Let's Make Robots! | RobotShop

Arduino, Bluetooth, Linux

Back to work on the Ardbot. I've decided to build my control panel competely in java/JavaFX on Linux. One challenge was getting my Bluetooth connectivity going on Linux with this configuration:

  • Kensington USB Bluetooth dongle on Fedora 11 PC
  • Sparkfun  Bluetooth modem on robot

My goal will be to control the robot from a gamepad controller attached to the PC, wirelessly over the Bluetooth link.

To test the connectivity, I came up with a simple Arduino sketch that reads data from the Sharp IR range sensor and sends the distance, in centimeters, out over the wireless link, to be read by whatever program on the PC. Here is the Arduino code:

#include <NewSoftSerial.h>
 
NewSoftSerial blueSerial(11,8);
int irpin = 0;
int distance = 0;
 
void setup() {
  blueSerial.begin(9600);
}
 
void loop() {
  distance = analogRead(irpin);
  blueSerial.println(read_gp2d12_range(distance));
  delay(1000);
}
 
float read_gp2d12_range(int distance) {
  
  if (distance < 3)
    return -1; // invalid value
 
  return (6787.0 /((float)distance - 3.0)) - 4.0;

The robot is wired like this (i'm leaving out the power, gnd, etc wiring):

Arduino analog pin 0 ---> Sharp IR sensor data pin (yellow wire)

Arduino digital pin 11 ---> BT modem TX pin

Arduino digital pin 8 ---> BT modem RX pin

With the Arduino powered up, if everything is wired correctly, the red power light on the BT modem should come on.

After inserting the USB Bluetooth dongle on my PC, I ran the following commands from the linux command line to get connected:

hcitool scan 

this will give me the hardware address of the robot's BT modem - my results came back like this


Scanning ...
    01:1E:09:0F:0A:15    SparkFun-BT

To connect, I used the following command, using the hardware address from running hcitool scan:

sudo rfcomm connect 1 01:1E:09:0F:0A:15

If all is well, I should see:

Connected /dev/rfcomm1 to 01:1E:09:0F:0A:15 on channel 1
Press CTRL-C for hangup

There are a couple of ways to see the data coming across the wireless connection. The easiest way that i could think of was to run the cat command in a separate terminal window:

sudo cat /dev/rfcomm1

what do you know, i'm reading the sensor data wirelessly!

68.98
68.20
65.97
68.98
68.20
67.44

every second, the bot is sending the distance to an object in centimeters from the front mounted IR sensor.

To disconnect, from a separate terminal window run this command:

sudo rfcomm release 1

In the original window, you'll see:

Disconnected

More to follow!

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

There were a couple of us that played around with using Processing to make an interface.

I did this with one of the bluesmirf  modules and a small BT usb key on my comp.

I wasn't able to get a stable connection or at least I wasn't in the Processing app. I'd have an issue with the timing of starting the bluesmirf then  the app at around the same time to get reliable connectivity. I however had no issues when i connected to the bt device via the windows term app no special timing was required.

https://www.robotshop.com/letsmakerobots/node/6980

 

Also a curiosity on the cat command, was that reading continusously(not aware that it could do this) or was that buffered data?

Wouldn't tail -f /dev/rfcomm1 be more ideal for continuous reading?

Hi good question - i didn't try tail but maybe that would be better...cat was scrolling data down the screen and it seemed like real-time, that is i could move something in front of the sensor and the data would change...

My plan is to use the RXTX java library to hand the COM port stuff...it seems to work pretty well on Windows but haven't tried on Linux yet....

see http://www.rxtx.org/ 

Yep. thats what Processing uses for it's serial com lib.

I highly recommend checking it out.  You can also integrate java into your code. 

 

I wasn't aware that Processing was using that lib..thanks! I haven't used Processing before, but i need to check it out. I've done a lot of coding in javafx and java for my control screen, i like javafx for its ease of gui coding/animation. Perhaps Processing can do the same kind of thing...

I'd be interested to see how things work out with the rxtx lib and if it works better for you if you end up using it out of processing.

I will be keeping an eye on your updates here!

 

You are correct regarding the cat command - it was just reading data in the serial port buffer, not reading continuously - tail might work better for this kind of thing from the command line as you mentioned....

I've also noticed some weirdness in getting the RXTX lib to read from the serial port - it seems to hang every once in awhile, flushing the buffer with cat seemed to help for some reason...anyway, i'll keep posting what works and what doesn't...