Embedded Developer

I suppose every journey starts with a single step, and often a small step at that.  Relearning the skills of yesteryear will be no different.  I’m slowly working myself up to controlling the LED from the Netduino Plus.  On this basis I’ll be taking it steady and tackle this in three parts:

1. Light a LED from a 3.3V power supply
2. Use a transistor as a switch to control the LED circuit above (more here)
3. Use the Netduino Plus to control the transistor/LED circuit

The reason for taking this slowly is the Netduino Plus can only supply a small amount of current and I’m taking care to draw as little current as possible whilst still having a usable project.

So step one, a simple LED circuit from a static power supply

The design is simple (I’m not taxing myself too much) and requires little more knowledge that that provided by the LED data sheet and Ohms Law.  The task is to use a stable 3.3V power supply and use this to light up a red LED.  Minor complication here, I don’t have the datasheet for the LED so I’m not sure how much current it will take.  A quick search on Google provides a whole list of web sites with information on LEDs and the consensus of opinion is that modern red LEDs draw about 20mA max and have a typical voltage drop of around 2.5V (along with one comment that burning LEDs make a rather unpleasant smell).

Note 8 Jan 2011: Finally found the data sheet for the red LED being used and V_f = 2.5V and I_f = 20 mA.

Armed with this information I need to include a series resistor in the circuit to take the additional voltage drop and limit the current.

And for the calculations:

Working on the resistor we get the following:

Now this resistor is not available as a standard component.  The nearest ones are 39 ohms and 43 ohms.  A quick look through my supply and I’ve got 33 ohms and 47 ohms.  So I plump for the 47 ohms and the circuit becomes:

The power supply itself will come from a breadboard power supply stick from Cool Components.

Theory over, now for the application

First job is to solder a couple of male header row connectors to the power supply to make it easier to connect to the power supply to the breadboard.  Next add the resistor and the LED and plug it all in.

The good news is it didn’t go bang and no hint of the smell of burning LEDs.  In fact it worked, one glowing red LED.

A quick check with the multi-meter revealed that

1. The power supply is in fact delivering 3.25V and not the rated 3.3V.
2. The voltage drop over the series resistor was 1.25V which means the circuit is drawing 26mA and the voltage drop across the LED is in fact only 2V.

All in all a small and simple first step.

Christmas is finally over and a new year is on its way.  Before you turn off this is not a retrospective of the past year and a list of promises (which will be broken) for the new year.  Instead a note that I’ll probably be relearning some long lost skills, namely basic electronics as Christmas saw a small but welcome present – a Netduino Plus.  My only hope is that I’ll get up to speed quickly enough and don’t burn it out.

All the best for 2011.

So it has been a week or so since Visual Studio 2010 was released in the wild and the verdict is that it is a great step forward.  It is amazing how simple things like pinable data tips make your life as a developer a lot easier.

One thing I have found irritating is the fact that you need Sharepoint installed in order to use the reporting facilities in Team Foundation Server (TFS).  This is not so much of a problem in a team environment as you are normally using servers to host TFS but it is a bind in a single developer environment.  For those of you who are not aware, Sharepoint will not install on Vista or Windows 7 running on a 32 bit machine.  This is a problem for me when experimenting as the environment where I test my ideas before implementing them is Windows 7 32-bit.  Looks like I’ll be rebuilding an old 64-bit machine in the near future.  On the up side, it will allow me to look at Sharepoint 2010 which has recently been added to MSDN.  As I say, all developers like new toys :).

Update: 25/04/2010

A recent blog posing by Shai Raiten suggests that Sharepoint can be installed on Windows 7 32-bit.  At the end of the post it suggested that an advanced installation was possible (note the Advanced button is highlighted) but this generated several errors.  I have since read the full article on Bamboo Solutions web site and followed their instructions and I now have WSS3.0 SP1 installed on my laptop.  Now all I have to do is get the reporting services working.

The Firestarter event held at the start of this month saw Microsoft announce the future release of Silverlight 5.  A run down of some of the new features can be found here on John Papa’s blog.  There is a also a link to the video of Scott Guthrie’s keynote.

Microsoft have released a training kit for Silverlight 4.  This is available online (through Channel 9) or as an offline download.

Thursday this week found me attending a technical community day just outside Leeds.  The event was organised by Black Marble and covered the recent Visual Studio 2010 launch.  The morning saw an overview of the tools by Matt Dunn from Microsoft along with a demonstration of Team Foundation Server features and how they integrate into the software development life cycle.  The highlight of the day was a talk by Jesse Liberty covering Silverlight.  Whilst light on technical content his talk was very entertaining covering his introduction to Microsoft and the evolution of Silverlight.  If you get the chance I would recommend that you take the time to attend one of his presentations as he is a very entertaining presenter.

OK, so I’m a day late on this one but then I have had my hands full uninstalling the release candidate and updating to the full version.  A fairly comprehensive overview with links can be found on Scott Gutherie’s blog.

The Express editions can be downloaded from the Microsoft Express Website.

I have to admit it but it has taken me far too long get my web site and this blog sorted out.  The stimulus came with the move to a new hosting provider and the fact that I get the flexibiliy I wanted and the ability to work with the technology I was happiest with.  So here we are, a week later and the blog site is up and running.  I suppose I’ll have to address the web site next.

So, what can we look forward to?  To be honest I don’t know.  There will certainly be a fair amount of technology content along with the odd thing I find amusing and want to share.

All I can say is I’ll keep you posted <groan>