A Better Sample For The Netduino ShieldStudio 4-digit Shield

I recently started working with the Netduino microcontroller and one of the initial projects I decided to tackle was creating a better sample for a LED matrix shield. It wasn’t really complicated – overall, it took me around an hour to put everything together and test it on a real device.

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Here are some things that I added to the updated sample:

• Automatically initialize the I2CDevice instance when the LEDMatrix class is instantiated.
• Perform the device setup automatically on class instantiation
• Ability to write a single character in one matrix slot with additional effects (ShortBlink or LongBlink)
• Ability to directly write a string instead of passing single characters
• Support of different ways a string can de displayed (MarqueeRight, MarqueeLeft, Blocks)
• Built-in references for some special characters (e.g. currency symbols, arrow up, arrow down)
• Support for writing inverted characters (inverted background/foreground)

That being said, a simple snippet that would allow the user to pass a string would look like this:

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LEDMatrix matrix = new LEDMatrix(0×50, 400); 
matrix.Clear();
matrix.WriteString("Hello from my sample!", StringEffect.MarqueeRight);

Special symbols are introduced simply to reduce the amount of work needed to look for special characters. A simple for loop from 0 to 255 will reveal most of the characters that cannot be introduced from the keyboard in a single tap, if needed. The characters I included in the SpecialCharacters enum are the most useful for me.

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Special blinking effects for characters are taking place “one slot at a time” due to the single-threaded nature of the Netduino CPU. This can be modified with a Timer and preserved object state, but for now I needed sequential blinking so this does the job perfectly.

Inverted characters are calculated by adding 128 to the default character byte value (according to the ASCII table – decimal) for alphanumeric characters and some symbols. The inverted version for the characters represented in the image above would look like this:

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This is more of a “just for fun” class, but it extends the default sample to show some basic capabilities out of the box. You can download the ZIP here (link no longer available).

Here is a video of the class in action:

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Requirements:

• Microsoft Visual C# Express 2010
• .NET Micro Framework 4.1 (used as the solution target)
• Netduino (either basic or Plus – both work fine)
• SheildStudio 4-digit LED Matrix shield