Develop Reference

Python: File Can't be Found (pySerial)

Having a small problem with opening a serial/console port via pySerial.
My program is meant to get the active com port, open a console connection and then send data. When the program is running and I plug in my RS232 USB I receive a SerialException error. (More specifically, "Could not open port: FileNotFoundError")
In the event where the program is run, it will keep printing "No RS232 Connected", but when the RS232 USB is connected the program breaks and runs into the SerialException error.
If I plug in the RS232 USB before running the program and then run it, it reads and performs normal operation without issue.
ports = serial.tools.list_ports.comports(include_links=False)
if not ports:
print("No RS232 Connected")
if ports:
for port in ports:
print('Found port ' + port.device)
ser = serial.Serial(port.device)
if ser.isOpen():
ser.close()
break
console = serial.Serial(port.device, baudrate=9600, parity="N", stopbits=1, bytesize=8, timeout=0.4)
I am quite new to Python and programming in general, but I feel that the problem may be around the 'ports' list already being populated twice due to the while True loop. Then when we go to create the console by opening the port we are expecting one entry in the list, but there are two.
Since we can't have 2 open console connections on the same COM port, we receive the error.
If I print the 'ports' list I get this.
"[<serial.tools.list_ports_common.ListPortInfo object at 0x000002B5D77F0D68>]
[<serial.tools.list_ports_common.ListPortInfo object at 0x000002B5D77F0D68>]"
Any help would be greatly appreciated! Please let me know if you require any more details.
Thanks,

After further research into it, I have realised that when a RS232 USB is plugged into the PC, we need to give it a bit of time to open a stream. It sounds like it is opened when the temp file is created for it.
Although it was identifying that a COM port was available almost immediately, it was not ready by the time I was trying to create the Serial instance, which was why I was getting the FileNotFound error.
A simple sleep function of half a second has solved the issue!

Problem communicating with Xiaomi M365 using a serial port in a Raspberry

I'm trying to communnicate with a Xiaomi M365 scooter using a serial port connected to a Raspberry Pi in the port /dev/ttyUSB0. To test it I'm using Python scripts, for example, in this one I'm trying to execute a command to turn on the rear light:
import serial
import time
with serial.Serial('/dev/ttyUSB0',
baudrate = 115200,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS,
timeout=1) as ser:
time.sleep(1);
ser.write("55aa0320037d025aff".decode('hex'));
The problem is that sometimes it works and sometimes not, it can take me up to 10 executions to actually turn on the light, this also occurs with any other command like the one to turn off the rear light or the one to get the scooter's data.
I think the problem could be related with the way that the data is written to the serial port in the Raspberry, or how the Raspberry manage the serial port, but although I have been searching for days I cannot find how to fix it.
Just to give more info about the issue, if I connect the USB, connected to the Xiaomi M365, to a machine with windows, instead to a Raspberry, everything works as expected always.
Thanks a lot in advance for your support.
Best regards.

Pyserial write() hangs

I need to communicate with some device using serial port. I know this device parameters (boudrate etc.). I also know that this device waits untill it receives a new line character (I don't know unix or windows type) and then sends back something in ASCII.
The problem is that when i want to write anything the script hangs. No error occurs, just nothing happens later. It's impossible to print anything or even to close the port.
How can I fix that?
It doesn't work for really basic script. Of course this is no a whole code, just an example to present what is not working.
Sadly, I didn't find any explanation or an answer which works.
I'm working on Ubuntu 16.04
Thanks for your help!
import serial
ser = serial.Serial(
port="/dev/NameOfDevice",
baudrate=115200,
bytesize=8,
parity='N',
stopbits=1,
timeout = 0)
ser.open()
print('Port was opened')
ser.write(b'\r\n') #this is a line where it stops working. Different inputs were tried, nothing works.
print('Does it works?')

edit: I was a fool before, but now I am certain I am correct.
I ran into the same problem and solved it by adding a "write_timeout":
ser = serial.Serial(
port="/dev/NameOfDevice",
baudrate=115200,
bytesize=8,
parity='N',
stopbits=1,
write_timeout = 1,
timeout = 0)
Note that this will raise a timeout exception. In my case this is the expected behavior, because I'm checking to see if I can properly connect on the user specified port.
So I suspect you are connecting to something, but it isn't acknowledging your write, and since the default behavior for 'write' is to block until acknowledgement, this is what you see.
See also the api description for the write function:
https://pyserial.readthedocs.io/en/latest/pyserial_api.html

python serial write timeout

I have used pyserial for a couple of days. However, a problem occurs today. I met serial write timeout. Several days before, when I used a switch, everything is OK. But today I changed for another switch. Then serial write timeout appears. I did not change any code, but the problem is actually quite severe. More seriously, the timeout not always occurs, which means that sometimes I can write in the serial successfully.
ser = serial.Serial( #Serial COM configuration
port='COM5',
baudrate=9600,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS,
rtscts=True,
timeout=2,
writeTimeout=5
)
strInput = "show ver"
ser.flushInput()
ser.flushOutput()
ser.write(strInput.encode('utf-8')+b'\n')
I have ensured that the port is COM5 and the baudrate of the switch is 9600. Thanks a lot for answering my question.

I ran into this problem recently. I found that setting write_timeout=0 solved the issue (also, not really sure why a write timeout even exists...)
Another answer here suggests the same thing :)

If you have flow control with request to send / clear to send structure and the device you are writing to isn't responding you need the timeout for the write in order to not hang

The problem may be that the interface tries to comply with RTS, CTS, DSR, or DTS signals. It is possible that if they are not properly connected, they can mysteriously affect communication through a timeout.
One solution may be to ignore their influence using rtscts=False and/or dsrdtr=False when opening the serial port in Python.

Python Serial Port - unable to write data

I am relatively new to Python. I wrote a script and need to add triggers that need to be send via an usb serial port to another pc. The problem is that the triggers (in this code example the 2) never show up on the software on the other pc. When I check it with the print() command, it does print a value, but the printed value is the same number for two different triggers. I have read other posts, I searched the internet, and I tried various things, but I didn't manage to resolve this iusse. This is the code I use for interfacing with the serial port (COM3).
#this part of code is defined at the beginning:
import serial
ser = serial.Serial(port=2, baudrate=9600)
ser.close()
#this part of the code later on to interface with the serial port:
ser.open()
ser.write(chr(2))
ser.close()
Maybe anyone here has any suggestions on where the problem could be? Thanks!

If you haven't already, check that the port settings are correct, 9600,8,N,1 for example. These must match the settings of the remote serial port.
It might be useful to check that the serial connection does work with a terminal emulation program such as minicom (linux), or PuTTY (Windows). Once you have verified that a connection can be made and data transferred, you can be certain that you are connecting to the correct local port, that the port settings are correct, and that your serial cable is working properly.