Linux - Serial Communication with RS485

Question

I have been trying to send the bytes (in order): 2201 , 2211 etc. to my Arduino board, which I've connected to my computer, using a USB to RS485 adapter.

However, when I connect it yo my computer, whenever I try to send 2201 to my Arduino, using the command echo 2 > /dev/ttyUSB0;echo 2 > /dev/ttyUSB0;echo 0 > /dev/ttyUSB0;echo 1 > /dev/ttyUSB0 , it sometimes works, turning the LED on normally as it should, but other times it just doesn't, displaying bash: /dev/ttyUSB0: Input/output error .

If you have any way of getting through this, that'd be great. Also, please let me know if there's any better command than echo X > /dev/ttyUSB0 to send data to my Arduino. I'm new to serial communication, so I'm not sure what the best way to do this is.

Answer 1

First, a question: why are you using multiple echo statements, rather than a single echo 2201 > /dev/ttyUSB0 ? The latter requires substantially less typing.

A problem with both your solution and the one I just proposed is that the echo command appends a newline to its output. So if I were to direct output to a file; like this:

echo 2 >afile; echo 2 >>afile; echo 0 >>afile; echo 1 >>afile

I end up with a file that contains:

2\n2\n0\n1\n

And that's exactly what you're sending out the serial port. You can use the -n option to echo to suppress newline, so:

echo -n 2201 > /dev/ttyUSB0

You would probably be better off using something other than the shell to interact with serial ports. Python (with the pyserial module) is a good choice, but so is just about anything else. If you do keep using the shell, there are some other stackexchange questions worth looking at, such as this one and this one .

If you want to have interactive access to the serial port, there are a number of common applications that can help out with that (screen, ckermit, picocom, moserial, minicom, etc).