// By Kyle McDonald
                  
                  

                   // From the instructables project at:
                  
                  

                   // http://www.instructables.com/id/DIY-3D-Controller/
                  
                  

                   

                  
                  

                   #define resolution 8
                  
                  

                   #define mains 50 
                   // 60: north america, japan; 50: most other places
                  
                  

                   

                  
                  

                   #define refresh 2 * 1000000 / mains
                  
                  

                   

                  
                  

                   void 
                   setup
                   () 
                   {
                  
                  

                     
                   Serial
                   .
                   begin
                   (
                   115200
                   );
                  
                  

                   

                  
                  

                     
                   // unused pins are fairly insignificant,
                  
                  

                     
                   // but pulled low to reduce unknown variables
                  
                  

                     
                   for
                   (
                   int 
                   i 
                   = 
                   2
                   ; 
                   i 
                   < 
                   14
                   ; 
                   i
                   ++
                   ) 
                   {
                  
                  

                       
                   pinMode
                   (
                   i
                   , 
                   OUTPUT
                   );
                  
                  

                       
                   digitalWrite
                   (
                   i
                   , 
                   LOW
                   );
                  
                  

                     
                   }
                  
                  

                   

                  
                  

                     
                   for
                   (
                   int 
                   i 
                   = 
                   8
                   ; 
                   i 
                   < 
                   11
                   ; 
                   i
                   ++
                   )
                  
                  

                       
                   pinMode
                   (
                   i
                   , 
                   INPUT
                   );
                  
                  

                   

                  
                  

                     
                   startTimer
                   ();
                  
                  

                   }
                  
                  

                   

                  
                  

                   void 
                   loop
                   () 
                   { 
                  
                  

                     
                   Serial
                   .
                   print
                   (
                   time
                   (
                   8
                   , 
                   B00000001
                   ), 
                   DEC
                   );
                  
                  

                     
                   Serial
                   .
                   print
                   (
                   " "
                   );
                  
                  

                     
                   Serial
                   .
                   print
                   (
                   time
                   (
                   9
                   , 
                   B00000010
                   ), 
                   DEC
                   );
                  
                  

                     
                   Serial
                   .
                   print
                   (
                   " "
                   );
                  
                  

                     
                   Serial
                   .
                   println
                   (
                   time
                   (
                   10
                   , 
                   B00000100
                   ), 
                   DEC
                   );
                  
                  

                   

                  
                  

                   } 
                  
                  

                   

                  
                  

                   long 
                   time
                   (
                   int 
                   pin
                   , 
                   byte 
                   mask
                   ) 
                   {
                  
                  

                     
                   unsigned 
                   long 
                   count 
                   = 
                   0
                   , 
                   total 
                   = 
                   0
                   ;
                  
                  

                     
                   while
                   (
                   checkTimer
                   () 
                   < 
                   refresh
                   ) 
                   {
                  
                  

                       
                   // pinMode is about 6 times slower than assigning
                  
                  

                       
                   // DDRB directly, but that pause is important
                  
                  

                       
                   pinMode
                   (
                   pin
                   , 
                   OUTPUT
                   );
                  
                  

                       
                   PORTB 
                   = 
                   0
                   ;
                  
                  

                       
                   pinMode
                   (
                   pin
                   , 
                   INPUT
                   );
                  
                  

                       
                   while
                   ((
                   PINB 
                   & 
                   mask
                   ) 
                   == 
                   0
                   )
                  
                  

                         
                   count
                   ++
                   ;
                  
                  

                       
                   total
                   ++
                   ;
                  
                  

                     
                   }
                  
                  

                     
                   startTimer
                   ();
                  
                  

                     
                   return 
                   (
                   count 
                   << 
                   resolution
                   ) 
                   / 
                   total
                   ;
                  
                  

                   }
                  
                  

                   

                  
                  

                   extern 
                   volatile 
                   unsigned 
                   long 
                   timer0_overflow_count
                   ;
                  
                  

                   

                  
                  

                   void 
                   startTimer
                   () 
                   {
                  
                  

                     
                   timer0_overflow_count 
                   = 
                   0
                   ;
                  
                  

                     
                   TCNT0 
                   = 
                   0
                   ;
                  
                  

                   }
                  
                  

                   

                  
                  

                   unsigned 
                   long 
                   checkTimer
                   () 
                   {
                  
                  

                     
                   return 
                   ((
                   timer0_overflow_count 
                   << 
                   8
                   ) 
                   + 
                   TCNT0
                   ) 
                   << 
                   2
                   ;
                  
                  

                   }