Programming the ATmega168

There are several ways to get your program onto an ATmega168, the way I'm doing it is with one of these programmers and some jumper wires  - essentially I followed the SparkFun tutorial here.  This is something that I'm working on at the moment:

 

But you could also use one of these Olimex development boards, which is another way I have tried (and means that you can dispense with all those jumper wires).

The AVR pocket programmer is good because pretty much any PC has USB these days (you can also use serial or parallel ports to program an ATmega).  But the pocket programmer can also provide a 5v power supply from USB.

If you want to build your own programmer (which would probably be the cheapest option) then take a look that this, which should get you able to build a programmer for the cost of some wire, resistors and a parallel port connector (assuming that you have a PC with a parallel port).  For me, I found it easiest to just buy something from SparkFun.  In my experience the pocket programmer only works when attached to a USB hub, I've never managed to get it to work when plugged directly into the USB port of my PC - I've never bothered to find out why.

Of course, the other thing you'll need is a development tool, so that you can compile your source code and get the resulting output file copied to the processor.  I'm using WinAVR, or more specifically the portable version which is here.  The portable version means that I can put my development environment on a memory stick and use it on whatever computer I happen to be sat in front of.  Very nifty.

So when you're armed with 1) a programmer, and 2) a copy of WinAVR ...you should be ready to go.  You'll need some code to compile!  I'm going to post that next.

Optimising StringBuilder Appending

I have been working on some C# code optimisation, for speed.  The code in question does a lot of work with strings, so we already use StringBuilder to make it more efficient.  But what is the fastest way to append stuff to the StringBuilder?  In this instance, we're building a lot of comma seperated lists, and even with StringBuilder there are several ways, for example:

 

Method 1, AppendFormat:

sb.AppendFormat("{0},",myStr);

 

Method 2, Multiple Append:

sb.Append(myStr);

sb.Append(",");

 

Method 3, Multiple Append (with a comma already in a string):

string sep = ",";

...

sb.Append(myStr);

sb.Append(sep);

 

Method 4, Single Append:

sb.Append(myStr+sep);

 

... so I decided to check it out.  Here are the results (in seconds), after using each technique one hundred million times (I did five tests and then averaged the results):

 

 

#1

#2

#3

#4

#5

Average

1 AppendFormat

17.20

17.56

17.36

17.58

17.55

17.45

2 Multiple Append

6.61

7.27

6.70

7.27

7.28

7.03

3 Multiple Append (comma in string)

6.65

7.20

6.75

7.20

7.20

7.00

4 Single Append

8.13

8.34

8.31

8.34

8.34

8.29

 

I was quite surprised at how much slower AppendFormat was (although I can understand why).  But it's also worth remembering that the lazy coders way of using a single Append with the + operator to attach the comma is quite a bit slower than calling two Append methods (again, you can understand why when you think about it).

 

Here is the code that I used to test:

 

static void Main(string[] args)

{

    DateTime start = DateTime.Now;

    StringBuilder sb = new StringBuilder();

    string myStr = "hi";

 

    for (int t = 0; t < 100000000; t++)

    {

        sb.AppendFormat("{0},",myStr);

        if ((t % 1000)==0) sb.Remove(0, sb.Length - 1); 

    }

    TimeSpan gap = DateTime.Now - start;

    Console.WriteLine("AppendFormat takes: {0}", gap);

    sb.Remove(0, sb.Length - 1);

 

    start = DateTime.Now;

    for (int t = 0; t < 100000000; t++)

    {

        sb.Append(myStr);

        sb.Append(",");

        if ((t % 1000) == 0) sb.Remove(0, sb.Length - 1);

    }

    gap = DateTime.Now - start;

    Console.WriteLine("Multiple Appends takes: {0}", gap);

    sb.Remove(0, sb.Length - 1);

 

    string sep = ",";

    start = DateTime.Now;

    for (int t = 0; t < 100000000; t++)

    {

        sb.Append(myStr);

        sb.Append(sep);

        if ((t % 1000) == 0) sb.Remove(0, sb.Length - 1);

    }

    gap = DateTime.Now - start;

    Console.WriteLine("Multiple Appends (comma in string) takes: {0}", gap);

    sb.Remove(0, sb.Length - 1);

 

    start = DateTime.Now;

    for (int t = 0; t < 100000000; t++)

    {

        sb.Append(myStr+sep);

        if ((t % 1000) == 0) sb.Remove(0, sb.Length - 1);

    }

    gap = DateTime.Now - start;

    Console.WriteLine("Single Append (comma in string) takes: {0}", gap);

    sb.Remove(0, sb.Length - 1);

 

    Console.ReadKey(); 

}

Sorting a jagged array

This week, I had a need to sort a jagged array of integers, and this is the solution that I came up with:

 

public class IntArraySorter

{

    public static void ExampleSorting()

    {

        int[] a = new int[5] { 1,2,3,4,0 };

        int[] b = new int[4] { 1,2,3,0 };

        int[] c = new int[3] { 1,2,0 };

        int[] d = new int[2] { 1,0 };

        int[] e = new int[1] { 1 };

 

        // sort a 2 dimensional array of integers

        int[][] multi = new int[5][] {a,b,c,d,e};

        Array.Sort(multi, CompareIntArrays);

 

        // we can also use it to sort a List of integer arrays

        List<int[]> list = new List<int[]>();

        list.AddRange(new int[][] {a,b,c,d,e });

        list.Sort(CompareIntArrays);

        int your_breakpoint_here = 0;

    }

 

    public static int CompareIntArrays(int[] x, int[] y)

    {

        int length = x.Length > y.Length ? x.Length : y.Length;

        int diff = 0;

        for (int t = 0; t < length; t++)

        {

            diff = safeGet(x, t) - safeGet(y, t);

            if (diff != 0) return diff;

        }

        return x.Length - y.Length;

    }

    private static int safeGet(int[] arr, int element)

    {

        return (element > arr.Length - 1) ? 0 : arr[element];

    }

}

 

...this technique will work with 2 dimensional arrays of integers if they are jagged or not.  So I thought that it was the type of thing that was worth posting up here for future reference.

Improved Annoyatron Schematic

I have been starting to learn to use Eagle, so that I can document my circuit diagrams.  Being quite new to designing hardware I'm learning that it's not good enough to just keep a copy of the source code anymore!  So, here is the very simple circuit that makes up my improved Annoyatron:

It's very simple to knock this up on a small breadboard, you just need the ATMega168, a speaker and a battery, just like this:

Obviously, the ATmega168 is overspecified, but I have a few of them and it's easier to mess around with one type of processor.  I really will try to post the source code and some notes on how to get the source code onto the processor as a program.  Honest.

New Soldering Iron

I've just bought one of these soldering irons.  I don't know why I didn't do it ages ago!  It's been useful since I've been taking things apart again, for example here is an infrared receiver that I've just removed from an old set-top box:

de-soldered IR receiver

The new iron made a nice job of it, I set the temperature to a reasonably high level and heated the pins at the back of the board whilst tugging the otherside with a pair of pliers.  Each pin came away very easily.  I've only had it for a day, but so far it has been fantastic.  Plus it's great to have an iron without a power cable, it's much less fiddly.

Windows 7 has arrived!

It's here!  Finally, Lenovo have sent my upgrade.  It installed without a hitch and I'm very pleased with my new OS.  They never did answer any of my recent e-mails chasing it up though.

Lenovo the third

OK, so I thought that I was finally making some progress with my "free" Windows 7 upgrade that comes with my new Lenovo PC.  It took a very long time for them to validate my purchase - they check to see that you really have bought a Lenovo PC that qualifies for the free upgrade.  I have no problem with that, but why did it take so long? In the end they validated my purchase 44 days after I registered for the upgrade.

So now they have actually taken my money, yes that’s right there is a £16 "shipping" charge.  Don’t get me started – it does not cost £16 to send out a piece of software.  Anyway, I have paid, they have taken the money off my card.  In fact, they took the money 12 days ago.  Their e-mail confirming the payment said: "A notification email with the shipping details will be sent to you when your order has been shipped".  Guess what?  Nothing.   So they have taken my £16 and not shipped anything.  So I thought that I would drop them a line via their Windows 7 Upgrade website.  So far all I have got is an automated response: "This is to acknowledge the receipt of your enquiry and you will hear from us within 10 business days".  Whoa! Two weeks to answer an e-mail?  What’s interesting is that before they took my money their responses said: "This is to acknowledge the receipt of your enquiry and you will hear from us within 1-3 business days".  Fascinating how they lose interest in you once they have taken your money, eh?

Running the ATmega168

...so like me you've gone and got an ATmega168 from somewhere like http://www.sparkfun.com (which is where I get a lot of my stuff).  It probably cost you about £2.50. Obviously you'd like to get it to do something meaningful, so what do you need to do?  Take a look at this pinout for the processor:

Drop the processor into a breadboard, making sure that it straddles the middle row.  All we need to do is connect pins 1, 7 and 20 to a +5v DC supply and pins 8 and 22 to Ground.  That's all there is to it.  It's useful to note that the purpose of supplying power to pin 1 is to tell the microprocessor that it is not being reset.  Not supplying power to this pin will prevent any code from running, it will remain in reset mode.  We could use this pin like a reset button on a PC by adding a button and a resistor, but we won't worry about that right now.  I'm saying use a 5v supply because it's a nice easy voltage to find (for example, USB will supply 5v with 1A current, which is fine), but the processor should work with a supply between 2.7v and 5.5v (see the datasheet here if you're interested).  I often use a spare PC power supply, because they normally have a 5v output and are not expensive.

 

OK, so the processor may be running - but we've not put any code onto it yet.  So that's the next thing on our todo list.

Improved annoyatron

I think that it's good to keep your hand in with some plain old C programming once in a while.  So I ocasionally mess around with microprocessors. I've been working on an improved annoyatron, with my version it will pretend to be a mobile phone - by playing a simple ringtone. This is what it currently looks like:

annoyatron 2.0

 I've used an AVR ATmega168 microprocessor, which is over spec, but I had a couple of them lying around.  In fact all of the other components except for the button cell battery and holder were things that I had sitting around.  What tends to happen is that before I throw anything away, I take it to bits to see if I can remove anything.  Even a salvaged switch can be useful one day.  And it's fun to take stuff apart :-)

So ... what I'll try to do is post more about this - what development tools I've used and what I have discovered along the way.  I'll be sure to refer back to it if nobody else does.

Tron Legacy

My wife told me that they were making a new Tron movie (the original came out in 1982) but even better than that, Daft Punk are doing the soundtrack. Sounds good, I really hope they don't mess this film up. So of course, I had to try and find a trailer, which I found here:
http://www.youtube.com/watch?v=a1IpPpB3iWI

Looks good so far. But then I also went and found this: http://www.youtube.com/watch?v=TbBH3bNyge4 it's rework but still cool, Daft Punk are probably still fiddling with it anyway.  But I can't wait to hear the other stuff that they come up with, I think I'm gonna like it...