Troubleshooting python serial communication

Question

I am trying to use a python script to control a rotating valve. I am able to do so through PuTTY but not using my script. Code is shown below. I also included PuTTY settings and a link to the valve positioner user manual that gives example commands.

import serial
ser = serial.Serial()
ser.port = 'COM7'
ser.baudrate = 9600
ser.bytesize = serial.SEVENBITS
ser.parity = serial.PARITY_ODD
ser.xonxoff = 0
ser.rtscts = 0
ser.dsrdtr = 0
ser.stopbits = 1
ser.timeout = 1
ser.open()
if ser.isOpen():
 print(ser.name + ' is open...')
 while True:
 cmd = input("Enter command or 'exit':")
 if cmd == 'exit':
 ser.close()
 break
 else:
 # ser.write(cmd.encode('ascii'))
 # ser.write(bytes(cmd, 'utf-8'))
 ser.write(str.encode(cmd))
 out = ser.readline()
 print('Receiving... ' + str(out))

PuTTY Settings 1

PuTTY Settings 2

User Manual

PuTTY Settings 3

• quamrana: Did you mean to send: cmd + '\n'?
• PCT: Is that necessary? I just tried it and it didn't resolve the issue
• quamrana: The manual mentions the command ending in <CR>
• DaveL17: Have you tried running the Python script against COM1 to see if that makes a difference?
• quamrana: You could also try cmd + '\r\n' to make it the same as the PUTTY setting of Implicit LF in every CR

Answer 1

The manual that you link to says that it needs a <CR> at the end of each command.

Also your putty configuration says that it adds crlf.

You could change your code like this:

ser.write(str.encode(cmd + '\r\n'))