How to setup serial communication in Processing to /dev/rfcomm0 - bluetooth

Question

I am trying to perform serial communication on between Ubuntu 12.04 and a JY-MCU bluetooth serial module connected to an Arduino.
I have created this configuration in /etc/bluetooth/rfcomm.conf
rfcomm0 {
# # Automatically bind the device at startup
bind yes;
#
# # Bluetooth address of the device
device 00:12:11:19:08:54
# # RFCOMM channel for the connection
channel 1;
# # Description of the connection
comment "Linvor Bluetooth Module";
}
I can use putty to communicate with the /dev/rfcomm0 serial port and this works perfectly.
However, despite many attempts I simply cannot see how to create a serial port in Processing that works in any way.
For example :
println(Serial.list());
prints nothing at all.
If I execute:
String portName = "/dev/rfcomm0";
myPort = new Serial(this, portName, 9600);
println(myPort);
I see this in the monitor:
processing.serial.Serial#1712651
But if I then call:
myPort.write('9');
I get an exception:
java.lang.NullPointerException
at processing.serial.Serial.write(Serial.java:572)
...
I can't understand why this fails. I have been following all the instructions from Tom Igoe's "Making Things Talk", but this just does not work the way he says...
Any help would b great!
Thanks,
Bob

Answer 1

Aftert searching high and low, I have made this work.
The key issue is that processing uses the rxtx java library (RXTX-2.1-7) for serial communications.
The RXTX wiki says:
"rxtx tries to detect ports on by scanning /dev for files matching any
of a set of known-good prefixes, such as 'ttyS', 'ttym', and since 2.2
'ttyUSB' and so on. "
And since the bluetooth device is named rfcomm* it cannot be detected.
The trick is to create a sym link to fool rxtx (use a ttyS device that is not yet assigned):
$ sudo ln -s /dev/rfcomm0 /dev/ttyS99
Then, connect:
$ sudo rfcomm connect 0
Connected /dev/rfcomm0 to 00:12:11:19:08:54 on channel 1
Press CTRL-C for hangup
At this point the red led on the JY-MCU becomes solid and processing can detect it:
println(Serial.list());
output is:
[0] "/dev/ttyACM0"
[1] "/dev/ttyS99"
So, serial communication can work.
To summarize, the following process will allow a processing script to communicate via a serial port with a JY-MCU device in a BlueZ linux framework
One time setup:
power up the JY-MCU,
use the following command to get its hardware address, mine is 00:12:11:19:08:54
$ hcitool scan
use that to create the /etc/bluetooth/rfcomm.conf file; you'll note that I chose 0 for the rfcomm device , we need that for connection later:
$ cat /etc/bluetooth/rfcomm.conf
rfcomm0 {
bind yes;
device 00:12:11:19:08:54;
channel 1;
comment "Linvor Bluetooth Module";
}
use BlueMan to pair the JY-MCU.
Every time you want to use the JY-MCU
create the sym link:
$ sudo ln -s /dev/rfcomm0 /dev/ttyS99
connect to the JY-MCU:
$ sudo rfcomm connect 0
Connected /dev/rfcomm0 to 00:12:11:19:08:54 on channel 1
Press CTRL-C for hangup
you can now run a processing script and connect to the JY-MCU with
the code:
String portName = "/dev/ttyS99";
myPort = new Serial(this, portName, 9600);
after running the processing script, be sure to CTRL-C at the
command line to disconnect the JY-MCU.
That should do it!
Ciao,
Bob

Answer 2

Just something popped up in my mind.
I had similar problems that were caused due to channel 1 is already used. If you bind to a channel which already is in use, bad things may happen.
sdptool browse local
Use that command to see which channels are available on your Ubuntu device.