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.

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