// 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
              ;
             
             

              }