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Building a claculator with existing parts...

Discussion in 'Electronic Basics' started by [email protected], Jan 11, 2006.

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  1. Guest

    Hi everyone!

    I want to start by saying that I am new to this hobby but I have always
    been interested in the idea of creating my own little devices... My
    background is mostly in computer science and not much of electronics...
    The reason I decided to get into this field is to design and build a
    device that I had in mind for some time now... but it's way too
    complicate for me at this stage so I decided to start with building a

    My calculator will consist of:
    a number pad
    a display
    and a small thermal printer... (to print the results or whatever)

    I got all of those parts from different places... (old electronics)

    The reason I decided to build a calculator is because by doing this I
    will learn a lot of relevant material to building my device.

    Now my guess is that this calculator will have to have some kind of a
    CPU to control all of those components and some kind of memory (to
    store numbers). I am not looking to design and create everything from
    scratch.... so I would not be making the CPU and the memory, I just
    want to properly implement those components.

    That is as far as I get... I need some advice on what kind of
    CPU/memory would be best... and a pointer to some tutorials or reading
    material that will help me with this project. Also any tips or advice
    is appreciated.

  2. Puckdropper

    Puckdropper Guest

    wrote in
    You may want to take a look at such things as adders or subtractors. You
    can do the four basic mathematical operations (add, subtract, multiply,
    divide) with just addition. (What is subtraction? Adding a negative.
    Division? Adding a negative a certain number of times.)


    Old computers are getting to be a lost art. Here at Uncreative Labs, we
    still enjoy using the old computers. Sometimes we want to see how far a
    particular system can go, other times we use a stock system to remind
    ourselves of what we once had.

    To email me directly, send a message to puckdropper (at)
  3. Guest

    Since you're a computer guy and are willing to put in a microcontroller
    to run the hardware anyway, why not just do the calculator in the
    controller? Scanning keys is not difficult and interfacing to an LCD
    display also easy. You'll definitely have some fun with binary
    arithmetic (assuming you try fractions or floating point). The software
    to convert your binary answers to ASCII for the display is also a good

    Personally I like Freescale but lots of folks here use PICs, Atmels and
    others so help is available.

    Sounds like a fun project -- just don't expect it to be a TI or HP.

  4. Jasen Betts

    Jasen Betts Guest

    easiest way is to use a microcontroller, if you proogram it in C there may
    be a math (arithmetic really) library that can do most of the hard work,
    but you can program it in assembler and implement the operations yourself
    if you want to learn about that sort of thing.
    calculators don't need a large amouunt of ram, or wide registers,
    as little as 32 bytes could be anough, but I see you've got a number
    of devices to interface with so a micro with plenty of pins could
    be a good idea.

  5. Geir_HK

    Geir_HK Guest

    Gess you're wrong about the _divide_ function. I beleive that you need
    something more than only adders. It's easy on paper for integers, but
    doing that with a board filled with 47xx must be almost imposible.

    So, How would you build a circuit that can divide an 8 bit integer in
    another 8 bit integer-value?
  6. First, I suspect that Puckdropper may have meant that programming code
    would do the division operation and that it was possible to do so with
    repeated subtraction, which isn't quite the best but can be made to

    But taking your question as to direct circuitry instead of software
    running on a processor with only addition and subtraction/negation, it
    can be done either with sequential or combinatorial logic or
    combinations of that and for signed or unsigned. It's all doable and
    I can lay out a simple divider either way for you here, if you doubt
    it. The combinatorial case is a pain, usually creating quite a chain
    of add/compares and muxes and makes the sequential methods look so
    much better than similar comparisons for multipliers. But it's doable
    and not unreasonably. Sequential methods are pretty stock and easily

  7. Sjouke Burry

    Sjouke Burry Guest

    No, divide is subtract/shift/repeat, I had to do that
    in an ARM riscprocessor which had only add/subtr/mulitply.
    You use the same method (in base 10 instead of base 2) when
    you do it by hand.
  8. Jasen Betts

    Jasen Betts Guest

    it's like multiplying by shifting and adding
    except you compare and subtract instead of adding ...

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