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How can ROS communicate with my microcontroller?

asked 2011-05-30 16:06:43 -0500

updated 2014-01-28 17:09:46 -0500

Some recent questions have shown an interest in how ROS can be used to run a motor or read a sensor on a custom robot. Many hobby robots have one or more microcontrollers that interface with the robot hardware. These microcontrollers should be able to communicate using a serial connection to a robot mounted laptop running ROS.

The avr_bridge is a sophisticated approach, but it requires a larger AVR processor and C++ code development on the microcontroller which may not be available in some circumstances. Is there a simpler alternative?

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@Bart - Can you provide a bit more explanation on when avr_bridge isn't suitable, perhaps chips you've had an issue with? I've been using it with the Arduino Duemilanove (ATmega328) and have been quite happy with its functionality. Thanks! baalexander ( 2011-05-31 03:00:32 -0500 )edit
I have an ATmega16 that is already 85% full with ISR's, servo control and sensor processing. Some AVR's use a variant of Basic for programming. Some people are loyal to PIC microprocessors. I would like to try avr_bridge on my ATmega128 for a future project. Bart ( 2011-05-31 17:06:41 -0500 )edit

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answered 2011-05-30 16:08:29 -0500

updated 2011-05-30 16:20:01 -0500

A simple approach is to write a ROS node that can read/write text messages exchanged with the microcontroller over a serial port and convert these serial messages to ROS style std_msgs/String messages. A separate ROS node can then be written to convert the simple text messages to specific ROS message formats (cmd_vel, odom, etc) based on whatever message protocol was defined for the exchange with the microcontroller.

Attached below is the source for code that I used for this purpose. There is nothing original in the code, but it may be helpful to someone new to ROS and Unix/Linux serial communication. Posting this type of a listing may be a bit unconventional for this site as short answers are generally preferred. Hopefully no one is offended. I would be interested in hearing if there are other successful approaches to the problem.

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//r2Serial.cpp

// communicate via RS232 serial with a remote uController. 
// communicate with ROS using String type messages.
// subscribe to command messages from ROS
// publish command responses to ROS

// program parameters - ucontroller# (0,1), serial port, baud rate

//Thread main
//  Subscribe to ROS String messages and send as commands to uController
//Thread receive
//  Wait for responses from uController and publish as a ROS messages


#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <stdlib.h>

#define DEFAULT_BAUDRATE 19200
#define DEFAULT_SERIALPORT "/dev/ttyUSB0"

//Global data
FILE *fpSerial = NULL;   //serial port file pointer
ros::Publisher ucResponseMsg;
ros::Subscriber ucCommandMsg;
int ucIndex;          //ucontroller index number


//Initialize serial port, return file ...
(more)
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Interesting, but a lot of my serial stuff is send a message and receive a response back. Instead of separate publish/subscribes have you tried a service? That seems like it would work nicely for this.

Kevin ( 2012-02-22 15:51:55 -0500 )edit
1

answered 2012-02-22 13:04:32 -0500

This seems to be exactly what I need... I think... but may be a little over my head so I will likely have a few questions regarding how to set this up. I'm using an arm attached to a BS2. I have a Roomba platform (that will have the arm attached) being controlled via a laptop running Ubuntu/ROS with web based control via php pages. I would like to use ROS to control the arm as well but I'm unsure of some of the basics. I have the ARM working through the Basic Stamp and I'm able to control the arm via the laptop keyboard... should I keep the BS2 microcontroller and send serial commands using the code above (if so, I'll have other questions)... or, is it better (even feasible...) to bypass the microcontroller and send commands directly to the arm using ROS? I think this is possible, but I'm a novice and need help connecting the dots. Any advice is greatly appreciated!

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Agree, Bart's answer is cool, but is over kill for a beginner. If you pull out the thread stuff, but keep the serial setup, you can make something like the tutorials that talks to a serial port in the while loop.

Kevin ( 2012-02-22 14:31:16 -0500 )edit
0

answered 2012-11-19 23:57:06 -0500

Hi Bart,

My suggestion would be to use the cereal_port pkg on the serial_communication stack, you can install it on Fuerte by apt-get.

sudo apt-get install ros-fuerte-seria-communication

http://ros.org/wiki/cereal_port

Its a ROS C++ wrapper for serial port reading and writing with a bunch of helpful functions such as readLine, readBetween, etc!

Hope this helps,

Gonçalo Cabrita

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answered 2012-02-23 03:57:53 -0500

updated 2012-02-23 04:02:10 -0500

Thanks Kevin. I was thinking this must be simpler than that looks. You mention above using a service. Do you have an example? Does anyone have an example of python code that connects to a serial port (a linked USB in my case) and sends integers to a Microcontroller (BS2 in my case). I'll plug away with the publish/subscribe tutorials but it doesn't have the serial port part. I'm using the BS2 to actuate an arm. Thanks! Kevin

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Please use the comment tags when replying to messages. Also commenting on an accepted question will not get you much help usually. If it's been accepted and closed for months I suggest you ask a new question referencing this one.

tfoote ( 2012-02-23 05:31:38 -0500 )edit

I played around with Bart's code and did a service. It seems to work pretty good. I am re-writing one of my robots to take advantage of it and see how ti works. Good Luck!!!

Kevin ( 2012-02-26 15:00:16 -0500 )edit
0

answered 2012-11-19 18:42:25 -0500

updated 2012-11-19 18:44:34 -0500

this code is really very helpful for me. thnaks for this code and updates http://www.altaworx.com (sip telephone service)

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Asked: 2011-05-30 16:06:43 -0500

Seen: 3,356 times

Last updated: Nov 19 '12