On Thu, Jul 11, 2013 at 1:57 PM, S. Dale Morrey <[email protected]> wrote:
> My birthday is coming up in a month and my wife asked me what I want.
> I decided I want to go really bare metal and build my own pocket calculator.
> I found this kit...
> http://www.spikenzielabs.com/Catalog/index.php?main_page=product_info&products_id=762
>
> The only problem I see is that it's using a programmable microcontroller.
> That sort of feels like cheating. I'd prefer to build one from discrete
> logic units, even if the result would be big, bulky and slow. I just want
> to geek out and learn something in the process.
>
> Does anyone know of a calculator kit or project using discrete logic?
>
> Thanks!
If you are doing this as a circuit assembly/soldering exercise, it
doesn't matter whether your ICs contain discrete logic elements or
little microcontrollers. If you are doing it to learn something about
how a calculator works, isn't it also cheating to get a kit that tells
you how to wire discrete logic elements into a calculator?
What you need is an introductory digital logic book or web page, a
variety of logic ICs in DIP format, a keypad, a 7-segment display, a
good-sized breadboard, some wire, and miscellaneous
resistors/capacitors/etc. required to safely hook them all together.
All of which are likely to be found at any number of electronic
hobbyist stores.
Now, learn to build an adder from NAND gates. Learn how to combine
adders to implement the basic arithmetic operations. Learn how to
build a flip-flop from NAND gates, and how to build a memory register
from flip-flops. Learn how to combine them all into a basic
calculator.
After you have the logic figured out, you need to learn the messy
analog bits that are still required to debounce buttons and power
digital circuits. Fortunately these are pretty simple as far as
analog circuits go.
Now you plug all your components into the breadboard, hook them up
correctly with jumper wires, and scratch your head and replace
burnt-out components as you try to figure out what you did wrong.
Finally, once you get it all working, you can lay out a circuit board
and etch it and solder all your components on and go through a couple
more head-scratching iterations until you have a working calculator!
Or, you could just buy the kit and have a cool gadget sitting on your
desk. How much time do you want to devote to this? :)
--Levi
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