Use of struct.unpack python

[vbrozik (Václav Brožík)]

Yesterday you opened one topic about your serial communication. I offered you a solution for the NUL character which seemed to be unwanted:

Serial read with python

I think it is practically impossible that wrong parameter settings of the serial port would cause it to read extra NUL characters (b'\x00', also called null character) and otherwise read correct data. It looks like your device sends null-terminated records. PuTTY and other terminals do not show NUL characters. The following code should resolve the problem. Just add the serial port parameters (baudrate etc.) as needed, adjust the timeout and you will probably want to collect the received values …

I think the solution should work but we have no response from you and you left us speculating a) Why is the NUL there? b) Do you have correct parameters for the serial communication? c) Do not you need flow control? etc.

Please first test if my code resolves the problem, confirm what is the source of the NUL characters and let us know about the results and possible problems with the code I offered. After that let’s continue here.

---

Something for the preparation here:

@juniorprogrammer

I’m sending an array what looks like this in python:

Please do not ask us to do reverse-engineering of the data your software produces. Discussion here should be primarily about Python, not reverse-engineering puzzles.

1. It should be an array, so it is a stream of blocks (array items) of the same size, right?
2. What is the exact structure of the single block? float what size, what format, endianness, padding, separators, something else?
3. b'\xcdL\x07=\xfc\x00\x00 ' … It is really hard to read binary data in the default representation of Python bytes. Please show them in hexadecimal, show the blocks and their components. Use the hex() method:

>>> b'\xcdL\x07=\xfc\x00\x00 '.hex()
'cd4c073dfc000020'

This is my python script what I tried

4. Please remove all the code not relevant to the problem (backup your file and copy the removed parts back later if needed). It is just adding distracting noise to our communication. Ideally make minimal runnable code demonstrating the problem.

I think all this should be removed (click to show):

import matplotlib.pyplot as plt

plt.ion()
fig=plt.figure()

i=0
x=list()
y=list()
i=0

5. Do you really need to close and open the serial communication? Please try to remove it. Also please test the code from my post (above) which should be better suited for the communication.

ser.close()
ser.open()

6. data = ser.readline() this expects lines (newline terminated). But you said you are sending an array (binary) so we will probably need a better suited method but we will first need to know the format of the data (points 1-3).

but I know it isn’t the right way

7. Why? What is wrong? What are the actual results? What are the expected results?