LCD display and clock

Many LED or LCD displays consist of seven segments. By turning these segments on in different ways, we can display the digits from 0 to 9:

 ###         ###   ###         ###   ###   ###   ###   ### 
#   #     #     #     # #   # #     #         # #   # #   #
#   #     #     #     # #   # #     #         # #   # #   #
#   #     #     #     # #   # #     #         # #   # #   #
             ###   ###   ###   ###   ###         ###   ### 
#   #     # #         #     #     # #   #     # #   #     #
#   #     # #         #     #     # #   #     # #   #     #
#   #     # #         #     #     # #   #     # #   #     #
 ###         ###   ###         ###   ###         ###   ### 

In this project we want to implement a clock that displays the time in LCD-format.

We will build up the project in small steps, one function at a time.

lcdDigit

Let us number the seven segments from 0 to 6 as follows:

  555  
 4   0 
 4   0 
 4   0 
  666  
 3   1 
 3   1 
 3   1 
  222  

I have made a table which tells us which segment to turn on for each digit:

val digits = 
  listOf(listOf(true, true, true, true, true, true, false),     // 0
	listOf(true, true, false, false, false, false, false),  // 1
	listOf(true, false, true, true, false, true, true),     // 2
	listOf(true, true, true, false, false, true, true),     // 3
	listOf(true, true, false, false, true, false, true),    // 4
	listOf(false, true, true, false, true, true, true),     // 5
	listOf(false, true, true, true, true, true, true),      // 6
	listOf(true, true, false, false, false, true, false),   // 7
	listOf(true, true, true, true, true, true, true),       // 8
	listOf(true, true, true, false, true, true, true),      // 9
	listOf(false, false, false, false, false, false, false)) // Blank

For example, digits(5) is a list of 7 Boolean's, telling us to switch on segments 1, 2, 4, 5, 6. Note the entry with index 10, which simply displays a blank.

Your first task is to write a function

fun lcdDigit(digit: Char, k: Int, c: Char): String {
  // ...
}

This function takes a character digit and returns a string that represents this character in LCD-format. k is the size of the LCD-display, c is the character to be used for the LCD-display.

When digit is not a digit, the function should simply return a blank string. You can use the following code to convert digit to an index for the digits table:

  val d = if ('0' <= digit && digit <= '9') digit - '0' else 10

Here are some examples for the output:

$ ktc
Welcome to Kotlin version 1.0.1-2 (JRE 1.7.0_101-b00)
Type :help for help, :quit for quit
>>> :load lcd1.kts
>>> lcdDigit('0', 2, '*')
 ** 
*  *
*  *
    
*  *
*  *
 ** 
>>> lcdDigit('4', 3, '&')
     
&   &
&   &
&   &
 &&& 
    &
    &
    &
     
>>> lcdDigit('9', 5, 'M')
 MMMMM 
M     M
M     M
M     M
M     M
M     M
 MMMMM 
      M
      M
      M
      M
      M
 MMMMM 
>>> lcdDigit('a', 3, 'M')
     
     
     
     
     
     
     
     
     

Note that the character 'a' is simply displayed as a blank.

Note that the function does not print the digit itself. It only returns a string. Since this string goes over several lines, it needs to contain the "new-line" character, which you can enter as \n. There should be no new-line character at the beginning and at the end of the output string.

Combine

Next we need a function that combines two digits:

fun combine(left: String, sep: String, right: String): String {
  // ...
}

This function needs to split both left and right into pieces at the new-line characters. It then adds the pieces together, and finally generates a new string.

You can use s.split("\n") to split a string into a list of strings, and r.joinToString(separator = "\n") to compose a list of strings into a single long string.

Here are some examples:

>>> combine("This\nis\nfun", "&", "Hello\nCS109\nStudents!")
This&Hello
is&CS109
fun&Students!
>>> combine(lcdDigit('0', 3, '*'), " # ", lcdDigit('9', 3, '@'))
 ***  #  @@@ 
*   * # @   @
*   * # @   @
*   * # @   @
      #  @@@ 
*   * #     @
*   * #     @
*   * #     @
 ***  #  @@@ 

lcd

Next, we need a function that takes a string and changes it to LCD-format. To save you some typing, here it is:

fun lcd(s: String, k: Int, c: Char, sep: String): String {
  var result = lcdDigit(s[0], k, c)
  for (i in 1 until s.length)
    result = combine(result, sep, lcdDigit(s[i], k, c))
  return result
}

Test the function and check that it works well:

 
>>> lcd("12:45:99", 4, '@', ":")
      : @@@@ :      :      : @@@@ :      : @@@@ : @@@@ 
     @:     @:      :@    @:@     :      :@    @:@    @
     @:     @:      :@    @:@     :      :@    @:@    @
     @:     @:      :@    @:@     :      :@    @:@    @
     @:     @:      :@    @:@     :      :@    @:@    @
      : @@@@ :      : @@@@ : @@@@ :      : @@@@ : @@@@ 
     @:@     :      :     @:     @:      :     @:     @
     @:@     :      :     @:     @:      :     @:     @
     @:@     :      :     @:     @:      :     @:     @
     @:@     :      :     @:     @:      :     @:     @
      : @@@@ :      :      : @@@@ :      : @@@@ : @@@@ 

A real clock

If you got the lcd-function working, there is nothing to stop us from implementing our clock. Since it's mostly special functions for obtaining and formatting the current time, I wrote it for you:

fun clearScreen() {
  println("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n")
}

fun clock() {
  val form = java.text.SimpleDateFormat("HH mm ss")
  var current = form.format(java.util.Calendar.getInstance().getTime())
  clearScreen()
  println(lcd(current, 4, '#', " "))
  while (true) {
    Thread.sleep(100)
    val ntime = form.format(java.util.Calendar.getInstance().getTime())
    if (ntime != current) {
      current = ntime
      clearScreen()
      println(lcd(current, 4, '#', " "))
    }
  }
}

Note that it runs forever. You can stop it by typing Ctrl+C.