Depending upon how the coin sensors and output of the machine are implemented, you might need some more states to allow for the fact that a coin might be hitting a switch for an arbitrary length of time; I don't see anything in your machine to handle that.  It's also not clear how long the "dispense product" output is supposed to be active.  A logical possibility would be that "dispense product" should remain active until a signal is returned from the mechanism indicating that the product has been dispensed, whereupon the machine should reset to its start state.

Also, if you are going to use RS latches, you need to design your machine so that if multiple latches switch simultaneously for a state transition, it won't matter whether one switches before the other.  If the machine was sitting in state "01" and a nickel arrived, it would attempt to transition into state "10".  If Q0 and Q1 are RS latches, there is no reason to expect them to switch simultaneously.

If you want to minimize the number of states, the theoretical minimum set, assuming the dispensing mechanism's cycle will last at least as long as a coin input would be:


Nothing inserted
Switches active with $0.05
Switches idle with $0.05
Switches active with $0.10
Switches idle with $0.10
Total of $0.15 inserted (switch state irrelevant)


Six states, probably allowing a three-bit state machine.  I would conjecture, though, that you might find it easier to use different states for the "switch active with second nickel" and "switch active with first dime" scenarios.  Also, you might be able to reduce circuitry further if you use four latches in two pairs, where the states of the first pair of latches are computed using the outputs of the second, and the second pair of latches copies the state of the first whenever no coins are present.

New to circuits, confused about where reset happens with SR flip-flop
How do I have a link within a word document to certain text strings of the file name?

For example, I am editing a word document where the file name is: 'File 075 - Test result 101.doc', and would like to only use the strings 'File 075' rather than the full file name in the word document as a automatic link / field that updates itself when the file name changes.

How would you proceed with it?
