Sony Arouje Blog

a programmer's log

Connecting XBee to Raspberry pi

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Last one week I was doing some research in RF communication and controlling devices using RF. So what am I going to control here, I wanted to control the water pump running in my hydroponic reservoir without running wires from my raspberry pi. This way I can extend my hydroponic system to more balconies without buying extra RPi, a single RPi will send a switch on/off command and the RF client will switch on/off the motor via a relay. Also I don’t need to setup a wifi network in my controller RPi’s.

My research for RF communication platform leads to Zigbee protocol and XBee component. XBee is a very popular Zigbee complaint product from Digi. For my testing I got two XBee Pro S2 and two XBee explorer. The explorer I bought uses USB to A/B cable, if you are buying it make sure buy A/B cable as well. You will get micro usb explorer as well.

To configure the XBee’s I use the X-CTU software from Digi, you can download it free from Digi’s website. I use the Legacy X-CTU for configuring my modules and Next Generation X-CTU for issuing commands. Configuration is pretty simple and so many sites will walk you through it. I configure my XBee’s as shown below. One XBee act as Coordinator and enabled API mode and another XBee act as router and enabled Router AT.

XBee Coordinator

  • Modem: XBP24-ZB
  • PAN: <set a pan id, say 123>
  • Destination Address Low: FFFF

XBee Router

  • Modem: XBP24-ZB
  • Function Set: ZIGBEE ROUTER AT
  • PAN: <set a pan id, say 123>
  • Destination Address Low: 0000

I left all other settings as default.

Connecting to Raspberry pi

For testing I connected the XBee coordinator to my computer and XBee Router to my RPi. In RPi I created a simple node app to send some text message to coordinator. Below diagram will show you, how I connected Router XBee to my RPi. Here we use serial communication between RPi and XBee. RPi has only one set of serial communication pin and by default it’s configured for console I/O, there are so many tutorial out there to free it up and I use one from them.


image developed using Fritzing

I connected the XBee directly using jumper wires, the above diagram is just for illustration for that I use the breadboard.

Connect RPi 3.3 volt to XBee 3.3 volt pin, Ground to XBee ground, Rx to Xbee Tx (Data Out), Tx to XBee Rx (Data In).

Sending some data from Router Xbee to Coordinator

Now I wanted to send some data from Router XBee connected to my RPi  to the coordinator connected to my Computer.

I created a small app using node js, below is the code. To run the code we have to install two node modules.

  • xbee-api: npm install xbee-api
  • serialport: npm install serialport
var util = require('util');
var SerialPort = require('serialport').SerialPort;
var xbee_api = require('xbee-api');

var C = xbee_api.constants;

var xbeeAPI = new xbee_api.XBeeAPI({
    api_mode: 1

var serialport = new SerialPort("/dev/ttyAMA0", {
    baudrate: 9600,
    parser: xbeeAPI.rawParser()

serialport.on("open", function () {
    var frame_obj = {
        type: 0x10, 
        id: 0x01, 
        destination64: "0013A200407A25A7",
        broadcastRadius: 0x00,
        options: 0x00, 
        data: "Hello world" 
    console.log('Sent to serial port.');

serialport.on('data', function (data) {
    console.log('data received: ' + data);

// All frames parsed by the XBee will be emitted here
xbeeAPI.on("frame_object", function (frame) {
    console.log(">>", frame);


When I run the above node app, I can see the data receiving in my Coordinator’s X-CTU app. I could also send a Remote AT (0x17) command to the router to one of the Digital pin and could turn On/Off a LED.

Seems like the communication is working fine. Let’s see what I can come up next.



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Written by Sony Arouje

December 20, 2014 at 6:07 pm

Posted in Raspberry Pi

Tagged with , ,

Working of my very basic and crude Aeroponic System

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Here I will just show you a video of my Aeroponic system. As you can see its very basic, I didn’t want to spend much money to test whether my system works, so I used cost effective materials.

In one of my previous post I explained about how I used Rasberry pi to control the motor. If you haven’t read it, please check that out too.


Low Pressure Aeroponic System


What Next?

  • From this initial test run, I could see my system is a success. Now I will add more pillars and a high capacity tank.
  • Automate day to day activities. For e.g. I have to add nutrients to the reservoir once in two day. Using a Peristaltic pump and a motor driver I can automate the process with a click of a button from my mobile app. 

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Written by Sony Arouje

December 11, 2014 at 2:22 pm

Posted in Raspberry Pi

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Distributed Raspberry pi based Hydroponic Controller

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Last couple of weeks I was building a Hydroponic system controlled by Raspberry pi. As of yesterday night my system was based on a single Raspberry pi that control one or more water pumps. It was one of my design goal to add more Pi’s based controllers to the network with zero configuration.

Why more Controllers?

As I am living in an apartment and the hydroponic system is going to be installed in the balconies. Connecting the motors installed in different balconies to a single Raspberry controller will make things ugly, I don’t want wires hanging here and there. So one option is, add another Raspberry pi controller. It’s easily doable, just install the controller software I created and plug the water pump.

As I explained in my last post, this system is controlled via mobile devices. So when ever I add a controller to my hydroponic network I have to create an entry in each of the device in which my mobile app installed. Also I have to assign a static ip to each Raspberry controller or keep track of the host name. When I start thinking about it, I see a system with some complications. Yesterday night I modified my controller application, this is what I come up with.

Unifying server and Controllers with self advertisement

I created a Unifying server in node js. The controller system running in different Raspberry pi’s advertise about it when ever it joins to my wifi network. This Unifying server will get notification whenever a new controller joins. I use Node Discovery module for service discovery and publishing. In this scenario I don’t have to worry about any configuration of the controllers. Just install my controller software in each raspberry pi and plug it into my hydroponic system.

My mobile app connects to this unifying server instead of individual controller system. All the commands to the controllers will be routed via this unifying server to respective controller. Below is the routing function I come up with.

app.use('/', router);
router.use(function (req, res, next) { = req.headers.hostid;
    options.path = req.originalUrl;
    options.method = req.method;

    var request = http.request(options, function (response) {
            response.on('data', function (data) {
                res.setHeader('content-type', 'application/json');
        if (req.method === 'POST') {
            request.setHeader('content-type', 'application/json');


This unifying server is a very light weight system and can run in a Raspberry pi or in my computer. On of my design goal is that Controller should be self sufficient and should run in any circumstances even if there is no connection to unifying server.

The Unifying server and the Controller system is based on Node js. It’s a beautiful platform and I learned a lot about node js while building this system. Also become a huge fan of Javascript.


Next post I will go through the mobile app I created.


Happy coding…

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Written by Sony Arouje

November 22, 2014 at 5:37 pm

Posted in Raspberry Pi

Tagged with ,

Hydroponics system controlled by Raspberry Pi an overview

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Last couple of weeks I was spending my free time to understand and building a Hydroponic system to grow vegetables in my Apartment’s Balcony. I just don’t want to build a normal system that controlled by a timer, instead I want to build a system that I should be able to monitor even I am not at home, change watering schedule using my mobile device.

Before we jump into details, let me give you a brief about Hydroponic.

What is Hydroponics?

In simple terms, hydroponic is a system where you can grow vegetables without soil, mix the required nutrients in water and feed directly to plants. Advantage of this system is, we are feeding plants what they want, instead plant hunting for the nutrients from soil. Also less consumption of water as we reuse the water.

If you search in google you will get more details of Hydroponics. I am working on a subset of Hydroponic called Aeroponics, where plants grow vertically. I made the vertical growing tower based on the method described by Gunnar Shaffer.

Any Hydroponic system needs water circulation using a water pump, I used a submersible pump bought from Ebay for 225.00 INR. This pump should pump water in a periodical manner, say water for 15 mins then sleep for 60 mins and the cycle continues. We can use a timer to do that, it will cost from 1500 – 2500 INR. I decided to use one of the Raspberry pi lying in my table.

Why Raspberry pi?

As a programmer, this small brilliant device give me the flexibility of controlling the system with the programming language of my choice. For this system I used Node js platform to build the controller system. I spent a night to build the basic system that can turn on/off any device in a specific interval and some REST api’s through which mobile device can interact. Later I spent several nights to polish and enhancing my system.

For my testing I used a breadboard to turn off/on one LED. After I successfully controlled the LED, it’s the time to control the Electrical motor. I bought a 12v single channel Relay from ebay for 99.00 INR. It can control one electrical device, in my case the submersible water pump. This post will give you an idea about how to connect the Relay to your Raspberry pi.

Mobile Application

After I completed the system running in Raspberry pi, I decided to write the application for the mobile device. Through which I can interact with the system. As of now the application can

  • Turn off the pump, in case of maintenance.
  • Schedule watering interval.
  • Turn on motor to water immediately.

The mobile application is written using Cordova platform, so that app can run on my Windows or Android devices.

What Next?

  • The basic infrastructure is done, next important step is start growing veggies. It got delayed because I am waiting for two meters to measure the water content. The pH and TDS meter.
  • Suggestion system for nutrient quantity based on the previous data.
  • Distributed cluster of Pi based Aeroponics blocks controlled by a server.
  • Connect Water level monitor to Rasp pi and notify if water level of the tank goes down.

Update: see my hydroponic in action.

Thanks to

  • My wife, for her support and encouragement, for all the crazy stuffs that I am experimenting with.
  • My father who guides and clarifies all my question related to Electrical devices and suggestions to improve the system for better performance.
  • Gardenguru for providing me with key information like measuring and controlling ph and EC level. I also bought the necessary items from them like Net Cups, Hydrotons, Nutrients, etc. They have a shop near to my home, I go there and spent time talking with them. They are very enthusiastic and provide with any info about Hydroponic to a newbie like me.


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Written by Sony Arouje

November 10, 2014 at 1:21 pm

Posted in Raspberry Pi

Tagged with ,

Node js error handling using modules inherited from EventEmitter

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In node js most of the operations are asynchronous and normal try-catch will not work. In case of any error and we didn’t handle it properly, our node process will crash. In this post I will explain how to handle errors properly using EventEmitter.

In this e.g. we are going to read some data from a SQLite db, I use dblite as my node module to deal with SQLite db. For this e.g. I created a UserRepository module and inherited from EventEmitter


var dblite = require('dblite');
var util = require('util');
var EventEmitter = require('events').EventEmitter;

var UserRepository = function () {
    var self = this;

    self.getUser = function (userid, callback) {
        db.query('select * from USER where USER_ID=:id', [], { id: userId },
        function (err, rows) {
            if (err)


    var publishErr = function (err) {
        self.emit('error', err);

util.inherits(UserRepository, EventEmitter);
module.exports = UserRepository;


Using util.inherits, we inherits the UserRepository module from EventEmitter. Later we export that module to use in other node modules. The publishErr() function will emit an ‘error’ event in case of any error and calling module can subscribe to that event and handle the error.

Let’s use the above module in another node module. Say an express rest api.


var express = require('express');
var bodyParser = require('body-parser')

var UserRepository = require('./UserRepository');
var userRepo = new UserRepository();

var app = express();

userRepo.on('error', function (err) {

app.get('/users/;id', function (req, res) {
    userRepo.getUser(, function (record) { 



Let’s go through the lines in bold.

Here we are creating the instance of UserRepository module.

var UserRepository = require('./UserRepository');
var userRepo = new UserRepository();

The calling module should subscribe for the error event, that’s what we are doing here. I am just writing the error to the console. You can do whatever you want with that err object.

userRepo.on('error', function (err) {


This way we can ensure that our errors are handled properly in an elegant way.

Node js has an uncaughtException event and use it as a last resort.

process.on('uncaughtException', function (err) {

Written by Sony Arouje

November 7, 2014 at 5:47 pm

Posted in .NET

VS2013 Multi-Device Hybrid Apps and Network Error in Windows8

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Last couple of days I was working on Node js REST service running in one of my Raspberry Pi. The idea is to do certain stuffs remotely via mobile devices. Later I will write a post explaining the project in detail. I completed Phase 1 of the application running in Raspberry pi. So next task was creating a mobile app, I decided to use Cordova with VS 2013 Multi Device Hybrid app template.

Yesterday night I started working on the Hybrid app in VS 2013 for Windows 8. First thing I wanted to test was the connectivity to the REST service running in Raspberry pi. I used Angular js $http to connect to the REST service. To my surprise what ever I do, the app is throwing error while doing http post with status 0. The same code works successfully if I run as a web app.

I spend a hell lot of time to figure out the issue but no success. Then I decided to use fiddler to test the traffic, when fiddler is running the app could able to communicate with the REST service. I got a hint, when we run Fiddler in Win8, it adds apps to AppContainer Loopback exemption. If I exempt my windows 8 app then http request starts failing. This stage I realized that, the error is because of some app configuration issue. Also in VS Java Script console I could see the error as shown below.

XMLHttpRequest: Network Error 0x2efd, Could not complete the operation due to error 00002efd.

All my google search return nothing. After a long hours of desperate research I came to know that to access private network I need to add Private Network capability to windows 8 app. But I didn’t know how to add it for Hybrid app as there is no Capabilities section in the config.xml. Some more search leads me to the Faq page of Multi device hybrid app template. As per the FAQ page we can override the default AppManifest.xml as shown below.

1. Create a Package.appxmanifest file under res/cert/windows8. Create a windows8 solution folder if not exist.

2. Open the project folder and go to bld/windows-AnyCpu/Debug and open AppxManifest.xml in notepad, copy the content and paste it in the above Package.appxmanifest file.

3. Double click on Package.appxmanifest file then goto Capabilities tab and choose ‘Private Networks (Client & Server)’.

4. Save it and run the app again, this time it worked I could connect to my Node js REST api.


Hope this will help some one to solve the XMLHttpRequest issue.


Happy Coding…

Written by Sony Arouje

October 29, 2014 at 3:50 pm

Chat application using SignalR 2.1

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Around two years ago I published a post about SignalR. Recently some readers requested an updated post using SignalR 2.1, here is the updated one.

For this post I created a very simple chat application that hosted in IIS, developed in .NET 4.5. Below is the project structure.

  • SignalrTracer.ChatServer: An empty ASP.NET Web Application which host the SignalR hub.
  • SignalrTracer.Publisher: A class library project that has SignalR hubs. I created this project just to isolate SignalR hubs from the ChatServer.
  • SignalrTracer.ChatClient: Another empty ASP.Net Web Application act as the client.



As I mentioned above, this project contains the SignalR hubs. We can add SignalR framework using Nuget package manager.

Open Package Manager Console from Tools->Nuget Pacakger Manager and choose SignalrTracer.Published as the Default Project in the console window, then enter

PM> Install-Package Microsoft.AspNet.SignalR.Core

The command will add the SignalR and dependent frameworks. It’s time to create our chat hub.


using Microsoft.AspNet.SignalR;
namespace SignalrTracer.Publisher
    public class ChatHub:Hub
        public void Subscribe(string chatId)
            Groups.Add(Context.ConnectionId, chatId);

        public void Publish(string toChatId, string message)


SignalR 2.1 relies on OWIN to host it. For that we need to create a Startup class as shown below.

using Microsoft.Owin;
using Owin;
using Microsoft.AspNet.SignalR;
[assembly: OwinStartup(typeof(SignalrTracer.Publisher.Startup))]
namespace SignalrTracer.Publisher
    public class Startup
        public void Configuration(IAppBuilder app)
            // For more information on how to configure your application, visit
            var hubConfig = new HubConfiguration();
            hubConfig.EnableDetailedErrors = true;
            hubConfig.EnableJSONP = true;
            app.MapSignalR("/chatserver", hubConfig);

            app.Run(async context =>
                await context.Response.WriteAsync("Chat server started");

That’s it we created our SignalR hub. Let’s host it in our ChatServer.


This project is a OWIN host, to do that we need to refer another Nuget package called Microsoft.Owin.Host.SystemWeb.

Open the Nuget Package Manager Console and set Default project as SignalrTracer.ChatServer, then enter

PM> Install-Package Microsoft.Owin.Host.SystemWeb

Once all the package installed, just refer SignalrTracer.Publisher project and run the project. If every thing is fine then you can see an Internet Explorer with a string Chat server started. This means SignalR hub is up and running and any clients can connect now.



I used Javascript to connect to SignalR server. Open Nuget Package Manager Console and enter

PM> Install-Package Microsoft.AspNet.SignalR.JS

It will install JQuery and JQuery extension of SignalR client. I created an index.html and added the code below.

<!DOCTYPE html>
<html xmlns="">
    <script src="Scripts/jquery-1.6.4.min.js"></script>
    <script src="Scripts/jquery.signalR-2.1.2.min.js"></script>
    <script type="text/javascript">
    $(function () {
        var connection = $.hubConnection('http://localhost:35144/chatserver');
        var proxy = connection.createHubProxy('ChatHub');
                .done(function () {
                    $('#messages').append('<li>Connected to chat</li>');
                .fail(function () { alert("Could not Connect!"); });

        proxy.on('flush', function (msg) {
            $('#messages').append('<li>' + msg + '</li>');

        $("#send").click(function () {
            proxy.invoke('Publish', $("#sendTochatId").val(), $("#message").val());

        $("#connect").click(function () {
            proxy.invoke('subscribe', $("#chatId").val());
            $('#messages').append('<li>subscribed to chat</li>');


    <label>Chat id</label> <input type="text" id="chatId" /><input type="button" id="connect" value="Connect" /><br />
    <label>Send To</label> <input type="text" id="sendTochatId" /><br />
    <label>Message</label> <input type="text" id="message" />
    <input type="button" id="send" value="Send"/>
        <ul id="messages"></ul>


You might need to change the url of hubConnection marked in bold.

Once the connection established messages section will get appended with ‘Connected to chat’ message.

Enter a unique Id in Chat Id text and click Connect, open multiple window and connect with different chat id’s.


As you can see it’s a very basic and simple chat system based on SignalR.

Source Code

Happy coding…

Written by Sony Arouje

September 18, 2014 at 12:49 am

Posted in .NET

Tagged with ,


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