GVSU Pinewood Derby

1
GVSU Pinewood Derby

• EGR 450
• Greg Cooke
• Bob Humphrey

2
Goals

• Modify pinewood derby track for addition of new
  components.
• Create timing system for 4-lane pinewood derby to
  display time from start to finish for each car,
  using Motorola 68HC11.
• Write software in assembly language for control
  of 68HC11 and implementation of timing system.

3
Track Modification

• Contact added on start lever completes circuit
  when race started, setting a bit on the 68HC11.
• Plexiglass arms added at finish line with metal
  contacts under track to complete a circuit.
• Cars knock arms over, break contact, clearing a
  bit on the 68HC11.

4
And Theyre Off!

• When start lever completes circuit, software
  detects and branches to a race subroutine.
• Inside race subroutine, the current value of
  68HC11s free-running timer is stored in memory
  for later calculations.
• Race subroutine then repeatedly checks bits to
  see when cars finish, until all cars have
  finished.

5
The Race

• The 68HC11s free-running timer has a range of
  524.3ms. The timer will overflow several times
  during the race.
• Accumulator B is used as an overflow counter.

6
Finish Line

• Cars knock arms over, breaking a circuit,
  clearing a bit in memory.
• As each car finishes, software detects the bit
  change and stores the current timer value and
  current overflow count in memory locations
  designated for each cars data.

7
Post-Race Calculation

• The start timer value will be the same for each
  car. That value is subtracted from the timer
  range and stored.
• For each car, the timer range is multiplied by
  the overflow count and stored.
• Also for each car, the start timer value is added
  to the overflow time and the finish time, giving
  a total time.
• The total time is then stored in memory.

8
And the Winner Is

• The times for each lane are displayed down to the
  hundredth of a second in Hyperterminal.
• Times are always displayed from lane 1 to lane 4.
  
• The results remain on the screen until a start
  button is pressed, indicating that a new race is
  ready to begin.