Miłosz Orzeł

.net, js, html, arduino, java... no rants or clickbaits.

[OoB] Sonar with Arduino, C#, JavaScript and HTML5 (Part 2)

Part 1 described the general idea behind Sonar project, hardware components used and Arduino sketch... This second post in "Out of Boredom" series is about C# and JavaScript programs that make it possible to display ultrasonic range sensor data in web browsers. The role of .NET application is to receive messages from Arduino over serial port and broadcast it to clients using SignalR library. JS/HTML5 clients use jquery.signalR lib to obtain information about servo position with distance to obstacles and use this data to render sonar image on canvas:

Sonar client image... Click to enlarge...

These links are in previous post, but just to remind you:


1. SonarServer 

SonarServer is a .NET 4.5 console app created in Visual Studio Express 2013 for Windows Desktop. It uses Microsoft.AspNet.SignalR.SelfHost and Microsoft.Owin.Cors NuGet packages to create self-hosted SignalR server. ASP.NET SignalR is a library designed to make it easy to create applications that are able to push data to clients running in web browsers. This is in contrast to normal web pages/apps behavior where the client (browser) asks server for action by issuing a request (such as GET or POST). SignalR allows clients to listen for messages send by a server... If possible SignalR will use WebSockets to enable efficient bi-directorial connection. If that option is not available due to either browser or server limitations, it will automatically switch to other push techniques like long polling or Server-Sent Events. When I tested the code on my laptop with Windows 7 Home Premium SP1, long polling was used on IE 11 and SSE in Chrome 37. Server was sending about 20 messages per second and clients didn't have any problems with handling that load (communication was on localhost). Self-hosting means that SignalR server doesn't have to be run on a web server such as IIS - it can exist in plain old console project! If you are completely new to SignalR check this tutorial... 

This is SonarServer project structure:

SonarServer solution...

SonarData.cs file contains such struct:

namespace SonarServer
    public struct SonarData
        public byte Angle { get; set; }
        public byte Distance { get; set; }

Server will send a list of such objects to clients.

SonarHub.cs contains a class derived form Hub. It doesn't declare any methods but is nonetheless useful. Library will use it to generate JavaScript proxy objects...

using Microsoft.AspNet.SignalR;

namespace SonarServer
    public class SonarHub : Hub


Startup.cs file looks like this:

using Microsoft.Owin.Cors;
using Owin;

namespace SonarServer
    class Startup
        public void Configuration(IAppBuilder app)

It configures the SignalR server, letting it support cross-domain connection thanks to UseCors call.

Below are the most important bits of Program.cs file. This code:

using (SerialPort sp = new SerialPort())
     sp.PortName = "COM3";
     sp.ReceivedBytesThreshold = 3;
     sp.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);


     Console.WriteLine("Serial port opened!");

     using (WebApp.Start<Startup>("http://localhost:8080/"))
         Console.WriteLine("Server running!");

is responsible for opening a connection with Arduino over serial port named "COM3" and starting SignalR server on localhost:8080ReceivedBytesThreshold property allows us to control the amount of bytes received from Arduino before DataReceivedHandler is called. You can increase this value if you want bigger packages of data to be broadcasted by server and rendered by clients. This is the part of DataReceivedHandler method that loads serial port data into a byte array:

int count = sp.BytesToRead;
[] data = new byte[count];
sp.Read(data, 0, count);

Such array of bytes is latter on added to custom buffer and processed to create a list of SonarData objects sent to SignalR clients. Part 1 mentioned that Arduino sends data to PC in bytes (array) packages containing three elements: [255, angle, distance]. The purpose of special 255 value is to separate angle-distance pairs of values which are used to create sonar image. We can't just send [angle, distance] stream from Arduino to PC, because the Server could easily loose track of which value is angle and which is distance. This might happen due to delays, buffering etc. Sure it's not a bulletproof protocol but it work well when I tested it. Lot's not get crazy with that - it's a hobby project, remember? :) Check ProcessSonarData method in repository if you want to see how an array of bytes is turned into SonarData list (with buffering taken into account)... 

The last missing piece of SonarServer puzzle is SendSonarDataToClients method:

private static void SendSonarDataToClients(List<SonarData> sonarDataForClients)
    var hub = GlobalHost.ConnectionManager.GetHubContext<SonarHub>();

    Console.WriteLine("Sonar data items sent to clients. Samples count=" + sonarDataForClients.Count);

This is the thing that actually broadcasts data to clients running in web browsers. You may be wondering why SonarHub instance is not created directly with new operator and instead GetHubContext method is used. This is because SignalR is responsible for its hubs life cycle. Such code:

SonarHub sonarHub = new SonarHub();

would result in the exception: System.InvalidOperationException: Using a Hub instance not created by the HubPipeline is unsupported." .


2. SonarClient

SonarClient is the subproject responsible for drawing sonar image. It's not a Visual Studio solution - just a few files:

SonarClient files...

I've tested SonarClient code in IE 11 and Chrome 37 and it worked really well. The assumption is that you run modern browser too. I didn't bother with any feature detection, it's enough for me that I have to write for IE9 at work - well, at least it's not IE 6, huh? ;) But if you want to do such thing I can recommend Modernizr library...

This is content of index.html file (with some boring parts removed for brevity):

<!DOCTYPE html>
    <title>Sonar - sample code from morzel.net blog post</title>
        /* more */
        <canvas id="sonarImage" width="410" height="210"></canvas>

              <!-- more -->            

    <a href="http://morzel.net" target="_blank">morzel.net</a>

    <script src="lib/jquery-1.6.4.js"></script>
    <script src="lib/jquery.signalR-2.1.1.js"></script>
    <script src="http://localhost:8080/signalr/hubs"></script>
    <script src="sonarStats.js"></script>
    <script src="sonarImage.js"></script>
    <script src="sonarConnection.js"></script>

        $(function () {          

Most important bit of this HTML5 markup is the canvas element used to create sonar image. The page imports jquery and jquery.signalR libraries that make it possible to communicate with the Server. That line is particularly interesting:

 <script src="http://localhost:8080/signalr/hubs"></script>

SingalR automatically creates JavaScript proxy objects for server-client messaging, that line lets us load them into page. Last three script references are for JS modules responsible for: displaying info about data received from SonarServer, rendering sonar image and communication with server, respectively. Later there's a short script which initializes the modules after pages DOM is ready.

I will skip the description of sonarStats.js file (nothing fancy there - just filling some table cells). But sonarConnection.js should be interesting for you. This is the whole content:

var sonarConnection = (function () {
    'use strict';

    var sonarHub, startTime, numberOfMessages, numberOfSamples;

    var processSonarData = function (sonarData) {
        $.each(sonarData, function (index, item) {
            sonarImage.draw(item.Angle, item.Distance);
            sonarStats.fillTable(item.Angle, item.Distance, startTime, numberOfMessages, numberOfSamples);

    return {
        init: function (url) {
            $.connection.hub.url = url;

            sonarHub = $.connection.sonarHub;

            if (sonarHub) {
                sonarHub.client.sonarData = processSonarData;
                startTime = new Date();
                numberOfMessages = 0;
                numberOfSamples = 0;

            } else {
                alert('Sonar hub not found! Are you sure the server is working and URL is set correctly?');

The init method sets SignalR hub URL along with sonarData handler and starts a connection with the .NET app. There is also some very basic hub availability check (jquery.signalR library has extensive support for connection related events but lets keep things simple here). processSonarData is invoked in response to Server calling hub.Clients.All.sonarData(sonarDataForClients). The processSonarData function receives an array of objects containing information about servo angle and distance to obstacles. SignalR takes care of proper serialization/deserialization of data - you don't have to play with JSON yourself. $.each function (part of jQuery) is used to invoke sonarImage.draw and sonarStats.fillTable methods for every item in sonarData array...

And here comes the module that changes pairs of angle-distance values into o nice sonar image (whole code of sonarImage.js):

var sonarImage = (function () {
    'use strict';

    var maxDistance = 100;
    var canvas, context;

    var fadeSonarLines = function () {
        var imageData = context.getImageData(0, 0, canvas.width, canvas.height),
            pixels = imageData.data,
            fadeStep = 1,

        for (var i = 0; i < pixels.length; i += 4) {
            green = pixels[i + 1];

            fadedGreen = green - fadeStep;
            pixels[i + 1] = fadedGreen;

        context.putImageData(imageData, 0, 0);

    return {
        init: function (canvasId) {
            canvas = document.getElementById(canvasId);
            context = canvas.getContext('2d');

            context.lineWidth = 2;
            context.strokeStyle = '#00FF00';
            context.fillStyle = "#000000";

            context.fillRect(0, 0, canvas.width, canvas.height);

            context.translate(canvas.width / 2, 0);
            context.scale(2, 2);

        draw: function (angle, distance) {

            context.rotate((90 - angle) * Math.PI / 180);
            context.moveTo(0, 0);
            context.lineTo(0, distance || maxDistance); // Treat 0 as above range



Again we have an init method. It obtains 2d drawing context from canvas and uses it to set line width and color (green). It also sets inner color (black) and fills the whole canvas with it. context.translate call is used to move origin of coordinate system to the middle of canvas (horizontally). By default it sits in upper left corner. context.scale is used to make image two times bigger than it would be drawn in default settings. Read this post if you want to know more about canvas coordinates.

The draw method is invoked for each data sample (angle-distance pair) produced by Arduino and broadcasted with SonarServer. The distance to obstacles measured by HC-SR04 sensor is represented as a line. The bigger the distance the longer the line. This happens thanks to beginPath, moveTo, lineTo, and stroke calls. context.rotate method is responsible for showing the angle in which the sensor was pointing while measuring distance (angle of servo arm). As the servo moves around we want to change the direction in which distance line is drawn. Notice that code responsible for drawing the line is surrounded by context.save and context.restore calls. These two ensure that rotation transformation doesn't accumulate between draw method calls...

fadeSonarLines function is responsible for creating the effect of older sonar lines disappearing in a nice gradual way. context.getImageData method returns an array of RGBA values representing the pixels that create current canvas image. The function loops through image data and progressively reduces the intensity of green color component. This way sonar lines fade to black.

And viola - sonar image can be rendered in a browser :)

Isn't it amazing what is now possible on the web platform? I'm not exactly a dinosaur but I remember when displaying a div overlay on a page required use of hidden iframe (because select elements were otherwise rendered above the overlay)... Crazy times ;)

[OoB] Sonar with Arduino, C#, JavaScript and HTML5

This post marks the beginning of "Out of Boredom" series. It will be about creating stuff with my recently purchased Arduino Uno. Let's have a break from chores of professional programming and create something just for fun :)

My first Arduino based project is Sonar. It utilizes ultrasonic range sensor, servo, SignalR and canvas to create sonar image:

Sonar at work... Click to enlarge...

I am splitting the description into two posts. First post will focus on hardware components and Arduino sketch and the second will be about .NET and JavaScript applications. You can get complete code in this GitHub repository. You can also click here to see short video of the whole thing working.

Here are hardware elements used:

Element Role
Arduino Uno R3 Handling HC-SR04, controlling servo and communicating with PC
HC-SR04 Ultrasonic Ranging Module Measuring time it takes sound to bounce back from objects
9g Tower Pro Micro Servo Moving sensor to get 180 degree view
Red LED Signalling ready state
330 Ohm resistor Limiting current going through diode
Breadboard and few jumper wires Connecting components without soldering 

That's it, just a few cheap components! Virtually no electronics skills are required to complete this project. I assume, however, that you have basic Arduino knowledge and you know a bit about C# and JavaScript.

Here is the software stack:

Element Role
Arduino sketch (firmware) Measuring distance, moving servo and sending data to PC over serial port 
.NET/C# 4.5 console application with SignalR library  Receiving data from Arduino using SerialPort class and broadcasting angle and distance information to clients
HTML5 page with JavaScript SignalR library Receives data from server and creates sonar image using canvas element

Above might sound a bit overwhelming but I assure you that the code is short and not that complicated.

The basic idea goes like this: HC-SR04 sensor measures time it takes an ultrasonic signal to bounce from obstacles and this gives as a chance to calculate distance to these obstacles. Position of the sensor is controlled by servo. Information about distance to objects and direction in which the sensor is pointing is sent to PC that is running console application with SignalR sever. PC receives the data and sends it to JavaScript clients that are capable of presenting sonar data in nice visual way using HTML5 canvas element...

More details!

The main component (except for the Arduino of course) is the HC-SR04 Ultrasonic Ranging Module. This sensor works by sending sound signal at 40 kHz (so above human perception limits) and detecting the echo. That's why this project is called "Sonar" and not "Radar" - it uses sound waves (not radio waves) do detect objects. The sensor should work in ranges from 2cm up to 400cm at accuracy of few millimetres. But keep in mind that the shape an material of objects might affect performance. I tested it at maximum distance of about 2 meters and was happy with the results. You can use this sensor without any libraries. That requires doing things like putting HIGH value on Trig pin for 10uS to emit ultrasonic signal, measuring duration of HIGH pulse on Echo pin and calculating distance knowing that speed of sound in the air is around 340m/s... But there's a better way: you can use NewPing lib (link) to get the distance. If you don't know how to include new library in your Arduino sketch click here.

The second important component is the servo. HC-SR04 sensor has measuring angle of about 15 degrees. But if we move it around by attaching it to servo's arm we can easily get 180 degree view. I won't get into details on how servo works and how it is controlled in this post. I plan to make another post about shooting paintball marker with Arduino+laptop and I will describe it then. For now all you need to know is that Arduino comes with Servo library which makes it very easy to move servo into desired position (angle)... I utilized 9g Tower Pro Micro Servo in this project. It's powerful enough to move the sensor yet can be powered directly from Arduino's +5V pin.

Last physical components are LED used to signal the ready state (that is when setup function had completed) with its accompanying resistor. Making a diode shine is electronics equivalent of "Hello World!" so I'm sure you know how to handle LED. Even if not, you can always use the tiny built-in LED connected to pin 13 of Arduino Uno...

This diagram shows how hardware components should be connected:

Fritzing breadboard diagram

Here's the whole code that should be uploaded to Arduino:  

#include <NewPing.h>
#include <Servo.h>  

const byte setupReadyLedPin = 8;
const byte triggerPin = 10;
const byte echoPin = 11;
const byte servoPin = 12;

const byte maxDistanceInCm = 100;

byte angle;
byte angleStep;
byte angleStepDelayInMs = 50;

NewPing sonar(triggerPin, echoPin, maxDistanceInCm); 
Servo servo; 

void setup() {  
    pinMode(setupReadyLedPin, OUTPUT);
    angle = 0;
    angleStep = 1;
    Serial.begin(9600); // Open connection with PC
    digitalWrite(setupReadyLedPin, HIGH);

void loop() {      
    angle += angleStep;
    servo.write(angle); // Move servo

void alterServoMoveDirection() {
    if (angle == 180) {
       angleStep = -1; 
    } else if (angle == 0) {
       angleStep = 1;

void measureAndSendDistance() {
    byte distanceInCm = sonar.ping_cm(); // Use ultrasound to measure distance   
    byte sonarData[] = {255, angle, distanceInCm};
    Serial.write(sonarData, 3); // Send data to PC

As stated before, I assume that you know something about Arduino programming and things like const, pinMode, delay, setup and loop don't require explanation...

First lines which should capture your attention are:

#include <NewPing.h>
#include <Servo.h>  

NewPing sonar(triggerPin, echoPin, maxDistanceInCm); 
Servo servo;

Above lines let us use NewPing and Servo classes to measure distance and move the sensor. Notice also that setup function has such lines:


These exist to set the pin used to control the servo and to move the servo into initial position at 0 degrees.

This line:


allowes Arduino to talk to PC (in my case a laptop with Windows 7) over serial port. That's right, even though Arduino Uno is connected to computer via USB cable it actually uses COM port to communicate. On my machine its called "COM3" (screen shown below comes from Device Manager - my Windows is in Polish):

COM port for Arduino... Click to enlarge...

The value passed to begin method determinates baud rate (communication speed). It's important to have the same value used in software that communicats with Arduino.

The loop function moves servo and invokes measureAndSendDistance function which uses NewPing to calculate distance and Serial to send data to PC. This is how easy it is to get distance in cm thanks to NewPing lib:

byte distanceInCm = sonar.ping_cm()

If measured distance exceeds the maximum value specified as last parameter to NewPing constructor the value of 0 is returned. Check NewPing docs to see other useful functions of this lib.

And finally this is how Arduino sends data to PC:

byte sonarData[] = {255, angle, distanceInCm};
Serial.write(sonarData, 3); // Send data to PC

The first array element (255) is used as a marker/separator to easily distinguish pairs of angle-distance values. Its role will become clear in the second post which will describe SignalR server and clients... I assume that maxDistanceInCm const will never be set above 200 so distanceInCm will never have value of 255. 255 will never be sent as an angle too because our servo moves in 0..180 degrees range. Sure it might be a good idea to create const and avoid 255 magic number. Some validation would be useful too... But screw it, this project is just for fun! :)

Ok, you survived to the end of the first post about Arduino/.NET/JS/HTML sonar. The second post should be ready in about a week.

Update 2014-09-29: Here's the Part 2.

TortoiseSVN pre-commit hook in C# - save yourself some troubles!

Probably everyone who creates or debugs a program happens to make temporary changes to the code that make current task easier but should never get into the repository. And probably everyone has accidentally put such code into next revision. If you are lucky enough, mistake will be revealed quickly and the only result will be a bit of shame, if not...

If only there was a way to mark “uncommitable” code...

You can do it and it’s pretty simple!

TortoiseSVN lets you set so-called pre-commit hook. It’s a program (or script) that is run when user clicks “OK” button in “SVN Commit” window. Hook can for example check content of modified files and block commit when deemed appropriate. Tortoise hooks differ from Subversion hooks in that they are executed locally and not on the server that hosts the repository. You therefore don’t have to worry whether your hook will be accepted by the admin or if it works on the server (e.g. server may not have .NET installed), you also don’t affect the experience of other users of the repository. Client-side hooks are quicker too.

Detailed description of hooks can be found in „4.30.8. Client Side Hook Scripts” chapter of Tortoises help file.

Tortoise supports 7 kinds of hooks: start-commit, pre-commit, post-commit, start-update, pre-update, post-update and pre-connect. We are concerned with pre-commit action. The essence of the hook is to check whether one of added or modified files contains temporary code marker. Our marker may be a “NOT_FOR_REPO” text put into a comment placed above temporary code.

This is whole hook’s code – simple console application, that may save your ass :)

using System;
using System.IO;
using System.Text.RegularExpressions;

namespace NotForRepoPreCommitHook
    class Program
        const string NotForRepoMarker = "NOT_FOR_REPO";

        static void Main(string[] args)
            string[] affectedPaths = File.ReadAllLines(args[0]);

            Regex fileExtensionPattern = new Regex(@"^.*\.(cs|js|xml|config)$", RegexOptions.IgnoreCase);

            foreach (string path in affectedPaths)
                if (fileExtensionPattern.IsMatch(path) && File.Exists(path))
                    if (ContainsNotForRepoMarker(path))
                        string errorMessage = string.Format("{0} marker found in {1}", NotForRepoMarker, path);

        static bool ContainsNotForRepoMarker(string path)
            StreamReader reader = File.OpenText(path);

                string line = reader.ReadLine();

                while (line != null)
                    if (line.Contains(NotForRepoMarker))
                        return true;

                    line = reader.ReadLine();

            return false;

TSVN calls pre-commit hook with four parameters. We are interested only in the first one. It contains a path to *.tmp file. In this file there is a list of files affected by current commit. Each line is one path. After loading the list, files are filtered by extension (useful if you don’t want to process files of all types). Checking if file exists is also important – the list from *.tmp file contains paths for deleted files too! Detection of the marker represented by NotForRepoMarker constant is realized by ContainsNotForRepoMarker method. Despite its simplicity it provides good performance. On mine (middle range) laptop, 100 MB file takes less than a second to process. If marker is found, program exits with error code (value different than 0). Before quitting, information about which file contains the marker is sent to standard error output (via Console.Error). This message will get displayed in Tortoise window.

The code is simple, isn’t it? In addition, hook installation is also trivial!

To attach hook, choose “Settings” item from Tortoise’s context menu. Then select “Hook scripts” element and click “Add…” button. Such window will appear:

TSVN hooks configuration window

Set „Hook Type” to „Pre-Commit Hook”. Fill “Working Copy Path” field with a path to the directory that contains local copy of the repo (different folders can have different hooks). In “Command Line To Execute” field, set path to the application that implements the hook. Check “Wait for the script to finish” and “Hide the script while running” options (the latter will prevent console window from showing). Press “OK” button and voila, hook is installed!

Now mark some code with “NOT_FOR_REPO” comment and try to execute commit. You should see something like that:

Operation blocked by pre-commit hook

Notice the „Retry without hooks” button – it allows commit to be completed by ignoring hooks.

We now have a hook that prevents from temporary code submission. One may also want to create a hook that enforces log message to be filled, blocks *.log files commits etc. Your private hooks – you decide! And if some of the hooks will be usefull for the whole team, you can always remake them as Subversion hooks.

Tested on TortoiseSVN 1.7.8/Subversion 1.7.6.

Update 24.03.2014: Added emphasis to checking "Wait for the script to finish" option - without it hook will not block commits!

Update 17.09.2013: (additional info): You may set hook on a parent folder which contains multiple repositories checkouts. If you are willing to sacrifice a bit of performance for added protection you may resign from filtering files before checking for NotForRepoMarker marker.