树莓Pi与SHT20传感器的最小RTU连接问题(XY MD02)

Question

我一直在尝试用Minimalmodbus建立一个简单的测温系统。各组成部分如下；

1. RPi(Raspberry pi 0)与python。3.7.3
2. USB到RS-485适配器
3. 温湿度传感器: XY-MD02(SHT20)

RPi上很好地安装了Modbus库(Minimalmodbus)，它可以成功地与Arduino Uno和Arduino Modbus库(smarmengol)通信。当与PC(windows10)连接时，还可以使用modbus主仿真软件"Modbus Poll“验证传感器的工作能力。但是当这个传感器通过USB连接到RPi到RS-485适配器时，我无法获得任何数据。我看不出它的电路有什么问题。当我在调试模式下运行它来读取寄存器时，它显示读取查询按其手册所示正确释放。错误信息只是说“没有响应错误”。即使是任何评论都将是非常感谢的。请参阅python代码和调试和错误消息如下；

#!/usr/bin/env python3
import minimalmodbus
import serial
import time

instr = minimalmodbus.Instrument('/dev/ttyUSB0',1, debug=True)
instr.serial.baudrate = 9600
instr.serial.timeout = 2

while True :
        result = instr.read_register(registeraddress=1,functioncode=4)
        print (result)
        time.sleep(3)

< Debuggin & Error Message>

MinimalModbus debug mode. Create serial port /dev/ttyUSB0
MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back) : 01 04 00 01 00 01 60 0A (8 bytes)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyUSB0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 3916373.5ms, minimum silent period: 4.01ms
MinimalModbus debug mode. Response from instrument: (0 bytes), roundtrip time: 1.0 ms. Timeout for reading : 0.0 ms.

Traceback (most recent call last) :
   File "minModTest.py", line 15, in <module>
     result = instr.read_register(registeraddress=1,functioncode=4)
   File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 486, in read_register
     payloadformat=_Payloadformat.REGISTER,
   File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1245, in _generic_command
     payload_from_slave = self._perform_command(functioncode, payload_to_slave)
   File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1322, in _perform_command
     response_bytes = self._communicate(request_bytes, number_of_bytes_to_read)
   File "/usr/local/lib/python3.7/dist-packages/minimalmodbus.py", line 1490, in _communicate
     raise NoResponseError("No communicate with the instrument (no answer)")
minimalmodbus.NoResponseError: No communication with the instrument (no answer)

*** Manual ***
<Query>
Slave Add.  Function Code   Starting Add H  Starting Add L  Q’ty H  Q’ty L  CRC H   CRC L
0x01        0x04            0x00            0x01            0x00    0x01    0x60    0x0a

<Response>
Slave Add.  FunctionCode    BytesNumber  TemperatureH   TemperatureL    CRC H   CRC L
0x01        0x04            0x02         0x01           0x31            0x79    0x74
Temperature value=0x131, converted to a decimal 305, the actual temperature value = 305 / 10 = 30.5°
Note: the temperature is signed hexadecimal number, temperature value = 0xFF33, converted to a decimal - 205, the actual temperature = -20.5 °

Answer 1

感谢您的评论。实际上，USBtoRs485_adapter( RPi )和传感器之间有4条线连接；+5V、GND、A和B。正如我所写的，这些适配器和传感器在PC(windows)上工作良好，但与RPi不兼容。配线不会是一个问题，因为同样的布线是与PC一起工作的。我需要用RPi做点什么吗？

Answer 2

你找到问题的原因了吗？下面是在我的RPi上测试的代码。它起作用了。

pi@raspberrypi:~/pythonDev/modbus $ python3 modbus01.py

MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back): '\x01\x04\x00\x01\x00\x01`\n' (01 04 00 01 00 01 60 0A)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyUSB0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 1862540.46 ms, minimum silent period: 4.01 ms.
MinimalModbus debug mode. Response from instrument: '\x01\x04\x02\x00Æ9b' (01 04 02 00 C6 39 62) (7 bytes), roundtrip time: 22.1 ms. Timeout for reading: 2000.0 ms.

198
MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back): '\x01\x04\x00\x01\x00\x01`\n' (01 04 00 01 00 01 60 0A)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyUSB0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 3023.28 ms, minimum silent period: 4.01 ms.
MinimalModbus debug mode. Response from instrument: '\x01\x04\x02\x00Æ9b' (01 04 02 00 C6 39 62) (7 bytes), roundtrip time: 22.5 ms. Timeout for reading: 2000.0 ms.

198
MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back): '\x01\x04\x00\x01\x00\x01`\n' (01 04 00 01 00 01 60 0A)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyUSB0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 3026.49 ms, minimum silent period: 4.01 ms.
MinimalModbus debug mode. Response from instrument: '\x01\x04\x02\x00Æ9b' (01 04 02 00 C6 39 62) (7 bytes), roundtrip time: 22.6 ms. Timeout for reading: 2000.0 ms.

198
MinimalModbus debug mode. Will write to instrument (expecting 7 bytes back): '\x01\x04\x00\x01\x00\x01`\n' (01 04 00 01 00 01 60 0A)
MinimalModbus debug mode. Clearing serial buffers for port /dev/ttyUSB0
MinimalModbus debug mode. No sleep required before write. Time since previous read: 3027.09 ms, minimum silent period: 4.01 ms.
MinimalModbus debug mode. Response from instrument: '\x01\x04\x02\x00Æ9b' (01 04 02 00 C6 39 62) (7 bytes), roundtrip time: 22.7 ms. Timeout for reading: 2000.0 ms.

逻辑分析仪上的modbus RS485

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Answer 3

下面是用于我的项目的适配器。祝你好运:) usb到rs485适配器

下面是用于我的项目的适配器。祝你好运:)