I want to make a timer that counts down from 15 minutes, in 5 minute intervals.
It should use 3 LEDs, and behavious should be such that when it is switched on, all 3 LEDs are lit. Then after 5 mins one of the LEDs goes out. Then after another 5 mins another LED goes out, and finally after 5 more minutes the final LED goes out.
This is my first stab at circuit design, so I wondered if someone could give this the once over. I suspect I've missed some key components, so any corrections or advice would be much appreciated.
Here's the circuit, based on a 4060B to do the timing, and a 4017 decade chip to keep count. There's also a 4049 inverter to ensure the LEDs go off as the pins go high, and a 74AC11032 chip to facilitate the "or" logic.