Arduino and Python communication errors

Question

Background: I am working on a project that is supposed to have an Arduino mega send data from ultra sonic sensors to the computer via USB and I keep getting the same errors. I have checked the device manager and I am sure that the Arduino is on the correct port.

My python errors:

Traceback (most recent call last):
File "----", line 6, in <module>
ser = serial.Serial('COM4', 115200)
File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 38, in __init__
SerialBase.__init__(self, *args, **kwargs)
File "C:\Python27\lib\site-packages\serial\serialutil.py", line 282, in __init__
self.open()
File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 66, in open
raise SerialException("could not open port %r: %r" % (self.portstr, ctypes.WinError()))
serial.serialutil.SerialException: could not open port 'COM4': WindowsError(5, 'Access is denied.')
[Finished in 0.1s]

My Arduino error:

[Stino - Start building "---"...]
Sketch uses 4,922 bytes (1.9%) of program storage space. Maximum is 258,048 bytes.
Global variables use 727 bytes (8.9%) of dynamic memory, leaving 7,469 bytes for local variables. Maximum is 8,196 bytes.
[Stino - Done building "----" in 0.1s.]
[Stino - Start uploading...]
avrdude: ser_open(): can't open device "\\.\COM4": Access is denied.
avrdude: ser_drain(): read error: The handle is invalid.
[Stino - Exit with error code 1.]

I have been working at this for awhile now and I still do not understand how to fix this. Please help.

Eugene Sh. · Accepted Answer · 2015-02-23 18:54:36Z

3

The error is very basic here. Your arduino COM port is not COM4. You can see this by the fact you are not even able to upload your program. Inspect the Ports section in your Device Manager to find out which is the right one.
Upd: Or if it is COM4, as suggested in the other answer, it is opened by some other program. It can be another Arduino IDE or your previously ran python program attempts that are still in the memory. Check the task manager in order to find and kill the suspects.

edited Feb 23, 2015 at 18:54

answered Feb 23, 2015 at 18:31

Eugene Sh.

18.7k8 gold badges45 silver badges69 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Fordro47 Over a year ago

Like I said above it is COM4. I just checked it again.

Fordro47 Over a year ago

Found that my python was still executing and I didn't realize. Thanks!

Robert McMurry · Accepted Answer · 2015-02-23 18:36:32Z

2

A common cause for this kind of error, if you are sure "COM4" is correct, is that another program currently is using the port and not allowing python to access it. Close any other programs trying to talk to the arduino on COM4 and try again.

answered Feb 23, 2015 at 18:36

Robert McMurry

314 bronze badges

1 Comment

Fordro47 Over a year ago

The only programs that I have running are Sublime 3 and Chrome. So I don't think that is the problem.

Collectives™ on Stack Overflow

Arduino and Python communication errors

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related