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This is the simulation of my counter circuit. It works as reversable synchronous counter with these states: 0, 3, 6, 1, 4, 7 (shown in binary). It contains only three J-K flip-flops and the rest is 12 NAND gates of combination logic.

The hardware version is finished and working but I don't have any photos yet, only video. It consist of two double J-K flip-flops (74HC112, the fourth works with button as clock enable), three quad 2-input NAND gates (74AC00, 4011, 4093), one hex inverter (4049, can be also one more 4x2 NAND; two gates with resistor and capacitor make oscillator for clocking the J-K flip-flops), two buttons (clock enable and direction), CR2032 lithium cell, three LEDs and some resistors and capacitors. All these fit on one row breadboard :)