Flip Flop JK Down Counter Display (Test) | Tinkercad
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
Synchronzähler – Wikipedia
How to implement a 3 bit odd counter with JK flip flops - Quora