{"id":6395,"date":"2013-01-17T21:50:03","date_gmt":"2013-01-18T02:50:03","guid":{"rendered":"http:\/\/embedded-lab.com\/blog\/?p=6395"},"modified":"2013-01-28T13:52:31","modified_gmt":"2013-01-28T18:52:31","slug":"day-3-seven-segments-led-with-an-ldr","status":"publish","type":"post","link":"https:\/\/embedded-lab.com\/blog\/day-3-seven-segments-led-with-an-ldr\/","title":{"rendered":"Netduino Day 3 – Multiplexed Seven-Segment LED displays"},"content":{"rendered":"

A visual output always adds value to any project. In this third day tutorial, we are going to display some numeric, alphabetic as well as two symbolic characters on a 4-digit seven segment LED module. The way we are interfacing the seven segments LEDs is known as multiplexing, which allows to save some I\/O pins of Netduino as compared to driving them individually. The seven segment LEDs are resource and power hungry, but we are going to do this experiment just to get our feet wet in the microcontroller or embedded world and to understand the basics of a seven segments LED displays.<\/p>\n

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Seven Segments LED displaying Letter 'A'<\/p><\/div>\n

In today’s experiment, we are going to read an analog voltage from an LDR sensor and display the ADC output on to four seven segment LEDs. As you might know seven segments LED is made with seven plus one LEDs. Each LED has its own name as we can see in the picture. To display digit \u201c1\u201d, we need to send high signal to the LED \u2018b\u2019 and \u2018c\u2019 only and ground the cathode. Now, let\u2019s say we need to display \u201c12\u201d. The way we do is, we display \u201c1\u201d in one of LED unit then turn it off then we will display \u201c2\u201d in our second LED unit then turn it off too but we will turn on the first one. So, we will cycle the display of each letter in a loop resulting in the entire digit that we like to display. This basically is the multiplexing.<\/p>\n

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Seven Segments LEDs Names<\/p><\/div>\n

Circuit Setup and Theory<\/h2>\n

In this tutorial also, we can split our connections into two categories, Analog and Digital. In analog section, we have used an LDR as our analog input device. With the illumination, the resistance of the LDR will change causing change in voltage. This type of connection is sometime referred as voltage divider. The drop or rise in voltage across the LDR will be an input for our analog pin.<\/p>\n

In the digital section, connections are straightforward.\u00a0 Each pin (a<\/em> through g<\/em>) of the seven segments LED are connected to the digital I\/O of the Netduino through a resistor and from our code we are controlling which to turn high or low. The seven segments LED used in this tutorial is a common cathode and there are four units of them combined into one whose internal connection looks like this.<\/p>\n

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Four units Common Cathode Seven Segments LED<\/p><\/div>\n

In order to turn the LED on, we need to set the anode pins to high and selected cathode to ground. Question is, how can we ground the selected pin when we need? If we can connect a switch and then toggle the switch when need to ground will work for us. To facilitate this, we can use transistor as a switch<\/strong>. Connecting transistor as a switch is what we already have learned in first tutorial (Basic Input and Output<\/a>). As shown in the circuit, we have connected the base of each transistor to certain Digital I\/O of our Netduino, emitter is grounded and collector is connected to anodes of seven segments LED. When the base of transistor is set to high, transistor\u2019s switch turns on then the corresponding anode gets connected to ground which completes the circuit and turns the LED to ON.<\/p>\n

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Circuit Digram connecting Seven Segments LED and LDR<\/p><\/div>\n

Connection with Netduino or Netduino Plus<\/h2>\n
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Breadboard Connection: Seven Segments LED and Netduino <\/p><\/div>\n

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

This time our code looks little intensive as I have created little library (SevenSegments<\/em> Class) that supports little more than displaying digits. Let\u2019s look at it step by step. In the code below, we first created an instance of AnalogInput <\/em>class which allows us getting the value from our analog device which is LDR in this case. Then we created a separate instance of SevenSegments<\/em> class. The constructor of this class takes several pins as arguments. Once we have SevenSetments<\/em> instance we simply call the Show method and pass the value that we read from Analog device.<\/p>\n\n

public<\/span> static<\/span> void<\/span> Main(<\/span>)<\/span>\n{<\/span>\n \n    AnalogInput aInPin =<\/span> new<\/span> AnalogInput(<\/span>Pins.<\/span>GPIO_PIN_A1<\/span>)<\/span>;<\/span>  \/\/use any analog pin<\/span>\n    aInPin.<\/span>SetRange<\/span>(<\/span>0<\/span>, 1234<\/span>)<\/span>;<\/span> \/\/give a range.<\/span>\n \n    Debug.<\/span>Print<\/span>(<\/span>"Analog value: "<\/span> +<\/span> aInPin.<\/span>Read<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\n \n    \/\/ initialize the seven segments LED and pass appropriate pins<\/span>\n    SevenSegments sevenSegments =<\/span> new<\/span> SevenSegments(<\/span>\n        Pins.<\/span>GPIO_PIN_D0<\/span>, Pins.<\/span>GPIO_PIN_D1<\/span>, Pins.<\/span>GPIO_PIN_D2<\/span>,\n        Pins.<\/span>GPIO_PIN_D3<\/span>, Pins.<\/span>GPIO_PIN_D4<\/span>, Pins.<\/span>GPIO_PIN_D5<\/span>, Pins.<\/span>GPIO_PIN_D6<\/span>,\n        new<\/span> Cpu.<\/span>Pin<\/span>[<\/span>]<\/span> {<\/span> Pins.<\/span>GPIO_PIN_D8<\/span>, Pins.<\/span>GPIO_PIN_D9<\/span>, Pins.<\/span>GPIO_PIN_D10<\/span>, Pins.<\/span>GPIO_PIN_D11<\/span> }<\/span>)<\/span>;<\/span>\n \n    \/\/ Display value read by analog device<\/span>\n    sevenSegments.<\/span>FlickerDelay<\/span> =<\/span> 5<\/span>;<\/span> \/\/ Pause between each letter during repetition in a LED unit<\/span>\n    sevenSegments.<\/span>UnitSevenSegmentLedDelay<\/span> =<\/span> 1<\/span>;<\/span> \/\/Duration of a LED unit being ON<\/span>\n    sevenSegments.<\/span>UnitRepetition<\/span> =<\/span> 50<\/span>;<\/span> \/\/ Repetition of entire strip<\/span>\n    while<\/span> (<\/span>true<\/span>)<\/span>\n    {<\/span>\n        sevenSegments.<\/span>Show<\/span>(<\/span>aInPin.<\/span>Read<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\n        Debug.<\/span>Print<\/span>(<\/span>aInPin.<\/span>Read<\/span>(<\/span>)<\/span>.<\/span>ToString<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\n    }<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
 <\/p>\n
Main heavy lifting is done in the SevenSegment<\/em> class. So, let\u2019s take a quick look at different sections of this class.<\/p>\n
Constructor section of the SevenSegment Class<\/h3>\n
Here we have defined some Digital I\/O for LED segments\u00a0a<\/em> through g<\/em>. To support any number of LED units, the common Anode or Cathode pins are received as an array. Now, to show a letter or an alphabet, I have constructed an array of Boolean<\/em>. All such arrays are stored in a HashTable<\/em> with a key<\/em> that corresponds to a digit or an alphabet or a symbol. Finally a few properties are initialized with some values.<\/p>\n\n
public<\/span> SevenSegments(<\/span>Cpu.<\/span>Pin<\/span> a, Cpu.<\/span>Pin<\/span> b, Cpu.<\/span>Pin<\/span> c, Cpu.<\/span>Pin<\/span> d, Cpu.<\/span>Pin<\/span> e, Cpu.<\/span>Pin<\/span> f,\n                                 Cpu.<\/span>Pin<\/span> g, Cpu.<\/span>Pin<\/span>[<\/span>]<\/span> commonAnodeCathodePin)<\/span>\n{<\/span>\n\u00a0 \u00a0 \/\/ (wire color is for personal reference)<\/span>\n\u00a0 \u00a0 OutputPort PinD0Out_a =<\/span> new<\/span> OutputPort(<\/span>a, false<\/span>)<\/span>;<\/span> \/\/11 \u00a0Black\u00a0<\/span>\n\u00a0 \u00a0 OutputPort PinD1Out_b =<\/span> new<\/span> OutputPort(<\/span>b, false<\/span>)<\/span>;<\/span> \/\/7 \u00a0 Brown<\/span>\n\u00a0 \u00a0 OutputPort PinD2Out_c =<\/span> new<\/span> OutputPort(<\/span>c, false<\/span>)<\/span>;<\/span> \/\/4 \u00a0 Red<\/span>\n\u00a0 \u00a0 OutputPort PinD3Out_d =<\/span> new<\/span> OutputPort(<\/span>d, false<\/span>)<\/span>;<\/span> \/\/2 \u00a0 orange<\/span>\n\u00a0 \u00a0 OutputPort PinD4Out_e =<\/span> new<\/span> OutputPort(<\/span>e, false<\/span>)<\/span>;<\/span> \/\/1 \u00a0 Yellow<\/span>\n\u00a0 \u00a0 OutputPort PinD5Out_f =<\/span> new<\/span> OutputPort(<\/span>f, false<\/span>)<\/span>;<\/span> \/\/10 \u00a0Green<\/span>\n\u00a0 \u00a0 OutputPort PinD6Out_g =<\/span> new<\/span> OutputPort(<\/span>g, false<\/span>)<\/span>;<\/span> \/\/5 \u00a0 Blue<\/span>\n \n\u00a0 \u00a0 segmentPins =<\/span> new<\/span> OutputPort[<\/span>]<\/span> {<\/span> PinD0Out_a, PinD1Out_b, PinD2Out_c, PinD3Out_d,\n                                                PinD4Out_e, PinD5Out_f, PinD6Out_g }<\/span>;<\/span>\n \n\u00a0 \u00a0 \/\/ initialize commonAnodeCathodePin<\/span>\n\u00a0 \u00a0 ledSegmentUnit =<\/span> new<\/span> OutputPort[<\/span>commonAnodeCathodePin.<\/span>Length<\/span>]<\/span>;<\/span>\n\u00a0 \u00a0 for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i &<\/span>lt;<\/span> commonAnodeCathodePin.<\/span>Length<\/span>;<\/span> i++<\/span>)<\/span>\n\u00a0 \u00a0 {<\/span>\n\u00a0 \u00a0 \u00a0 \u00a0 ledSegmentUnit[<\/span>i]<\/span> =<\/span> new<\/span> OutputPort(<\/span>commonAnodeCathodePin[<\/span>i]<\/span>, false<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 }<\/span>\n \n\u00a0 \u00a0 \/\/ create a list of supported display<\/span>\n\u00a0 \u00a0 ledSegmentTable =<\/span> new<\/span> Hashtable(<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"0"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"1"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, false<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"2"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"3"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"4"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"5"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"6"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"7"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, false<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"8"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"9"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"a"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"b"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"c"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"d"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"e"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"f"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"g"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span> ;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"h"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"i"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, false<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"j"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"l"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"n"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, true<\/span>, false<\/span>, true<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"o"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"p"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"q"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"r"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, false<\/span>, false<\/span>, true<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"s"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"t"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"u"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, true<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"y"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"-"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, false<\/span>, false<\/span>, false<\/span>, false<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"?"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> false<\/span>, true<\/span>, true<\/span>, false<\/span>, true<\/span>, true<\/span>, false<\/span> }<\/span>)<\/span>;<\/span>\n\u00a0 \u00a0 ledSegmentTable.<\/span>Add<\/span>(<\/span>"?"<\/span>, new<\/span> bool<\/span>[<\/span>]<\/span> {<\/span> true<\/span>, false<\/span>, false<\/span>, true<\/span>, false<\/span>, false<\/span>, true<\/span> }<\/span>)<\/span>;<\/span>\n \n\u00a0 \u00a0 \/\/ Initialize fields to its default<\/span>\n\u00a0 \u00a0 FlickerDelay =<\/span> 5<\/span>;<\/span>\n\u00a0 \u00a0 SevenSegmentsUnits =<\/span> commonAnodeCathodePin.<\/span>Length<\/span>;<\/span>\n\u00a0 \u00a0 UnitSevenSegmentLedDelay =<\/span> 0<\/span>;<\/span>\n\u00a0 \u00a0 UnitRepetition =<\/span> 50<\/span>;<\/span>\n\u00a0 \u00a0 RightToLeft =<\/span> true<\/span>;<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Public Show Methods<\/h3>\n
To show a digit or alphabet, we have exposed a Show<\/em> method in the class. There are three overloads of this Show<\/em> method. First one takes int<\/em> as an argument and directly calls second Show<\/em> method which takes string<\/em> as an argument. In this method, depending on whether RightToLeft<\/em> is set to true<\/em> or false<\/em>, code jumps to corresponding section. This section basically extracts the right letter to display and then calls the third Show method.<\/p>\n\n
public<\/span> void<\/span> Show(<\/span>string<\/span> stringToShow)<\/span>\n{<\/span>\n \n    \/\/ this loop will make it appear that all the LED units remained ON.<\/span>\n    for<\/span> (<\/span>int<\/span> j =<\/span> 0<\/span>;<\/span> j &<\/span>lt;<\/span> UnitRepetition;<\/span> j++<\/span>)<\/span>\n    {<\/span>\n \n        if<\/span> (<\/span>RightToLeft)<\/span>\n        {<\/span>\n            int<\/span> ledUnit =<\/span> SevenSegmentsUnits -<\/span> 1<\/span>;<\/span> \/\/ 0 based index<\/span>\n \n            for<\/span> (<\/span>int<\/span> i =<\/span> stringToShow.<\/span>Length<\/span>;<\/span> i &<\/span>gt;<\/span> 0<\/span>;<\/span> i--<\/span>)<\/span>\n            {<\/span>\n                string<\/span> eachLetter =<\/span> stringToShow.<\/span>Substring<\/span>(<\/span>i -<\/span> 1<\/span>, 1<\/span>)<\/span>;<\/span>\n                Show(<\/span>eachLetter, ledUnit)<\/span>;<\/span>\n                ledUnit -=<\/span> 1<\/span>;<\/span>\n \n                \/\/ If length of  stringToShow is greater than SevenSegmentsUnits rest it<\/span>\n                if<\/span> (<\/span>ledUnit &<\/span>lt;<\/span> 0<\/span>)<\/span> ledUnit =<\/span> SevenSegmentsUnits -<\/span> 1<\/span>;<\/span> \/\/ - 1 as it's 0 based index<\/span>\n \n                Thread.<\/span>Sleep<\/span>(<\/span>UnitSevenSegmentLedDelay)<\/span>;<\/span>\n            }<\/span>\n        }<\/span>\n        else<\/span>\n        {<\/span>\n            int<\/span> ledUnit =<\/span> 0<\/span>;<\/span> \/\/ 0 based index<\/span>\n            for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i &<\/span>lt;<\/span> stringToShow.<\/span>Length<\/span>;<\/span> i++<\/span>)<\/span>\n            {<\/span>\n                string<\/span> eachLetter =<\/span> stringToShow.<\/span>Substring<\/span>(<\/span>i, 1<\/span>)<\/span>;<\/span>\n                Show(<\/span>eachLetter, ledUnit)<\/span>;<\/span>\n                ledUnit +=<\/span> 1<\/span>;<\/span>\n \n                \/\/ If length of  stringToShow is greater than SevenSegmentsUnits rest it<\/span>\n                ledUnit =<\/span> ledUnit %<\/span> SevenSegmentsUnits;<\/span>\n \n                Thread.<\/span>Sleep<\/span>(<\/span>UnitSevenSegmentLedDelay)<\/span>;<\/span>\n            }<\/span>\n        }<\/span>\n \n        Thread.<\/span>Sleep<\/span>(<\/span>FlickerDelay)<\/span>;<\/span>\n    }<\/span>\n \n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
The third Show method takes two arguments, first one is the string to display and second one is where to display i.e. in which LED unit to display. From the HashTable<\/em> defined during construction, it finds out the correct array of Boolean<\/em> then corresponding pin is set to high or low based on this Boolean<\/em> array. In final step, all common anode or cathode pins are set to low then only the appropriate LED unit is set to high.<\/p>\n\n
public<\/span> void<\/span> Show(<\/span>string<\/span> numberString, int<\/span> ledUnit)<\/span>\n{<\/span>\n    bool<\/span>[<\/span>]<\/span> ledSegmentOnOffValues;<\/span>\n    numberString =<\/span> numberString.<\/span>ToLower<\/span>(<\/span>)<\/span>;<\/span>\n \n    \/\/ at this level, string of unit lenght is supported so drop the rest<\/span>\n    if<\/span> (<\/span>numberString.<\/span>Length<\/span> &<\/span>gt;<\/span> 1<\/span>)<\/span> numberString =<\/span>\n             numberString.<\/span>Substring<\/span>(<\/span>numberString.<\/span>Length<\/span> -<\/span> 1<\/span>, 1<\/span>)<\/span>;<\/span>\n \n    \/\/ Send Low to the common anode\/cathode of SevelSegmentLED<\/span>\n    for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i &<\/span>lt;<\/span> ledSegmentUnit.<\/span>Length<\/span>;<\/span> i++<\/span>)<\/span>\n    {<\/span>\n        ledSegmentUnit[<\/span>i]<\/span>.<\/span>Write<\/span>(<\/span>false<\/span>)<\/span>;<\/span>\n    }<\/span>\n \n    if<\/span> (<\/span>!<\/span>ledSegmentTable.<\/span>Contains<\/span>(<\/span>numberString)<\/span>)<\/span>\n    {<\/span>\n        \/\/ when non supported letter is passed display "-"<\/span>\n        ledSegmentOnOffValues =<\/span> (<\/span>bool<\/span>[<\/span>]<\/span>)<\/span>ledSegmentTable[<\/span>"-"<\/span>]<\/span>;<\/span>\n    }<\/span>\n    else<\/span>\n    {<\/span>\n        \/\/ get the true\/false array<\/span>\n        ledSegmentOnOffValues =<\/span> (<\/span>bool<\/span>[<\/span>]<\/span>)<\/span>ledSegmentTable[<\/span>numberString]<\/span>;<\/span>\n    }<\/span>\n \n    for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i &<\/span>lt;<\/span> segmentPins.<\/span>Length<\/span>;<\/span> i++<\/span>)<\/span>\n    {<\/span>\n        \/\/make the corresponding pin high<\/span>\n        segmentPins[<\/span>i]<\/span>.<\/span>Write<\/span>(<\/span>ledSegmentOnOffValues[<\/span>i]<\/span>)<\/span>;<\/span>\n    }<\/span>\n \n    \/\/ Only send signal to the selected Anode\/Cathode<\/span>\n    ledSegmentUnit[<\/span>ledUnit]<\/span>.<\/span>Write<\/span>(<\/span>true<\/span>)<\/span>;<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Expansion of\u00a0 SevenSegments Class with a Counter<\/h3>\n
With a very few lines of code we can expand or add additional functionality such a counter which counts from min to max value. This Counter is a very simple example that takes two arguments, min value and the max value. A for<\/em> loop has been setup from this min to max value and the Show method has been called passing the current loop increment. This method enables us to display the counter in our seven segments LED unit.<\/p>\n\n
public<\/span> void<\/span> Counter(<\/span>int<\/span> minValue, int<\/span> maxValue)<\/span>\n{<\/span>\n    for<\/span> (<\/span>int<\/span> i =<\/span> minValue;<\/span> i &<\/span>lt;=<\/span> maxValue;<\/span> i++<\/span>)<\/span>\n    {<\/span>\n        Show(<\/span>i)<\/span>;<\/span>\n        Debug.<\/span>Print<\/span>(<\/span>i.<\/span>ToString<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\n    }<\/span>\n}<\/span><\/pre><\/td><\/tr><\/table><\/div>\n\n
Output<\/h2>\n
With our SevenSegments class, we have several outputs. First let\u2019s look at the output of our circuit. Here we can see the lower value in our display when LDR is covered however the number goes up as we illuminate our LDR.<\/p>\n
 <\/p>\n
\"\"<\/a>
Seven Segments LED displaying letter 'L'<\/p><\/div>\n
 <\/p>\n