This is an impulse generator, which creates every 2 min, 5 min, 10 min or 25 min an impulse of one second (displayed on LED5). The delay between the pulses is selected with the buttons S1 to S4 and displayed with LED1-4: Every 1/15625s the buttons are sampled and the next 124/15625s the GPIOs are set to output to display the selected delay with the LEDs.
A layout could look like this:
Rendered with Eagle3D :
