{"id":6392,"date":"2012-12-28T09:54:10","date_gmt":"2012-12-28T14:54:10","guid":{"rendered":"http:\/\/embedded-lab.com\/blog\/?p=6392"},"modified":"2012-12-29T18:38:55","modified_gmt":"2012-12-29T23:38:55","slug":"interfacing-a-character-lcd","status":"publish","type":"post","link":"https:\/\/embedded-lab.com\/blog\/interfacing-a-character-lcd\/","title":{"rendered":"Netduino Day 2: Interfacing a Character LCD"},"content":{"rendered":"

Liquid Crystal Displays (LCD) are a great choice of output device for displaying alphanumeric characters in real time. They are also very useful if your project requires an interactive user interface for data input. Besides, they are inexpensive, consume less power than LED displays, and give a more professional look to your project. Today we will explore how to interface an HD44780 based character LCD to Netduino to display alphanumeric characters. For technical details of the HD44780 driver, please read its datasheet<\/a>\u00a0as well as its\u00a0interfacing example with chipKit<\/a>.<\/p>\n

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Information displayed on Character LCD<\/p><\/div>\n

<\/p>\n

Circuit Setup and Theory<\/h2>\n

Connection wise it\u2019s really simple. The LCD is operated in 4-bit mode, and therefore pins 7 through 10 (D0-D3) of the LCD are unused. The four most significant data bits, D4-D7 (pins 12 through 14), receives LCD data\/command through Netduino I\/O pins 7, 5, 3, and 1, respectively. Similarly, the Register Select (R\/S) and Enable (E) signal lines of the LCD are driven by Netduino I\/O pins 11 and 9, respectively. LCD pins 1, 2, 3, 4, 15 and 16 are related to power supply, contrast adjustment and backlight LED display, and are connected appropriately as shown below. To understand how LCD works, I have to point you to a different document as it is explained better over there. In Interfacing a Character LCD<\/a>,Raj explains about the communication in 4 bit mode and he also talks about the basics of HD44780 LCD driver. For more technical details, see\u00a0Hitachi HD44780U (LCD-II) datasheet<\/a>.<\/p>\n

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Interfacing a HD44780 character LCD with Netduino<\/p><\/div>\n

Connection With Netduino \/ Netduino Plus<\/h2>\n
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Breadboard Connection: Character LCD and Netduino<\/p><\/div>\n

C#.NET Program<\/h2>\n

There are two ways we can look at the program, one in a very simple way and other, obviously, harder way. In simpler way we don\u2019t worry about what\u2019s inside the LCD class<\/em> (or a library) rather use some of the exposed methods or properties. Let\u2019s take a look at the simpler things first.<\/p>\n\n

LCD lcd =<\/span> new<\/span> LCD(<\/span>\n    Pins.<\/span>GPIO_PIN_D11<\/span>, \/\/ RS<\/span>\n    Pins.<\/span>GPIO_PIN_D9<\/span>,  \/\/ Enable<\/span>\n    Pins.<\/span>GPIO_PIN_D7<\/span>,  \/\/ D4<\/span>\n    Pins.<\/span>GPIO_PIN_D5<\/span>,  \/\/ D5<\/span>\n    Pins.<\/span>GPIO_PIN_D3<\/span>,  \/\/ D6<\/span>\n    Pins.<\/span>GPIO_PIN_D1<\/span>,  \/\/ D7<\/span>\n    20<\/span>,                \/\/ Number of Columns<\/span>\n    LCD.<\/span>Operational<\/span>.<\/span>DoubleLIne<\/span>, \/\/ LCD Row Format<\/span>\n    4<\/span>,                 \/\/ Number of Rows in LCD<\/span>\n    LCD.<\/span>Operational<\/span>.<\/span>Dot5x8<\/span>)<\/span>;<\/span>    \/\/ Dot Size of LCD<\/span>\n \nlcd.<\/span>ShowCursor<\/span> =<\/span> true<\/span>;<\/span>\nlcd.<\/span>Show<\/span>(<\/span>"www.Embedded-Lab.comWelcome's you to Netduino Tutorial site.  Happy Learning! :)"<\/span>, 200<\/span>, true<\/span>)<\/span>;<\/span>\nThread.<\/span>Sleep<\/span>(<\/span>1000<\/span>)<\/span>;<\/span> \/\/ reading time for the viewer<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
As you can see we created an instance of LCD<\/em> class and then set some properties to what we like and simply called the Show<\/em> method. There are two Show<\/em> methods, one will display the given text all at once and the other Show<\/em> method will display one letter at a time.<\/p>\n
Now let\u2019s dig into the complex part. There are several libraries out there but I wrote my own to understand what\u2019s cooking inside. Let\u2019s look at the constructor section,<\/p>\n\n
public<\/span> LCD(<\/span>Cpu.<\/span>Pin<\/span> rs, Cpu.<\/span>Pin<\/span> enable,\n    Cpu.<\/span>Pin<\/span> d4, Cpu.<\/span>Pin<\/span> d5, Cpu.<\/span>Pin<\/span> d6, Cpu.<\/span>Pin<\/span> d7,\n    byte<\/span> columns, Operational lineSize, int<\/span> numberOfRows,\n    Operational dotSize)<\/span>\n{<\/span>\n    RS =<\/span> new<\/span> OutputPort(<\/span>rs, false<\/span>)<\/span>;<\/span>\n    Enable =<\/span> new<\/span> OutputPort(<\/span>enable, false<\/span>)<\/span>;<\/span>\n    D4 =<\/span> new<\/span> OutputPort(<\/span>d4, false<\/span>)<\/span>;<\/span>\n    D5 =<\/span> new<\/span> OutputPort(<\/span>d5, false<\/span>)<\/span>;<\/span>\n    D6 =<\/span> new<\/span> OutputPort(<\/span>d6, false<\/span>)<\/span>;<\/span>\n    D7 =<\/span> new<\/span> OutputPort(<\/span>d7, false<\/span>)<\/span>;<\/span>\n \n    Columns =<\/span> columns;<\/span>\n    DotSize =<\/span> (<\/span>byte<\/span>)<\/span>dotSize;<\/span>\n    NumberOfLines =<\/span> (<\/span>byte<\/span>)<\/span>lineSize;<\/span>\n    NumberOfRows =<\/span> numberOfRows;<\/span>\n \n    Initialize(<\/span>)<\/span>;<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
In the constructor section, it basically creates some Outport<\/em>, saves the LCD<\/em> properties and then calls the Initialize<\/em> method. In this method, we set visual properties, initialize some arrays and then prepare the LCD for 4 bit communication mode.<\/p>\n\n
private<\/span> void<\/span> Initialize(<\/span>)<\/span>\n{<\/span>\n    \/\/initialize fields<\/span>\n    isVisible =<\/span> true<\/span>;<\/span>\n    showCursor =<\/span> false<\/span>;<\/span>\n    isBlinking =<\/span> false<\/span>;<\/span>\n \n    rowAddress =<\/span> new<\/span> byte<\/span>[<\/span>]<\/span> {<\/span> 0x00, 0x40, 0x14, 0x54 }<\/span>;<\/span>\n    firstHalfAddress =<\/span> new<\/span> byte<\/span>[<\/span>]<\/span> {<\/span> 0x10, 0x20, 0x40, 0x80 }<\/span>;<\/span>\n    secondHalfAddress =<\/span> new<\/span> byte<\/span>[<\/span>]<\/span> {<\/span> 0x01, 0x02, 0x04, 0x08 }<\/span>;<\/span>\n \n    currentRow =<\/span> 0<\/span>;<\/span>\n    dirtyColumns =<\/span> 0<\/span>;<\/span>\n \n    Thread.<\/span>Sleep<\/span>(<\/span>50<\/span>)<\/span>;<\/span> \/\/ must wait for a few milliseconds<\/span>\n \n    \/\/ RS to high = data transfer<\/span>\n    \/\/ RS to low = command\/instruction transfer<\/span>\n    RS.<\/span>Write<\/span>(<\/span>false<\/span>)<\/span>;<\/span>\n \n    \/\/ Enable provides a clock function to synchronize data transfer<\/span>\n    Enable.<\/span>Write<\/span>(<\/span>false<\/span>)<\/span>;<\/span>\n \n    \/\/ Set for 4 bit model<\/span>\n    Write(<\/span>0x03, secondHalfAddress)<\/span>;<\/span>\n    Thread.<\/span>Sleep<\/span>(<\/span>4<\/span>)<\/span>;<\/span>\n    Write(<\/span>0x03, secondHalfAddress)<\/span>;<\/span>\n    Thread.<\/span>Sleep<\/span>(<\/span>4<\/span>)<\/span>;<\/span>\n    Write(<\/span>0x03, secondHalfAddress)<\/span>;<\/span>\n    Thread.<\/span>Sleep<\/span>(<\/span>150<\/span>)<\/span>;<\/span>\n    Write(<\/span>0x02, secondHalfAddress)<\/span>;<\/span>\n \n    \/\/ Set the LCD properties<\/span>\n    byte<\/span> operationalValue =<\/span> (<\/span>byte<\/span>)<\/span>(<\/span>(<\/span>byte<\/span>)<\/span>Operational.<\/span>FourBit<\/span> |<\/span> (<\/span>byte<\/span>)<\/span>NumberOfLines |<\/span> (<\/span>byte<\/span>)<\/span>DotSize)<\/span>;<\/span>\n    SendCommand(<\/span>(<\/span>byte<\/span>)<\/span>(<\/span>(<\/span>byte<\/span>)<\/span>Command.<\/span>Operational<\/span> |<\/span> operationalValue)<\/span>)<\/span>;<\/span>\n \n    UpdateDisplayOptions(<\/span>)<\/span>;<\/span>\n \n    ClearDisplay(<\/span>)<\/span>;<\/span>\n \n    byte<\/span> entranceValue =<\/span> (<\/span>byte<\/span>)<\/span>Entrance.<\/span>FromLeft<\/span> |<\/span> (<\/span>byte<\/span>)<\/span>Entrance.<\/span>ShiftDecrement<\/span>;<\/span>\n    SendCommand(<\/span>(<\/span>byte<\/span>)<\/span>(<\/span>(<\/span>byte<\/span>)<\/span>Command.<\/span>Entrance<\/span> |<\/span> entranceValue)<\/span>)<\/span>;<\/span>\n \n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Now, let\u2019s look at the methods that are critical to show the text to the LCD. The first Show<\/em> method allows us to show the given text letter by letter as you can see the loop is structured for each character in the given text.<\/p>\n\n
public<\/span> void<\/span> Show(<\/span>string<\/span> text, int<\/span> delay, bool<\/span> newLine)<\/span>\n{<\/span>\n    if<\/span> (<\/span>newLine)<\/span> dirtyColumns =<\/span> 0<\/span>;<\/span>\n    foreach<\/span> (<\/span>char<\/span> textChar in<\/span> text.<\/span>ToCharArray<\/span>(<\/span>)<\/span>)<\/span>\n    {<\/span>\n        ResetLines(<\/span>)<\/span>;<\/span>\n        Show(<\/span>Encoding.<\/span>UTF8<\/span>.<\/span>GetBytes<\/span>(<\/span>textChar.<\/span>ToString<\/span>(<\/span>)<\/span>)<\/span>)<\/span>;<\/span>\n        dirtyColumns +=<\/span> 1<\/span>;<\/span>\n        Thread.<\/span>Sleep<\/span>(<\/span>delay)<\/span>;<\/span>\n    }<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
The second Show<\/em> method basically shows the whole text at once but before that it does some formatting so that the text will appear continuously. Trust me showing given text in a continuous way is one of the difficult part that I resolved in this LCD<\/em> class<\/em>.<\/p>\n\n
public<\/span> void<\/span> Show(<\/span>string<\/span> text)<\/span>\n{<\/span>\n    string<\/span>[<\/span>]<\/span> splitedText =<\/span> SplitText(<\/span>text)<\/span>;<\/span>\n    Show(<\/span>splitedText)<\/span>;<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Finally, the method that writes information to the LCD is done under Write<\/em> method. The first Write<\/em> method calls the send Write<\/em> method it passes the write value and the address where to send the information. The second Write<\/em> method basically writes the information to the LCD.<\/p>\n\n
private<\/span> void<\/span> Write(<\/span>byte<\/span>[<\/span>]<\/span> data)<\/span>\n{<\/span>\n    foreach<\/span> (<\/span>byte<\/span> value<\/span> in<\/span> data)<\/span>\n    {<\/span>\n        Write(<\/span>value<\/span>, firstHalfAddress)<\/span>;<\/span> \/\/ First half<\/span>\n        Write(<\/span>value<\/span>, secondHalfAddress)<\/span>;<\/span> \/\/ Second half<\/span>\n    }<\/span>\n}<\/span>\n \nprivate<\/span> void<\/span> Write(<\/span>byte<\/span> value<\/span>, byte<\/span>[<\/span>]<\/span> halfAddress)<\/span>\n{<\/span>\n    D4.<\/span>Write<\/span>(<\/span>(<\/span>value<\/span> &<\/span>amp;<\/span> halfAddress[<\/span>0<\/span>]<\/span>)<\/span> &<\/span>gt;<\/span> 0<\/span>)<\/span>;<\/span>\n    D5.<\/span>Write<\/span>(<\/span>(<\/span>value<\/span> &<\/span>amp;<\/span> halfAddress[<\/span>1<\/span>]<\/span>)<\/span> &<\/span>gt;<\/span> 0<\/span>)<\/span>;<\/span>\n    D6.<\/span>Write<\/span>(<\/span>(<\/span>value<\/span> &<\/span>amp;<\/span> halfAddress[<\/span>2<\/span>]<\/span>)<\/span> &<\/span>gt;<\/span> 0<\/span>)<\/span>;<\/span>\n    D7.<\/span>Write<\/span>(<\/span>(<\/span>value<\/span> &<\/span>amp;<\/span> halfAddress[<\/span>3<\/span>]<\/span>)<\/span> &<\/span>gt;<\/span> 0<\/span>)<\/span>;<\/span>\n \n    Enable.<\/span>Write<\/span>(<\/span>true<\/span>)<\/span>;<\/span>\n    Enable.<\/span>Write<\/span>(<\/span>false<\/span>)<\/span>;<\/span>\n    \/\/Debug.Print("Wrote " + value.ToString());<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Output<\/h2>\n
After connecting a few wires, when you run your code and visualize the text that you wanted, puts smile in your face. Depending upon which Show<\/em> method you are using will give you get different results, one will show letter by letter and other will show whole text at once. As in the video, when you rotate the potentiometer, the display contrast changes.<\/p>\n
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Character LCD, ready to take input<\/p><\/div>\n
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Output on Character LCD showing digits and alphabets<\/p><\/div>\n
A small Video based on the following code:<\/p>\n\n
lcd.<\/span>ShowCursor<\/span> =<\/span> true<\/span>;<\/span>\nlcd.<\/span>Show<\/span>(<\/span>"www.Embedded-Lab.comWelcome's you to Netduino Tutorial site.  Happy Learning! :)"<\/span>, 200<\/span>, true<\/span>)<\/span>;<\/span>\nThread.<\/span>Sleep<\/span>(<\/span>1000<\/span>)<\/span>;<\/span> \/\/ reading time for the viewer<\/span>\n \nlcd.<\/span>ClearDisplay<\/span>(<\/span>)<\/span>;<\/span>\nlcd.<\/span>Show<\/span>(<\/span>"That was cool! Let's clear the display and show all text at once"<\/span>, 200<\/span>, true<\/span>)<\/span>;<\/span>\nThread.<\/span>Sleep<\/span>(<\/span>1000<\/span>)<\/span>;<\/span> \/\/ reading time for the viewer<\/span>\n \nlcd.<\/span>ClearDisplay<\/span>(<\/span>)<\/span>;<\/span>\nlcd.<\/span>ShowCursor<\/span> =<\/span> false<\/span>;<\/span>\nlcd.<\/span>Show<\/span>(<\/span>"ABCDEFGHILKLMnopqrstuvwxyz0123456789                              -Thanks!"<\/span>)<\/span>;<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n