Monday, September 8, 2014

Getting data from camera in Robot Operating System

I have used webcams in OpenCV before.

However, I came across a situation where I had to stream the webcam data to a ROS (Robot Operating System) topic.

There are bunch of ROS packages on ros.org website. However, when I did a

it gave me errors saying there was no such package found.

All I want to do is grab the data from a webcam and post it to a topic (so that other ROS nodes can read from that topic). I knew it had to be simple

So, I came across this deb package in Ubuntu

Once, I did the above installation all I had to do was


Then, it started publishing data onto /image_raw topic.

Then I could do a


To read the data from the camera published on the topic.

To get a list of topics published to, do a

If you ran the above command, you could infer that the published image stream is of type /sensor_msgs/Image

Wednesday, February 5, 2014

fun with my Raspberry Pi

I ordered a Raspberry Pi recently. I've heard so much about this device in the recent past, I decide to try it out. I was reminded of few microprocessor(fun class) and electrical engineering(not so fun time) classes that I took in my undergrad. I wrote a simple program that could turn a Stepper Motor using a motor controller connected to a Raspberry Pi.

Raspberry was only 35$. If you are planning to buy it, it might cost you a little more than that if you don't have the necessary stuff required.

This is what i used (physical stuff) to run a simple Python Program to turn a stepper motor using Raspberry Pi:

  1. Raspberry Pi (Duh! ) model B (model B has 2 USB slots, HDMI, ethernet, you can fit keyboard, mouse, wifi dongle, etc). I guess model A has fewer of these slots and no HDMI.
  2. 4 GB + memory card (the Raspbian OS is just over 2 GB, so won't fit on a 2GB card). I guess any one will do. You can use the ones that go with your camera.
  3. HDMI cable to connect to a TV or monitor.
  4. Power Cable (get an external power adapter for Raspberry Pi).
  5. Screw driver set, if you don't have one (it comes in handy if you are messing with electronics). I got this one.
  6. Jumper cables.
  7. Battery holder for powering the stepper motor.
  8. WiFi dongle. Yes, Raspberry Pi (model B) doesn't come with builtin WiFi. So, I got this one. I didn't have any problems with drivers, etc.
  9. Stepper motor. This one comes with a tire. It will come in handy if are into Robotics.
If you add all these, you might end up spending around $70-$100.

I formatted the SD card with Raspbian OS (its a variant of Debian). Its customized to run on ARM architecture.


I followed the instructions posted on this video on YouTube.

The code that I have below was obtained from above video:


Once you have the program, you need to open the Terminal in Raspberry Pi and give the command as a root to run the program. For example,
Here is a video of the working system:

Thursday, January 30, 2014

setting up Ad-hoc network in Ubuntu 12.04 or Debian

I had a hard time looking for setting up an Ad-hoc network. This post explains to setup an ad-hoc network in one of the most easiest ways.

The basic idea behind setting this up is, set up an ad-hoc network on your both (or more) computers individually and let them talk (or ping) to each other.

One needs to understand that ad-hoc network is different from a WiFi hotspot. Also you need to be patient while one computer pings another.

You will have to do the following in both(or more, replace the ip addresses) of the computers
In first computer (copy paste the following text), you give the network name and other important details for the interface that you are configuring ad-hoc for.
Similarly, in second computer
Now back in ther terminal do the following:

ifup command is a very useful command.

That's all. You adhoc network is now setup. Now to be sure if everything is okay, you could do the following:

Now, all is left is to ping first computer from second computer (or vice-versa) to make sure that everything works well.
Now have some patience wait for some time till they ping each other
Once the network is established (at least once), the further attempts to reconnect (in case of a disconnect) will be much faster.

Reference: https://wiki.debian.org/WiFi/AdHoc