Failing to get response from serial port using pyserial

Question

I'm trying to connect to a device using a serial port. I tried two ways – 1) pyserial in Python and 2) PuTTY. I managed to connect to the device and use it, using PuTTY. However, in Python I can only connect to the device (open the port) but I fail to send commands or read the port.

Note that I'm using exactly the same settings in both my Python script (below) and PuTTY settings. But perhaps I'm missing something. How do I fix my script?

My Python code (I'm using Windows 11):

import serial
import time


def send_command_to_com_port(ser, command):
    try:
        # Send the command
        command_encoded = command.encode('ascii')
        ser.write(command_encoded)
        print(command_encoded)

    except serial.SerialException as e:
        print(f"Error communicating with the COM port: {e}")


def read_from_com_port(ser):
    try:
        # Read response from the COM port
        response = ser.read_until("\n")  # Read until a newline character is encountered
        if response:
            print(f"Response received: {response.decode('ascii').strip()}")
        else:
            print("No response received from the COM port.")

    except serial.SerialException as e:
        print(f"Error communicating with the COM port: {e}")


# Specify the COM port and send the command
com_port = "COM4"

# Configure the serial connection
ser = serial.Serial(
    port=com_port,  # Replace with your COM port (e.g., 'COM3' on Windows or '/dev/ttyUSB0' on Linux)
    baudrate=115200,  # Baud rate
    bytesize=serial.EIGHTBITS,  # 8 data bits
    parity=serial.PARITY_NONE,  # No parity bit
    stopbits=serial.STOPBITS_ONE,  # One stop bit
    timeout=1  # Timeout in seconds
)

# Ensure the COM port is open
print(f"Serial port opened: {ser.is_open}")

# Send commands to the COM port
send_command_to_com_port(ser, 'm0\n')
time.sleep(2)
read_from_com_port(ser)

# Close the serial port
ser.close()
print("Serial connection closed.")

The output I get using the code above is always:

Serial port opened: True
b'm0\n'
No response received from the COM port.
Serial connection closed.

Process finished with exit code 0

Additional note: All instructions to the device must be ascii encoded and must end with a newline character '\n'.

After sending the command m0 I should receive a confirmation as a string. But I get nothing.

Answer 1

Found a solution!

The issue was that the device did not have enough time to react to the initial command after opening of the COM port. I put time.sleep(2) after creating Serial object and everything works as it should.