexlify(read_byte)
            trad_hexa = int(read_byte_hexa , 16)
            trad_thirdcrchar = int('72' , 16)
            print(trad_hexa, end='///')
            print(trad_thirdcrchar)    
            if (trad_hexa == trad_thirdcrchar ):    
                read_byte = ser.read(size=1) #read the next byte 
                read_byte_hexa =binascii.hexlify(read_byte)
                trad_hexa = int(read_byte_hexa , 16)
                trad_fourthcrchar = int('3e' , 16)
                print(trad_hexa, end='////')
                print(trad_fourthcrchar)    
                if (trad_hexa == trad_fourthcrchar ):    
                    print ('end of the line')

但我不确定它是否有效，我的意思是我认为它没有时间阅读第二个字节，我正在阅读的第二个字节，它不完全是第二个字节。这就是为什么我想使用缓冲区，但我真的不知道如何做到这一点。我会去寻找它，但如果有人知道一种更简单的方法来做我想做的事情，我准备尝试了！谢谢

Answer 1

您似乎认为该传感器的通信协议的行尾字符是4个不同的字符：<，c，r和>。但是，所提到的是carriage return，通常由<cr>表示，在许多编程语言中仅由\r表示（即使它看起来像2个字符，它代表只是一个字符。）

通过逐行读取传感器中的数据，您可以大大简化代码，因为协议是结构化的。以下是帮助您入门的内容：

import time

def parse_info_line(line):
    # implement to your own liking
    logical_channel, physical_probe, hardware_id, crc = [line[index:index+2] for index in (1, 3, 5, 19)]
    serialno = line[7:19]
    return physical_probe

def parse_value_line(line):
    channel, crc = [line[ind:ind+2] for ind in (1,7)]
    encoded_temp = line[3:7]
    return twos_comp(int(encoded_temp, 16), 16)/100.

def twos_comp(val, bits):
    """compute the 2's compliment of int value `val`"""
    if (val & (1 << (bits - 1))) != 0: # if sign bit is set e.g., 8bit: 128-255
        val = val - (1 << bits)        # compute negative value
    return val                         # return positive value as is

def listen_on_serial(ser):
    ser.readline() # do nothing with the first line: you have no idea when you start listening to the data broadcast from the sensor
    while True:
        line = ser.readline()
        try:
            first_char = line[0]
        except IndexError:  # got no data from sensor
            break
        else:
            if first_char == '@':  # begins a new sensor record
                in_record = True
            elif first_char == '$':
                in_record = False
            elif first_char == 'I':
                parse_info_line(line)
            elif first_char == 'V':
                print(parse_value_line(line))
            else:
                print("Unexpected character at the start of the line:\n{}".format(line))
            time.sleep(2)

twos_comp函数是written by travc，当你有足够的声誉并打算使用他的代码时，我们鼓励你提出他的答案（即使你赢了，它也是＆＃ 39; s仍然是一个很好的答案，我刚刚赞成它。 listen_on_serial也可以得到改进（许多Python程序员会识别交换结构并用字典而不是if... elif... elif...来实现它），但这只是为了让你入门。

作为测试，以下代码提取模拟传感器发送一些数据（使用回车符作为行尾标记的行分隔），我从您链接到的pdf复制（ FAQ_terminalfenster_E.pdf ）。

>>> import serial
>>> import io
>>> 
>>> ser = serial.serial_for_url('loop://', timeout=1)
>>> serio = io.TextIOWrapper(io.BufferedRWPair(ser, ser), newline='\r', line_buffering=True)
>>> serio.write(u'A1A0\r'  # simulation of starting to listen halfway between 2 records
...     '$\r'              # marks the end of the previous record
...     '@\r'              # marks the start of a new sensor record
...     'I0101010000000000001B\r'  # info about a sensor's probe
...     'V0109470D\r'              # data matching that probe
...     'I0202010000000000002B\r'  # other probe, same sensor
...     'V021BB55C\r')             # data corresponding with 2nd probe
73L
>>> 
>>> listen_on_serial(serio)
23.75
70.93
>>>

请注意，当行尾字符不是TextIOWrapper（换行字符）时，使用\n是recommended by the pyserial docs，因为还answered here。

从python中的各种usb设备读取和存储各种数据

1 个答案: