7-segment display 3-to-8 decoder logic circuit (please help, thank you)

Thread Starter


Joined Nov 16, 2015
Hello everyone,

I am required to create a logic circuit that uses a 7-segment display with a 3-to-8 decoder to show the number 1 5 6 6 9 5 5 7 sequentially on a single display.

Some notes:
  • You are NOT required to simplify equations - rather, you're required to use a 3-to-8 decoder to simplify/reduce the number of logic gates.

  • You only need to submit the circuit built with the decoder.
Attached is a Word file containing my Truth Tables and derived Boolean Expressions. I'm really hoping somebody might be able to take a quick look at these to make sure I've been doing them correctly. Also included is what I hope/believe to be the start of my circuit containing the 3-to-8 decoder...is it correct?

It is at this point that I am totally stuck. I have ready many tutorials but just can't seem to grasp how this works. I can not derive the circuit from my equations, I simply find it too difficult. Could anyone please show me one or two sections showing how my equations translate into the circuit and then how that circuit fits into the larger circuit as a whole. The decoder has really thrown me off.

I hope that I have provided you with enough material to show you that I've really been trying very hard to understand this task. It has taken a lot of work with my very basic knowledge to even get to this point! For the last two days I've been trying to understand the processes on my own but now I feel I really do need help. If you need any further information then please ask.

Thanks so much for your time and any help you can provide.



Joined Apr 11, 2010
Just as a heads-up, many people will not open a stranger's word doc, as it is a vector for a virus/malware attack. Can you post the information directly?

If you do not know or are unsure how to post images, take a look at this blog.


Joined Mar 31, 2012
I'm still not following what the requirements are.

As best I can guess, you get to use one 3-to-8 decoder and one 7-segment display along with some basic gates for glue logic between them. Then the sequential display is accomplished by walking the inputs of the decoder through the eight possible states sequentially. Is that about right?

Is this a common-anode or a common-cathode display?

Let's focus on just one of the segments, say segment 'e'. You want this to be on exactly when the input to the decoder is either ABC = 010 or 011. What does that translate to in terms of the outputs?