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PhD Student in ECE @ MSU

Use CH340-based USB Serial Converter on Linux in Python

2018-04-26

CH340 is a chip that convert USB data to serial data. Of cause the method discuss here can be applied to other USB-serial converter chips, such as PL2303 etc. It is helpful when you want to do serial communication with your circuit board. Usually I write Python scripts to interact with serial devices.

Find the Device

In your terminal, run

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lsusb

If your device is plugged, you can see an item about it. If not, make sure your circuit board is functioning well.

Next, run

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dmesg | grep ttyUSB

Usually the name should be something like ttyUSB0.

Change Your Permission

Use chmod to change device access permission.

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sudo chmod 777 /dev/ttyUSBx

(replace the ‘x’ with your device number.)

Try to Open the Serial Port in Python

In python script, use pyserial library to handle the serial devices.

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import pyserial

ser = serial.Serial('/dev/ttyUSB0', '9600', timeout=2)
ser.write('your command\r\n'.encode('ascii'))  # convert to ASCII before sending it
buf = ser.read(100)  # read 100 bytes

print(buf.decode('utf-8'))

Basically this is how it works.

Note: On Windows, the /dev/ttyUSB0 string should usually be COM0 etc. That’s the difference.



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