Help Designing Digital Elevator Simulation

[sndp_2002]

I need some help designing a Digital elevator simulation using multi media logics. I need some help and guidelines as to how I should get the thruth diagrams, kmaps and the circuit going.

I am required to design a digital circuit which has applications in elevator style controls. My circuit will ne able to accept 4 momentary closed switches (push buttons) as input, for selecting one of four levels (i.e. 0, 1, 2 & 3). The output of the circuit will be the value of the presently selected level on a seven (7) segment LCD display. Additionally, my circuit should light one of four (4) LEDs corresponding to the push button which is activated. The circuit must maintain the state of all outputs even after a push button is released; only changing state when another button is activated. The circuit should be robust enough to cater for the possibility of several buttons being simultaneously activated by only registering the highest level of those selected.

Please help me

 

[berkeman]

First, you will need to debounce the switches. Do you know how to do that? Then you will need to synchronize these switch inputs with a system clock. Have you learned how to do that yet? Are you supposed to have any real-time delay in this circuit to emulate the time it takes for the elevator to move between floors, or are you supposed to just make the movement instantaneous?

You should draw a state diagram that shows how the outputs change according to the previous state and the inputs. Have you learned about Mealy and Moore state machines yet and how to design them? Quiz question -- what's the difference between those two types of state machines?

 

[sndp_2002]

I am suppose to design the circuit and then simulate it in the multimedia logic software.. I have not covered the areas you mentioned above. I don't know where and how to begin

Thank you for responding

 

[berkeman]

It's hard to believe that they have given you that assignment without any classroom or textbook instruction to enable you to tackle the design. What have you been learning in that class and related classes so far?

Here's a note from wikipedia.org about asynchronous systems like your elevator controller (asynchronous because the buttons can be pushed at any time with respect to the system clock):

from http://en.wikipedia.org/wiki/Digital_circuit

In comparison, asynchronous systems are [challenging] to design because all possible states, in all possible timings must be considered. The usual method is to construct a table of the minimum and maximum time that each such state can exist, and then adjust the circuit to minimize the number of such states, and force the circuit to periodically wait for all of its parts to enter a compatible state. (This is called "self-resynchronization.") Without such careful design, it is easy to accidentally produce asynchronous logic that is "unstable", that is, real electronics will have unpredictable results because of the cumulative delays caused by small variations in the values of the electronic components. Certain circuits (such as the synchronizer flip-flops, switch debouncers, and the like which allow external unsynchronized signals to enter synchronous logic circuits) are inherently asynchronous in their design and must be analyzed as such.

Here is some info on state machines from wikipedia -- you should understand the basics of state machines first, and then apply that to the design of your elevator controller:

http://en.wikipedia.org/wiki/State_machine

You should also go to your technical library and check out "The Art of Electronics" by Horowitz and Hill. Switch debouncing is covered in section 8.16 and synchronizer circuits are covered in section 8.19 (those section numbers are from my 1st edition copy -- the latest edition may have slightly different numbering).

 

[berkeman]

BTW, I should clarify one thing. The interface to the buttons is the asynchronous part of your design. Once the buttons are debounced and those signals synchronized to the system clock, the state machine that you will design is synchronous.

 

[sndp_2002]

the tip we received from the lecturer is priority encoder for the first stage then use a flip flop then led drivers these will help us design the circuit

so far we have covered binary, k maps, truth table, basic gates, flip flop, and decoders the rest we have to research

I cannot relate what we have covered so far to this design
If i get a clear picture in my head i will be able to do it