Electronic circuit : 24 Second Shot Clock

A new 24 second countdown timer from Milardo. The circuits uses fast 74LS schottky IC's.

Notes
Here is how the circuit works:
A 24 second countdown starts when S3 is off and S2 is pressed.

Switch S3 is used to start/pause the countdown. S2 resets the countdown (99 to 00) when the countdown reach 00.

To restart the countdown to 24 Seconds S1 is pressed.