Bash, serial I/O and Arduino

Question

So, I'm in a bit over my head, and I feel like I'm very close to a solution, but it's just not working quite yet. Here's my situation:

I'm working with an Arduino microcontroller, and I'm attempting to write two Bash scripts (right now running in Mac OS X 10.6) which will (a) print all serial data coming out of the Arduino unit to the standard output, and (b) allow me to send serial data to the Arduino unit. These scripts will then be called using Adobe AIR's NativeProcess API to allow a tight integration between the Arduino unit and a Flex Adobe AIR application.

My two scripts are very simple -

Here's my WriteToSerial.sh script:

echo $1 > $2

($1 is obviously my string, $2 is the location of the serial port - currently /dev/tty.usbserial-A800eIUj)

And here's my ReadSerialOutput.sh script:

tail -f $1

($1 is the location of my serial port, currently /dev/tty.usbserial-A800eIUj)

When I call either of these scripts (or even if I just type the commands directly into the Bash console), my computer just hangs - I can type characters, but nothing happens until I Ctrl + C out of the process.

However, if I open the Arduino IDE and turn on the Serial Monitor, then tail -f the port, close the serial monitor, and then echo "test" > serial port, everything works just great.

This suggests to me that opening the Serial Monitor within the Arduino IDE is somehow initializing the serial port, which in turn allows me to tail it with no problem. This in turn suggests to me that I'm simply failing to input some sort of initialization command. However, I've been searching high and low for days and can't seem to find anything that addresses this issue.

What is the solution?

Answer 1

I get the same problem too. I use Arduino Uno with Ubuntu 12.04. After a few hours of searching and trying, I find out that Arduino will reset when the serial device is opened for the first time，but will not reset when the serial device is opened again.

So, run command - echo "input string" > /dev/ttyXXX in bash will reset Arduino and send "input string" immediately. Arduino need take some time to initialize, and is not quick enough to receive this string. cat /dev/ttyXXX will reset Arduino too.

When /dev/ttyXXX is opened in somewhere firstly, these commands will work.

Here is my solution:

1) open /dev/ttyXXX by redirecting /dev/ttyXXX to file description 3

exec 3<> /dev/ttyXXX

2) wait for Arduino's initialization

sleep 1

3) communicate with Arduino

echo "input something" >&3

cat <&3

4) close /dev/ttyXXX

exec 3>&-

Answer 2

On Linux, you need to call setserial to configure your serial port options (baud rate, parity, flow-control, etc.) before you can read/write the port correctly.

You need to find a way to do this with your Mac OS X Bash system.

Or you could write a Python script to do this.

Answer 3

I struggled with this problem also, trying no end of stty settings and tricks to cat my files to /dev/tty.usbserial-FTF7YNJ5 (in my case) whilst standing on one toe, etc.

Then I did an ls /dev and noticed /dev/cu.usbserial-FTF7YNJ5 -- oh, what's this? Apparently, a 'calling unit' version of the device that doesn't expect or provide any flow control. Dumps bytes to the port. Exactly what I needed.

So just do: cat super_file.bin > /dev/cu.usbserial-XXXXX

Hope this helps. And only now that I know the answer, I found this: http://stuffthingsandjunk.blogspot.com/2009/03/devcu-vs-devtty-osx-serial-ports.html

Answer 4

Maybe try some serial command line tool similar to serial-1.0.

See: Serial port loopback/duplex test, in Bash or C? (process substitution)