Linux and Python: auto-detect Arduino serial port

Question

I have a problem automagically detecting my Arduino's serial port in Python, using Mac/Linux.

I know a working shell command to find the port; because Arduino serial ports almost always begin with tty.usbmodem, you can find the serial port with ls /dev | grep tty.usbmodem which should return something like tty.usbmodem262141.

However, I'm confused on how to call this shell command from my Python code. I've tried this:

p = "/dev/" + str(subprocess.Popen('ls /dev | grep tty.usbmodem', shell=True).stdout)

Which should make p become /dev/tty.usbmodem262141.

However, at the moment I get /dev/None.

How can I modify my shell script call to return the right string? I've tried to use several commands to call shell scripts, but none have worked.

score 8 · Accepted Answer · answered Jul 06 '12 at 15:16

8

First of all, if you're using a shell, you can use a glob (*), so your command would become ls /dev/tty.usbmodem*.

Next, you don't even have to call a shell command to use a glob in Python!

Consider the following code:

import glob

print(glob.glob("/dev/tty.usbmodem*"))

answered Jul 06 '12 at 15:16

cha0site

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Hmm, I must be doing something wrong... I tried the code and got back an empty list `[]`. – hao_maike Jul 06 '12 at 15:19
2

@mr_schlomo: You sure you have these `tty.usbmodem` files? – cha0site Jul 06 '12 at 15:24
ooops--my Arduino was disconnected! thanks for the help! – hao_maike Jul 06 '12 at 15:24
Is it possible to find an arduino on Windows similarly? – Tim Sep 14 '12 at 22:32

score 2 · Answer 2 · answered Jul 25 '12 at 04:14

I wrote this to find out what dev the arduino was plugged into on osx 10.7.x : enjoy.

#!/usr/bin/env bash

# script name: findtty.sh
# author: Jerry Davis
#
# this little script determines what usb tty was just plugged in
# on osx especially, there is no utility that just displays what the usb
# ports are connected to each device.
#
# I named this script findtty.sh
# if run interactively, then it prompts you to connect the cable and either press enter or   it will timeout after 10 secs.
# if you set up an alias to have it run non-interactively, then it will just sleep for 10 secs.
# either way, this script gives you 10 seconds to plug in your device

# if run non interactively, a variable named MCPUTTY will be exported, this would be an advantage.
# it WAS an advantage to me, otherwise this would have been a 4 line script. :)
#
# to set up an alias to run non-interactively, do this:
#   osx: $ alias findtty='source findtty.sh',
#   or linux: $ alias findtty='. findtty.sh' (although source might still work)

\ls -1 /dev/tty* > before.tty.list

if [ -z "$PS1" ]; then
    read -s -n1 -t 10 -p "Connect cable, press Enter: " keypress
    echo
else
    sleep 10
fi

\ls -1 /dev/tty* > after.tty.list

ftty=$(diff before.tty.list after.tty.list 2> /dev/null | grep '>' | sed 's/> //')
echo $ftty
rm -f before.tty.list after.tty.list
export MCPUTTY=$ftty                     # this will have no effect if running interactively

score 0 · Answer 3 · answered Jul 31 '12 at 20:31

I've used this code to auto detect serial ports on linux. Its based on some code I found in the MAVLINK project.

import fnmatch
import serial

def auto_detect_serial_unix(preferred_list=['*']):
    '''try to auto-detect serial ports on win32'''
    import glob
    glist = glob.glob('/dev/ttyUSB*') + glob.glob('/dev/ttyACM*')
    ret = []

    # try preferred ones first
    for d in glist:
        for preferred in preferred_list:
            if fnmatch.fnmatch(d, preferred):
                ret.append(d)
    if len(ret) > 0:
        return ret
    # now the rest
    for d in glist:
        ret.append(d)
    return ret

def main():
    available_ports = auto_detect_serial_unix()
    port = serial.Serial(available_ports[0], 115200,timeout=1)
    return 0

if __name__ == '__main__':
    main()

score 0 · Answer 4 · answered Oct 17 '12 at 00:25

Another way of solving this if you want a purely shell solution is to use a combination of 'ls' and awk which I have found handy for all kinds of niche applications.

First plug in your Arduino and make sure it shows up when you do

ls /dev/tty*

crw-rw---- 1 root dialout 166, 0 2012-10-16 18:37 /dev/ttyACM0

My Arduino Uno shows up as a ttyACM* so I modified the command to be more selective and then piped the output to awk which can then print space delimited fields very easily.

ls /dev/ttyACM* | awk {'print $9'}

/dev/ttyACM0

You will still have to do something with the final output such as export it to use in the shell or send to a file for later reading.

Linux and Python: auto-detect Arduino serial port

4 Answers4

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