4 bit Asynchronous Counter with J K Flip Flop - YouSpice
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
Design steps of 4-bit (MOD-16) synchronous up counter using J-K flip-flop
Binary 4-bit Synchronous Up Counter
Virtual Labs
NJIT - COE 394 Digital Systems Laboratory - Experiment No.7: Counters
Ripple Counter - Circuit Diagram, Timing Diagram, and Applications