digital design

Hi, I have 17 LED strips, and a 20A, 5V PSU. It has 3 terminals for COM, and 3 for V+. I have run 4 sets of automotive power cable, so my strips are powered by different cable runs. 3 of the cables power 4 LED strips, and 1 powers 5, for a total of 17 LED strips. For simplicity, my diagram...

I want to construct a circuit that calculates the absolute value of a signed 4-bit number in two's complement! So the logic here : assuming we have B = b3 b2 b1 b0 . If b3 is '1' then then b is already in 2s complemnt and should be assigned directly to the output else if b3 is equal to '0' then...

I need to design an Automated system such that a user gives inputs in 3 bits and there's a clock running that resets itself and gives a positive signal after the time indicated by input. We can use logic gates, combinatorial circuits, sequential circuits, counters, registers.

So i'm having trouble on a Digital Design assignment. I'm supposed to create a circuit in logisim that checks whether a BCD number is a palindrome or not. This is easy enough when the length of the number is given but apparently I'm supposed to do this without knowing the length of the number...