Bash, serial I/O and Arduino

26
votes

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?

10
bashcommand-lineserial-portarduino
I should add - I've tried using "stty -F /dev/tty.usbserial-XXXXX" but I get "stty: illegal option -- -F" - which doesn't sound right to me. – Myk
OK, so now I've learned that -F and --file for some reason don't work in my OS but that "-f" works - so I do that, and still no dice. – Myk
You might want to ask this question on electronics.stackexchange.com, they deal with questions related to Arduinos and embedded programming. – J. Polfer
Since tail is always running till last line, which will not appear until serial bus is closed, found head rather useful head --lines 1 < /dev/ttyUSB0 – McPeppr

10 Answers

14
votes

Try using the tool stty:

stty -F /dev/my_serial_port <baud_rate> cs8 cread clocal

As always, read the manpage before applying the above. cread allows you to receive data. You may want to omit clocal if you are using flow control. If you aren't sure what the above settings are, ask, and I can write up a more complete answer.

32
votes

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>&-

4
votes

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

2
votes

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.

1
votes

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

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

0
votes

Try adding an ampersand (&) to the end of the commands to put the process in the background. If the console is hanging up, then that means the script or process is still running on your current terminal, and you won't be able to input or click on anything until the process or script is done.

You can also try running the command in 1 terminal window, and open a new terminal window/tab, and try tailing from there.

0
votes

Check to see if sending data to / receiving data from the Arduino unit is working by using a different app such as Cornflake (serial terminal for Mac OS X) - instead of using the Arduino IDE & the Serial Monitor.

In addition, you may want to check out if you could benefit from switching to Xcode (in terms of debugging features, etc.).

See: Setting up Xcode to Compile & Upload to an Arduino ATMega328 (Duemilanove)

0
votes

There's also Apple's SerialPortSample command line tool that allows you to set arbitrary baud rates:

// from: SerialPortSample/SerialPortSample.c
// ...
// Starting with Tiger, the IOSSIOSPEED ioctl can be used to set arbitrary baud rates
// other than those specified by POSIX. The driver for the underlying serial hardware
// ultimately determines which baud rates can be used. This ioctl sets both the input
// and output speed. 
// ...

For more information see: http://www.arduino.cc/playground/Interfacing/Cocoa

Another piece of Cocoa sample code that shows you how to talk to the Arduino microcontroller over a serial connection is objective-candarduino (hosted on Google code).

0
votes

A one-liner Something that works really well for datalogging, and acting on data:

  • monitoring: the arduino output can trigger actions on the computer
  • data-logging: it simultaneously save that streaming data to a file
  • notchecked? sending-messages: I haven't tried sending data yet to the arduino, but see the second example, might be able to send a message to the serial port via some cmdline util.

the following timestamps and sends to stdout

cat /dev/cu.usbmodem1421 | awk '{ for (i=0; i<NF; i++) printf $i + system("echo  , `date`")}'

Sample Output:

enter image description here

This method can even be adapted to monitor and act upon the data in real time:

cat /dev/cu.usbmodem1421 | awk '{ for (i=0; i<NF; i++) printf $i + system("echo , `date`)}'

more examples here: https://github.com/gskielian/Arduino-DataLogging/tree/master/Bash-One-Liner