Your assignment is to design a voting machine that is immune to tampering because it's not programmable. It should offer the voter a choice of two candidates and record the votes using two 5-bit binary counters. Polling is to be private but supervised by a human operator. The machine should be designed to run like this:
1) The supervisor pushes a button (call it "READY") to enable the machine to record the next vote.
2) The voter chooses a candidate by pushing one of two buttons ("candA" or "candB"). An LED associated with each button indicates the selection. The voter can change the selection any number of times. The vote will not be recorded until the next step.
3) The voter pushes a third button ("CAST") to cast the vote. The machine should not accept any changes after this, nor allow multiple votes by the same voter.
4) The supervisor again pushes the READY button, enabling the machine for the next voter. Pushing the button also should clear the LED indicators so that the next voter does not see the choice just recorded.
In this procedure "pushing a button" means pressing and releasing it. The buttons are "momentary switches" - that is, they give a logic "1" when pressed and logic "0" when released. So, for example, when the supervisor pushes the button to enable the machine for another voter, the READY signal toggles from 0 to 1 then back to 0.
You can assume that an LED indicator can be attached to any signal or logic gate output and will light up if the signal or gate is at logic "1".
To summarize, your machine should have four logic inputs (READY, CAST, candA, candB), two LEDs to indicate which of the two candidates has been selected, and two binary counters producing the output, which is the count for each candidate.
This can be done using combinatorial logic gates (AND, OR, NAND, NOR, NOT, and so on) and sequential logic (SR latches, D-flip flops, T-flip flops). You won't need all of these things. My solution involved about a dozen logic components, not including the counters.