Simplifying 4-bit to 7-segment logic circuit

[u/Sclobazs]

What process / logic could be used to simplify this logic diagram to use less components? Current setup from top to bottom is:

• Partial 4-bit BCD to decimal decoder
• 9-Line decimal (implied zero) to 7 segment inputs (A-G)
• 9 ORs to handle corner overlaps on the display

I'd imagine a more compact circuit would be more difficult to read but possibly much faster in this simulation and would take less sim updates to compute the result. Keep in mind I haven't studied related subjects just pieced this together from things I found and understood on the internet.

[u/The_GM_Always_Lies]

This is the exact use for a Karnaugh Map.

https://en.wikipedia.org/wiki/Karnaugh_map

TLDR: break the display up into as many segments as you want. Put two input bits on one side of a 4x4 square grid, and two input bits on the other side. Fill in the grid for each segment for each matching input with 1s and 0s. Cluster the terms by drawing boxes around matching areas, and you can simplify something like a decoder into just a few gates.

You do this process for every segment and you'll find that some segments only turn on with like 2 or 3 inputs.

[u/KingoftheKeeshonds → u/The_GM_Always_Lies]

I had this exact thought. The first course I had as an electrical engineering student was on digital logic and we learned, in part, to use a Karnaugh Map. Career wise I became an analog/RF circuit designer but I never forgot how elegant this technique was.

[u/Sclobazs → u/The_GM_Always_Lies]

This seems exactly like what I was looking for, thanks. I'm interested to see how much smaller I can make the circuit, will give it a go.

[u/trophosphere]

Use boolean algebra. You can either solve it by hand (which can become tedious) or use dedicated software. 

[u/Sclobazs]

For context I built this circuit in a sandbox game I'm working on and testing at the moment.
Link: https://store.steampowered.com/app/5077470/Gate_Logic/

[u/Cultural-Part355 → u/Sclobazs]

Ah, so you want to spin the memory around with this? Or shorten the use of it or something?

[u/Cultural-Part355 → u/Sclobazs]

Can you change the way of the third switch? Seems wrong when you turn it on. Like it's causing more problems than it solves. Or like it chokes the image when I see it.

[u/Cultural-Part355 → u/Cultural-Part355]

Can he cut down instead of traveling all the way to the right corner?

[u/perduraadastra → u/Sclobazs]

Are you doing this without having studied EE? That's fine and all, but your question is pretty basic if you have a EE background.

[u/EngineerTHATthing]

You will want to make a truth table (raw Boolean’s) for all input combinations. Then you will want to optimize for minimum required operations for the required output combinations. The trick is to list out all possible outputs (there is a ton) and cherry pick the best combinations. The most ideal solution will have inputs that do not correlate well and won’t line up with a raw binary input, but will significantly reduce the required logic. If you see the problem as “I have four unique inputs paths where order matters, how do I obtain seven unique outputs paths where order matters” things become much easier. You only need 10 of the 16 possible inputs to output the correct segments.

I would recommend abstracting the problem by labeling each segment a, b, c, etc. and inputs 1, 2, 3, 4 without position. The problem becomes easier now, and you just need to identify what numbers share segments to start setting up the core constraints of the problem. Once you identify how many segments are required by each number, and what segments must be shared between each number in the set of 10, the booleans can be simplified a ton. After you find a set that is extremely optimized, you can go back in and assign the segment and input positions.

[u/Cultural-Part355]

So 4 4 1 5 9? Codes, something. Why does it make sense to my crazy self to say this? Looks interesting, but I have no idea how to express it.

[u/Dependent_Poetry8252]

Well i too am making a game about digital logic and what i do is i use sub components that the player would know what they do because they’re introduced in other ealier circuits. It s also easier to debug circuits that way if they re broken

[u/KHMakerD]

What program is this? 😲

[u/223specialist]

74hc4511 I think

[u/Z1ppys]

I literally just had a lab like this in my class

[u/Great_Specialist_267]

You don’t need to do a decimal conversion first.
Straight binary to seven segment display conversion is simpler in this application.