Python Forum

Hello,

I'm using a function ser.read (from PySerial) to read a sequence of 2000 bytes from a microcontroller. Two received bytes in a sequence are actually two bytes of uint16 data which are combined in python script (so in Python these sequence of 2000 bytes are combined into 1000 uint16_t data), but that's not important here.

I have a problem with understanding the received bytes of ser.read form the figure bellow (print(s))? Please click the the gray rectangle bellow to see the figure.

[attachment=1672]


After printing out data received with ser.read with print(s) I can see strange printout. I would expect that each byte is in a form like \x04, but at the beginning I can see the form like \x04J, the listing also start with G\04F\...? So at the beginning of the figure I can see that there are three numbers or a strange (not hex) characters instead of two hex numbers (equals one byte)?

The code is here:

import serial
import numpy as np
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.widgets import Slider, Button, RadioButtons
from scipy.signal import savgol_filter

import matplotlib.pyplot as plt
from pylab import *
import numpy as np

ser = serial.Serial('COM13', 921600, timeout=None,parity=serial.PARITY_NONE)
fig = plt.figure()


while True:

    ser.flush()

    x = np.linspace(0, 1000, 1000)

    s = ser.read(2000)
    y1 = np.frombuffer(s, np.uint16)  #y ... np array...
    
    plt.plot(x,y1,'-*',label='graf 1')  

    plt.xlabel('TIME')
    plt.ylabel('ADC current')
    plt.title('Solenoid I/t')

    legend()

    plt.show()

    print(s)

ser.close()             # close port

I will be grateful for any help
Ernest

can you find any help here: https://github.com/pyserial/pyserial/tre...r/examples ?

This is because Python shows bytes corresponding to printable ascii characters as characters, as well as the escape sequences \t \n \r

>>> bytes(range(256))
b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>> for i in range(16):
...     print(bytes(range(16 * i, 16 * i + 16)))
... 
b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'
b'\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f'
b' !"#$%&\'()*+,-./'
b'0123456789:;<=>?'
b'@ABCDEFGHIJKLMNO'
b'PQRSTUVWXYZ[\\]^_'
b'`abcdefghijklmno'
b'pqrstuvwxyz{|}~\x7f'
b'\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f'
b'\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f'
b'\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf'
b'\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf'
b'\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf'
b'\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf'
b'\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef'
b'\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>> 

so G is \x47 and F is \x46 for example.

Thank you very much!
Ernest