# 4 bit Binary Adder to Dual 7 segment decoder 0-15

#### Marvin Abrigo Peralta

Joined Mar 16, 2018
3
So we are task on creating a circuit that will add 0-15 in binary and will produce an output to a dual 7 segment(connected to a decoder 7447), my problem right now is that I can only produce up to 19 in decimal and once I try to produce a sum of 20 it doesn't show up, and I still need to make up to sum of 30( 1111 + 1111), how can we implement this, How can we decode this? What combination circuits do I need to add ?

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#### WBahn

Joined Mar 31, 2012
28,468
Don't just give a schematic (that is known not to work) and expect others to have to figure out how you intended it to work before they can even start figuring out why it isn't doing what you wanted it to to.

Describe your approach to solving the problem. How did you break it down? Then describe how you solved the individual pieces. Then describe how your implemented the solution to each part and how it is supposed to work. Then describe how you brought these pieces together to solve the overall problem.

Don't be surprised if that, in doing this, you discover what your doing wrong and how to fix it.

#### dl324

Joined Mar 30, 2015
15,535

Why would you expect the circuit to be able to display a number larger than 19 when you don't use the D2/4/8 inputs for the MSD decoder?

Post the complete text of the problem so we can understand what you're trying to accomplish.

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#### Marvin Abrigo Peralta

Joined Mar 16, 2018
3
I'm beginning from scratch, so the problem is to add from 0-15 using 74LS83 and will produce an output from 0-30 and will display the sum to a dual 7 segment. From what I know the decoder 74LS47 can only display from 0-9 in a 7 segment unless a combinational circuit is implemented. Example is 1101(13) + 1010(10) = 10111(23), how can the decoder show this kind of output to the 7 segment display?

#### WBahn

Joined Mar 31, 2012
28,468
The first step in solving a problem is to clearly state the problem and then break it down into small, manageable tasks.

You aren't trying add from 0-15. You are trying add two 4-bit binary numbers. You are then trying to display the sum as a two-digit decimal value on a dual 7-segment display.

So what are the steps involved in doing this? Think of the stages you would go through if you were doing it by hand.

#### Marvin Abrigo Peralta

Joined Mar 16, 2018
3
Truth Table > KMap right?

#### WBahn

Joined Mar 31, 2012
28,468
Truth Table > KMap right?
You aren't ready for truth tables and k-maps until you can clearly layout the tasks that need to be solved in sufficiently fine detail to make a meaningful truth table.