Counters - Synchronous, Asynchronous, up, down & Johnson ring counters
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
4 Bit Ripple Counter – Electronics Hub
Counters - STUDYTRONICS
4 bits Synchronous Counter with J K Flip Flop - YouSpice
4 bit Asynchronous Counter with J K Flip Flop - YouSpice
Design steps of 4-bit asynchronous up counter using J-K flip-flop