# Displaying multiple outputs on the same seven segment with a time difference of two seconds

Discussion in 'Homework Help' started by Deena_94, Dec 24, 2014.

1. ### Deena_94 Thread Starter New Member

Dec 24, 2014
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0
Hello everyone,
I'm working on this voting machine system. First of all, here's the description:
Four candidates (A, B, C, D) are contesting an election. The voting machine consists of four push buttons. There are 100 voters, and we will assume that the maximum number of votes any candidate gets is 99 (to save on our 7-segment units more than anything else). To display the number of votes, we want to follow somewhat devious means, again to save on 7-segment units. In this scheme, there are four LED’s (A, B, C, D).There are two 7-segment display units to indicate numbers from 0 to 99 in the good old decimal notation. After each vote, we will spend 8 seconds to look at the latest results. In the first two seconds, LED A lights, and the score displayed is that for candidate A. This is followed by B, C, D, and we are ready for the next voter. Provide a Master Enable switch.

Now, I have made four 0-99 counters using 7490 chips. My problem is how I am to display the results successively on the same pair of seven segments. I've been thinking maybe I should use a 555 timer with a shift register (I'm not very familiar with shift registers either and I can't find anything online) to enable each of my 7447 decoders in order, but I realized there's no enable pin in the 7447 decoders. So any ideas how I should do the 2 seconds thingee for my seven segment display?

Thank you very much in advance.

2. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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3,961
Ahhhhh!

Why would you do such a thing with discrete logic? Fine, it might be a good learning exercise, but it has *no* application in today's CPU/MPU driven world.

A microcontroller begs to be used in an application like this and will be far more flexible. Why don't you give it a try?

3. ### Deena_94 Thread Starter New Member

Dec 24, 2014
3
0

Sadly, I'm not allowed to use micro-controllers. It's a college thing.

4. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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3,961
Fine. You only need 1 7447 for each LED numeral.

You'll need to multiplex the output of each of your counters to the 7447s. A separate counter would iterate through each of the vote accumulator counters.

That's as much help as you'll get out of me. I haven't done discrete logic in 25 years.

Deena_94 likes this.
5. ### Deena_94 Thread Starter New Member

Dec 24, 2014
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Thanks a lot, monsieur. I appreciate your help. Multiplexers are highly considered now.

6. ### WBahn Moderator

Mar 31, 2012
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This should really be in Homework Help -- you'd probably get more feedback there as the folks that like to help students learn tend to concentrate there and many spend the bulk of there time there.

The next step is to make a state diagram that walks through the states that you have (how many states DO you have?) and then determine what makes the system go from one state to another and what has to happen in each state.