Linux Tips and Tricks

This post contains some tips and tricks that helps resolve problems that i've encountered when working with Linux, mostly Ubuntu.

Ubuntu: Install 32 bits libraries on 64 bits system

Some of my applications are 32 bits only which sometime depend on several 32 bits libraries. By default, ubuntu installed only the 64 bits version of these libraries. To installed the 32 bit ones, we need enable the i386 architecture using dpkg, these following commands should be executed as root:

Simple (naive) document clustering using tf-idf and k-mean

When i developed this blog (using my own client-server platform such as web server, back-end, front-end, etc., built from ash/scratch :) ), i simply designed it as a simple "note book" where i put my ideas or some stuffs that i have done. So, initially, there are no category no advance feature like post suggestion based on current post, etc. It is just a bunch of posts sorting by date. The thing is, i usually work on many different domains (robotic, IoT, backend, frontend platform design, etc.), so my posts are mixed up between different categories. It is fine for me, but is a real inconvenience for readers who want to follow up their interesting category on the blog. Of course, i could redesign the blog and add the missing features by messing around with the relational database design (i'm using SQLite btw), manually classifying the posts in the back-end, etc. But, i'm a kind of lazy people, so i've been thinking of a more automatic solution. How about an automatic document clustering feature based on a data mining approach ? Here we go!

Adding noise to odometry data published by the Gazebo simulator

I've had funny time playing around with the Gazebo simulator for autonomous robot exploration. One thing I've encountered is that the odometry data provided by Gazebo is so perfect that, sometime, makes the simulation less realistic. I used a Turtlebot model as robot model in my simulations. Googling around, i didn't find any solution of adding noise to the odometry data of this robot (using the URDF file). I then decided to develop a dedicated ROS node allowing me to add some random noise to the Gazebo's odometry data.

The robot motion model

First thing fist, we need to understand the robot motion model. There are many motion models, but in the scope of this article, we focus only on the odometry motion model. Often, odometry is obtained by integrating sensor reading from wheel encoders, it measures the relative motion of the robot between time \(t\) and \(t-1\) or \((t-1,t]\). In 2D environment, a robot pose is represented by a point \((x,y)\) and an orientation (rotation angle) \(\theta\), so the robot pose at the time \(t-1\) and \(t\) are denoted by:
$$p_{t-1}=(x_{t-1},y_{t-1},\theta_{t-1})$$
$$p_{t}=(x_t,y_t,\theta_t)$$

Setting up a software stack for autonomous mono robot exploration and mapping using ROS

Prerequisites

This setup is performed and documented on an Ubuntu system with the following software stack:

  • Ubuntu 16.04 LTS (may work on other distribution though)
  • ROS kinetic: if you don't have ROS pre-installed, please refer to this tutorial http://wiki.ros.org/kinetic/Installation/Ubuntu. I suggest to use the full desktop installation configuration, this will take a while (> 2 GB)
  • Gazebo for simulation (it is installed by default if you choose the full desktop installation when installing ROS)
  • GIT (sudo apt-get install git)
  • Catkin for package building (installed by default when installing ROS)

To follow this post, some basic knowledge on ROS is needed:

AntOS v 0.2.3-alpha release: AntOSDK - a development kit for AntOS application

A new release of AntOS, it is now in the beta state, but i'll keep the alpha branch on the release for a few further releases.

Change logs

  • Fix bugs and improve stability
  • DotEditor app is renamed to GraphEditor and use mermaid to generate graphs instead of dot
  • AntOS in now under GPLv3 licence, if you want to use it for comercial purpose, please contact me
  • Blogger is no longer default application, it is moved to MarketPlace
  • Add svg support to Preview
  • MarketPlace now can detect if an application update is available
  • Add AntoSDK, a development kit that allows to develop, build, and package your own application right in the browser, it is available on MarketPlace
  • New UI elements: afx-slider, tooltip

AntOS 0.2.0a "Localization" release

AntOS 0.2.0-alpha is out now. The big change in this release is the support of localization. The UI now support multi-languages rendering based on the current system locale setting.

Github: https://github.com/lxsang/antos
Demo: https://os.lxsang.me

Change logs

  • The API now automatically translate text base on the current system locale setting
  • Current locales supported:
    • English: en_GB
    • French: fr_FR
    • Vietnamese: vi_VN
    • More to come...
  • Update all packages to support the new localization mechanism
  • Some minor changes:
    • Font-awesome is used as default icon font for the entire system
    • Add Setting package for system configuration
    • Wallpaper, language, VFS and startup applications/services now can be configured via Setting
    • Bug fix on some packages: File, Market Place
    • Stability improvement

AntOS web desktop 0.1.11-alpha release

I've started the development of the AntOS web desktop long time ago, but this post is the first official pre-release of the project. The idea on a web-based desktop came when i worked on embed Linux and remote server. These system are often headless, so accessing the resource on these systems is not always obvious. The aim of this project is to develop a client core API that provides a desktop like experience to remotely access resource on the server using web technologies. AntOS is based on jQuery (for the API development) and Riot JS (for the UI), it is first designed to be used along with my antd HTTP(S) server and Lua based server side app, but can be adapted to be used with any server side languages (PHP, etc) and server, by implementing all the system calls API . Basically, application design for the web desktop relies on these system calls to communicating with the server. The API defines the core UI, system calls (to server), Virtual File system, virtual database and the necessary libraries for easing the development of applications. Applications can be developped with coffee/javascript/css without the need of a server side script.


(click image for the full size version)

Interfacing Raspberry Pi and LPC1114FN28 via SPI

In one of my previous posts, i mentioned about building a toy car project using Raspberry Pi as the brain and the LPC1114FN28 for low level control. This post describes in detail of this hobby project.

Basically, in this project, the Raspberry Pi (running a minimal version of Debian, not Rasbian) acts as a master that :

  1. performs some high level calculation (software algorithm) base on the data it collects from the LPC chip (slave)
  2. Issues a control command to the slave chip (LPC) for low level control
  3. Reading image from Raspberry Camera for some vision stuffs
  4. Takes care of network communication for remote control
  5. Implements easily a lot of funny stuffs...

One question: why do not use the Pi to communicate directly with sensor or actuator ?. Although the Pi is a pretty performance system, it lacks some low level feature that we will need in this project, such as ADC for reading analog sensors, precise PWM hardware controller for motor control, etc. Therefore, i decided to used it along with the LPC chip that is more suitable for these low level stuffs.

Programming LPC1114FN28 with standard C using Newlib

Some of my old posts show how to program the ARM Cortex M0 LPC chip in a bare metal manner, although this approach provides a simple setup that requires no additional libraries, it is only for the studying purpose. It is not a good options for production since your code will be highly platform dependent and you need to handle so many low level stuffs (e.g. registers configuration). The Newlib offers a more productive way by providing a standard C interface to abstract the development on such embedded system. In using Newlib, the code is a lot simpler and more portable.

25/02/2018 LPC1114FN28, ARM, GPIO, interrupt

Arm-cortex m0 programming with LPC1114FN28 , a guild to GPIOs

This is a migrated version of my Wordpress post, written on : 14 Mars 2015

Input/Output

The LPC1114FN28 has two pin ports (0 and 1) that make totally 22 pins (12 for port 0 and 10 for port 1, as shown in the image below). All of these pins could be used as GPIOs. By default, they are all input and pull up-enable (that is each pin is connected to an internal pull-up resistor) except for PIO0_5 (dp5) and PIO04 (dp27) which are "open-drain" (a transistor connects to low and nothing else). Their functionalities can be configured easily by software.

The figure below shows the pin out of the chip, note that each PIOn_m refers to the pin m on the port n.

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