How to read and write from a COM Port using PySerial?

10
votes

I have Python 3.6.1 and PySerial Installed. I am trying the

I am able to get the list of comports connected. I now want to be able to send data to the COM port and receive responses back. How can I do that? I am not sure of the command to try next.

Code:

import serial.tools.list_ports as port_list
ports = list(port_list.comports())
for p in ports:
    print (p)

Output:

COM7 - Prolific USB-to-Serial Comm Port (COM7)

COM1 - Communications Port (COM1)

I see from the PySerial Documentation that the way to open a COM Port is as below:

import serial

>>> ser = serial.Serial('/dev/ttyUSB0')  # open serial port

>>> print(ser.name)         # check which port was really used

>>> ser.write(b'hello')     # write a string

>>> ser.close()             # close port

I am running on Windows and I get an error for the following line:

ser = serial.Serial('/dev/ttyUSB0')

This is because '/dev/ttyUSB0' makes no sense in Windows. What can I do in Windows?

2
pythonpyserial
Yes, silly me. Should have researched a bit. I can mark yours as an answer if you answer. – Neil Dey
It's ok to ask for help like that when you've at least tried it as you did :) – pointerless
Can you please keep that link shared to that you had earlier? – Neil Dey
Its in my answer – pointerless

2 Answers

11
votes

This could be what you want. I'll have a look at the docs on writing. In windows use COM1 and COM2 etc without /dev/tty/ as that is for unix based systems. To read just use s.read() which waits for data, to write use s.write().

import serial

s = serial.Serial('COM7')
res = s.read()
print(res)

you may need to decode in to get integer values if thats whats being sent.

2
votes

On Windows, you need to install pyserial by running

pip install pyserial

then your code would be

import serial
import time

serialPort = serial.Serial(
    port="COM4", baudrate=9600, bytesize=8, timeout=2, stopbits=serial.STOPBITS_ONE
)
serialString = ""  # Used to hold data coming over UART
while 1:
    # Wait until there is data waiting in the serial buffer
    if serialPort.in_waiting > 0:

        # Read data out of the buffer until a carraige return / new line is found
        serialString = serialPort.readline()

        # Print the contents of the serial data
        try:
            print(serialString.decode("Ascii"))
        except:
            pass

to write data to the port use the following method

serialPort.write(b"Hi How are you \r\n")

note:b"" indicate that you are sending bytes