Identifying serial/usb device python

Question

The solution to this problem is probably pretty simple, but I am new to interfacing with a device dynamically. What I'm doing is I am making a python executable code, so the user doesn't have to have Idle on their computer or any kind of python interpreter, which means I don't know which USB port the device will be plugged in to. The program needs to be able to open a connection to a device that is connected through a serial to usb converter. How can I determine which connected device is the correct device to open a port to? I am using pySerial to interact with the device. Any help would be greatly appreciated.

Answer 1

No matter how you configure your device, at some point you're probably going to have to ask the user where the port is, or poll all serial devices for a known response. (Polling has it's pitfalls though, so read on!). Unlike USB devices, there is no vendor/device ID that is made known to the OS when you attach a plain-old serial device.

First you need to find the serial ports. Here's a question that might help: What is the cross-platform method of enumerating serial ports in Python (including virtual ports)?.

Once you have a list of serial ports, you could ask the user whether they know which one to use. If they do, problem solved!

If they don't, you could offer to poll ALL serial devices with some data that you know will yield a certain response from your device. Keep in mind though that if the user has other serial devices attached, your string of "hello" bytes might actually be the self-destruct sequence for some other device! Hence, you should warn the user that polling may interfere with other devices, and always prompt them before you do so.

Without knowing more about your code (eg. what comms framework, if any, you're using; are you doing this in the console or are you using a GUI toolkit, etc), it's impossible to say what the best way to code this might be. In the simplest case, you could just loop over all of your serial devices, send the greeting and check for a response. (You could also do this in parallel: loop once for the greeting, and loop again to check what's in the buffer. If you're going to get more fancy than that, use a proper library.)

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Side note: You might be able to get around this if you have a built-in converter that you can set the vendor/device ID for, but the converter will still be automatically detected by any modern OS and enumerated as a serial port; you won't get to talk to it directly as a USB device. It could be possible to figure out which port goes with which ID, but I've never tried to do that. But this approach is useless if you're not the one who gets to pick the converter (eg. if it's a user-supplied cable).

Answer 2

This is the way that I used for identify Serial-USB conveter device like Arduino. It checks 'USB' String of device description.

import serial as ser
import serial.tools.list_ports as prtlst

global COMs
COMs=[]
def getCOMs():
    global COMs
    pts= prtlst.comports()

    for pt in pts:
        if 'USB' in pt[1]: #check 'USB' string in device description
            COMs.append(pt[0])

Answer 3

The only way I can think to get around the problem with probing unknown devices is to have the device send unsolicited "hello" responses continually. That was you can just connect to all serial devices and listen for the "hellos". Connecting and listening to a serial device shouldn't ever mess it up.

The downside is you have these messages cluttering up your serial stream. You could have a "I'm here now, stfu" command but then you can only connect to it once.

FTDI chips have a method of identification but you have to use their library to access the data.