[11/10] Logisim - 4-bits Count-down w/ 4x J-K Flip Flops

For my Computer Organisation module, I implemented a 4-bits count-down circuit using four J-K Flip Flops. The counter counts down from 1010 (10 in decimal) to 0000 (0 in decimal).

The steps took were:

1. Find out for each current state, what the wanted next state is

2. For each of the states and the variables (bits, ABCD's) find the appropriate J and K values 

3. For each of the J, K values for each variable (bits - so that would be 8 in total), draw a Karnaugh map and find the min. SOP expression

4. Using the SOP expressions, implement the circuit - make sure the Q outputs head back to the LED's of the appropriate variable (bit)

5. Use the clock to count down

While I was building the circuit through Logisim, I realised that a JK Flip-Flop makes it convenient to handle multiple variables that are changing, because it has the 'toggle' command. For instance, if the current state is (0,0), you can either toggle it (J=1, K=1) or set J=1, K=0 to make the zeros change to one. Constructing my Karnaugh maps, I realised that this leads to simpler SOP expressions for each J's and K's, which led to a rather simple circuit as below!