How to design a synchronous counter 4 bit using JK flip flop that can count up even numbers from 0 to 14, and count down odd numbers from 15 to 0 in 1 system - Quora
60 Second Timer
Counter (digital) - Wikipedia
Synchronous 4-Bit counter circuit using JK-flip-flops | TikZ example
Counter with 4 flip flops jk synchronous from 3 to 13! - Electrical Engineering Stack Exchange