Tag Archives: code

Arduino Micro /Leonardo and rosserial Hello World possible link problem?

Yesterday I’ve had to learn something the hard way. Please have a look at the following code of the rosserial “hello world” arduino example:

/*
 * rosserial Publisher Example
 * Prints "hello world!"
 */

#include <ros.h>
#include <std_msgs/String.h>

ros::NodeHandle  nh;

std_msgs::String str_msg;
ros::Publisher chatter("chatter", &str_msg);

char hello[13] = "hello world!";

void setup()
{
  nh.initNode();
  nh.advertise(chatter);
}

void loop()
{
  str_msg.data = hello;
  chatter.publish( &str_msg );
  nh.spinOnce();
  delay(1000);
}

Nothing special, right? So compiling it – uploading everything on the arduino works like a charm.

But starting it  rosrun rosserial_python serial_node.py /dev/ttyACM0 crashes with:

rosrun rosserial_python serial_node.py /dev/ttyACM0
[INFO] [WallTime: 1400737593.278250] ROS Serial Python Node
[INFO] [WallTime: 1400737595.610358] Connecting to /dev/ttyACM0 at 57600 baud
/home/yourUser/catkin_ws/src/rosserial/rosserial_python/src/rosserial_python/SerialClient.py:317: SyntaxWarning: The publisher should be created with an explicit keyword argument 'queue_size'. Please see http://wiki.ros.org/rospy/Overview/Publishers%20and%20Subscribers for more information.
  self.pub_diagnostics = rospy.Publisher('/diagnostics', diagnostic_msgs.msg.DiagnosticArray)
[ERROR] [WallTime: 1400737595.826375] Error opening serial: could not open port /dev/ttyACM0: [Errno 13] Permission denied: '/dev/ttyACM0'

which can be easily explained by normal users missing permission to access the /dev/ttyACM0. So I advice running it as root, which leads you to customize roots .bashrc including the source /home/yourUser/yourWorkspacePath/devel/setup.bash and the environment variables like ROS_HOSTNAME and ROS_MASTER.

So after that, running it again with root permissions, you’ll get another error message:

[INFO] [WallTime: 1400737809.741920] ROS Serial Python Node
[INFO] [WallTime: 1400737810.415142] Connecting to /dev/ttyACM0 at 57600 baud
/home/yourUser/catkin_ws/src/rosserial/rosserial_python/src/rosserial_python/SerialClient.py:317: SyntaxWarning: The publisher should be created with an explicit keyword argument 'queue_size'. Please see http://wiki.ros.org/rospy/Overview/Publishers%20and%20Subscribers for more information.
  self.pub_diagnostics = rospy.Publisher('/diagnostics', diagnostic_msgs.msg.DiagnosticArray)
[ERROR] [WallTime: 1400737827.716961] Unable to sync with device; possible link problem or link software version mismatch such as hydro rosserial_python with groovy Arduino

So – rosserial tries to connect to your /dev/ttyACM0 using 57600 baud and fails. The error message is kind of misleading – of course there is some syncing issue, and it has nothing to do with your ROS version… …but with your arduino!

Since the arduino micro / leonardo uses USB for and its build in serial-controller both for programming and communicating, rosserial needs the information to access the device not in the for arduino usual serial way but with USB. So simply adding

#define USE_USBCON

before the rest of the code, will tell ROS to do so.

 

 

Howto control CubieTruck onboard LEDs

Today I wanted to know, what this little blinking lights on my [amazon &title=CubieTruck&text=CubieTruck] mean.

There are four, which you find out if you use:

root@cubietruck:/# ls /sys/class/leds/

blue:ph21:led1 green:ph07:led4 orange:ph20:led2 white:ph11:led3

(or just look at it while it is running, usually it blinks a lot)

IMG_20140520_123004

So if you want to know what each blink means you can ask the [amazon &title=CubieTruck&text=CubieTruck] like that:

root@cubietruck:cd /sys/class/leds/
root@cubietruck:/sys/class/leds# ls
blue:ph21:led1  green:ph07:led4  orange:ph20:led2  white:ph11:led3
root@cubietruck:/sys/class/leds# cat green:ph07:led4/trigger
none rfkill0 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid ac-online usb-online [mmc0] mmc1 timer heartbeat cpu0 cpu1 default-on rfkill1 rfkill2 
root@cubietruck:/sys/class/leds# cat blue:ph21:led1/trigger
none rfkill0 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid ac-online usb-online mmc0 mmc1 timer [heartbeat] cpu0 cpu1 default-on rfkill1 rfkill2 
root@cubietruck:/sys/class/leds# cat orange:ph20:led2/trigger
none rfkill0 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid ac-online usb-online mmc0 mmc1 timer heartbeat [cpu0] cpu1 default-on rfkill1 rfkill2 
root@cubietruck:/sys/class/leds# cat white:ph11:led3/trigger
none rfkill0 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid ac-online usb-online mmc0 mmc1 timer heartbeat cpu0 [cpu1] default-on rfkill1 rfkill2 

So by default the

  • green LED is indicating if there is any read write with the SD Card
  • blue LED is heartbeating
  • orange LED is CPU0 load
  • white LED is CPU1 load

In case you want to turn off the LEDS, use this code:

# turn off LEDs
echo 0 > /sys/class/leds/blue:ph21:led1/brightness
echo 0 > /sys/class/leds/green:ph07:led4/brightness
echo 0 > /sys/class/leds/white:ph11:led3/brightness
echo 0 > /sys/class/leds/orange:ph20:led2/brightness

See here for more information.

Howto run a 12V bipolar stepper motor with arduino micro and L298N at 150rpm

Today I experimented with a 12V bipolar stepper motor and the 5V arduino micro.

To get things working I’ve put the 9V from my six 1.5V Batteries into an UBEC which accelerates them to 12V at a loss of below 10% (at 350mAh) connected them to the VCC of the L298N and wired the 4 signal cables of the motors to it. Because thats a lot of numbers to keep track of – I’ve made a small video of the setup:

Doing the math according to a wheel with 5,8cm heigth and 150rpm I’ve reached, my robot will be able to run about 1,6 km/h – this might be increased with a better motor driver like they used on the arduino motor shield. I’ve read they reached about 250 rpm on the same motor which would be 2,73km/h.

The code of the arduino is pretty simple:

#include <Stepper.h>

const int stepsPerRevolution = 200;  // change this to fit the number of steps per revolution
// for your motor


// init the stepper lib on pins 8 through 11:
Stepper myStepper(stepsPerRevolution, 8,9,10,11);            

void setup() {
  // nothing to do inside the setup
}

void loop() {
    myStepper.setSpeed(150);
    myStepper.step(stepsPerRevolution/100); 
}