Wanted a clock that was agile enough to be able to handle different start time splits, 30 seconds, 1 and 2 minutes.  Shows 10 seconds to go, then count down from 5 seconds to a GO signal with a start tone.  Display the rider number and name of the next rider.  

Another function is a countdown timer for 90 minutes or less and keeps track of the number of times the lap button is pressed, using an opto isolated switch and a GPIO pin.  This calculates the average lap time of a Criterium bicycle race.  Once the time is less than 1/2 of the total time, the clock transitions to the number of laps to complete the race based on the calculated average lap time.  

Displayed on a 132 x 32 led matrix using a Raspberry Pi and C and C++ as the code.  I made the wood case surrounding the clock, which features a matte black surround on the led matrix side to reduce reflections, LCD touch screen for easy interaction with Pi.