# Designing a calculator with specific functions

#### Teslathunder

Joined Apr 4, 2021
4

there is a typo error at point 3, ''0-7'' not ''0-6''. I do not know how to achieve point 5 and 7. PLs help ME, thank you very much...

#### Ya’akov

Joined Jan 27, 2019
8,505
What have to built so far? What have you tried that doesn't work?

#### click_here

Joined Sep 22, 2020
548
To me that would mean that the second input gets deleted.

ie
1+2
whoops, I meant 6
*delete*
1+
1+6
*enter*

And the answer should be visible in either octal or decimal format

#### Teslathunder

Joined Apr 4, 2021
4
To me that would mean that the second input gets deleted.

ie
1+2
whoops, I meant 6
*delete*
1+
1+6
*enter*

And the answer should be visible in either octal or decimal format
Yes, i do not how to design the circuit that achieve these functions

#### Teslathunder

Joined Apr 4, 2021
4
What have to built so far? What have you tried that doesn't work?
I had done all points (except point 5 and point 7), which is the on/off switch, clear push buttons, octal numbers 0-7 push buttons, adding the octal numbers together (encoder>registers>adders>decimal adder), display them on 7-segment displays, and also doing the design using the universal gate, NAND gate only.

#### Ya’akov

Joined Jan 27, 2019
8,505
Schematic? Photos?

#### click_here

Joined Sep 22, 2020
548
I'm guessing that you have some sort of keypad, maybe you could use the clear button - short press delete, long press clear

And maybe pressing the enter button for a 2nd time after the answer is being displayed changes it to Dec - Make sure that you have an LED or something to say if dec/oct is being displayed

#### Teslathunder

Joined Apr 4, 2021
4

#### BobaMosfet

Joined Jul 1, 2009
2,102

#### DickCappels

Joined Aug 21, 2008
10,104
Your schematic does not label the parts nor their function - it is more like the wiring diagram for a washing machine or refrigerator. Can you produce a schematic that shows that the design involves (what kinds of chips are these, and what are their functions?

#### click_here

Joined Sep 22, 2020
548
Is this homework?
I guess it is because it's in the "homework help" section.

#### DickCappels

Joined Aug 21, 2008
10,104
An attempt to take the discussion out of Homework Help has been removed,and further attempts can result in restrictions on the perpetrator's membership privledges. We are here to help the student learn, not do the work for them.

#### MrAl

Joined Jun 17, 2014
10,898
View attachment 234442
there is a typo error at point 3, ''0-7'' not ''0-6''. I do not know how to achieve point 5 and 7. PLs help ME, thank you very much...
Wow octal, havent seen that since the 1980's. In the 1970's we had to program some chips in octal but everything pretty much went to hex after that.

To build anything with pure logic (as it sounds like you have to do) you should write up some expressions that lead to your solution. A large part of it comes from 'selector' type logic where a certain input creates a certain binary output, or a certain binary input creates a certain single output. For example, a "1 of 8 decoder". You can then figure out how to design the decoder itself.
But also of interest is what you have done in the past, or what you were instructed to do because you probably are being asked a question that builds on that previous work.

I actually built several calculators in the past.
My first was from a single chip that did all the math and the output appeared on an LED display with digits just 0.2 inches high. IT only did addition, subtraction, multiplication, and division.
Another was programmed into a ROM using a Z80 CPU.
Since then most of my calculators (including ones that can solve differential equations) have been on the PC computer using either C or a derivative or another language.
Today however if i had to design a hardware calculator i would definitely start with a microcontroller. There are good algorithms out there for sin and cos and stuff like that, and addition and subtraction are quite simple and multiplication and division are just a derivative of those two (in the absence of a numerical chip that is).

Using pure logic though like with NAND gates can be quite a challenge because there is a lot of logic that has to go into it. Do you really have to use discrete logic like that?
If so since you have to work in both decimal (base 10) and octal (base 8) the first thing i think i would do is design a decimal to octal converter and/or octal to decimal converter. That in itself is a challenge but then again i dont know how many digits you have to use for the design. If ti is just one digit you got it made, two digits a little harder, more just adds more logic chips.

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