Can't echo to arduino serial port unless Arduino GUI Serial Monitor open

Question

I have a rather strange issue. I DCcduino Uno (Arduino Uno copy) plugged into my Xubuntu box via the USB serial interface. Using the Arduino GUI Serial Monitor, I can communicate with the board as expected. Also, when the serial monitor is open, I can ssh into the box and run commands like echo 1700 > /dev/ttyUSB0 completely fine. However, as soon as I close the serial monitor (even if the Arduino GUI is still running) that command no longer does anything.

I have tried open the serial port with several combinations of stty arguments including everything from

stty -F /dev/ttyUSB0 9600 cs8 cread clocal

to

stty -F /dev/ttyUSB0 cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts

but it just won't write to the arduino. What am I doing wrong?

EDIT:

I just managed to get it working using

stty -F /dev/ttyUSB0 raw ispeed 9600 ospeed 9600 cs8 -ignpar -cstopb -echo
cat < /dev/ttyUSB0 > /dev/null &
echo "1700" > /dev/ttyUSB0

However, this only works with the backgrounded cat running. Is there any way to get it working without that line?

Adam893 · Accepted Answer · 2014-10-26 16:25:45Z

1

As far as I know the Arduino communicates over the serial comm port in an way that requires the connection to be present before any serial commands can be sent. I think this probably evolved as a method of preventing the AtMega chip from getting stuck waiting for commands. It also has to be compatible with the USB protocol that prevents devices from operating without a connection made.

answered Oct 26, 2014 at 16:25

Adam893

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Garrett · Accepted Answer · 2014-11-03 17:09:55Z

0

The best solution I was able to come up with was to use the pyserial library and communicate with the arduino via python, using it like a bridge between bash and the arduino. I'm sure it's just an issue with not setting the right configuration with stty but python works just fine.

answered Nov 3, 2014 at 17:09

Garrett

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