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8 bit adder

Discussion in 'Electronics Homework Help' started by Alpha500, Jan 5, 2011.

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  1. Alpha500

    Alpha500

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    Jan 5, 2011
    I need to make a binary adder ( not actually sure if this is 8 bits or 16 bits)
    There will be 2 8-bit inputs (each one represents 2 digits in binary)
    The output will be 8 LED's displaying the sum (again in binary)
    There will be limitations, but this is what I need to do.
    The only thing i can find is 4 bit full adders. I am not sure how to connect them or how many I need.

    01010100 01101000 01100001 01101110 01101011 00100000 01011001 01101111 01110101 00100001
     
    Last edited: Jan 5, 2011
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    To add 2 8 bit numbers you use an 8 bit adder. You will need 9 leds to show the result.

    Have a look at the datasheets for the 4 bit adders, they should show how to combine them for more bits.

    59 6f 75 27 72 65 20 57 65 6c 63 6f 6d 65
     
  3. Alpha500

    Alpha500

    6
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    Jan 5, 2011
    thank you again :D
    I'm not exactly sure, what is the 9th LED for?
    it will be like this
    42 on the output would be 0100 0010
    the space is just a gap in the LEDs
    also, i heard that there was a 7-seg display that has 4 binary inputs.
    i don't know if these are sold, but if so where can i get some?

    EDIT
    I found out how to do it (i think)
    you connect the carry out from one adder into the carry in of the second.
    this is for the very first thing we are doing in electronics. most people are making some combonation gates (like 3 way and/or) and I am making an adder :D
     
    Last edited: Jan 5, 2011
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,299
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    Jan 21, 2010
    The ninth LED? What is the sum of 1000 0000 and 1000 0000?

    You seem to have the right idea. This indicates how it's done at a lower level, which makes it (or should make it) much clearer.

    A 7 segment display that had 4 inputs would be one that includes a BCD to 7-seg converter/driver. But unless you also want to convert binary to BCD you'd be looking for one that handles a - f in addition to 0 - 9. I'm not sure that any such combined thing exists, do you'd be looking at the converter/driver and a display.

    Are you planning to make an adder from gates, or will you be using an adder chip? In fairness to you, I'm not sure that the latter is appropriate for your first "thing". I'd be building it from discrete gates, and perhaps contenting myself with far fewer bits.
     
  5. Alpha500

    Alpha500

    6
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    Jan 5, 2011
    *refers to binary chart*
    80+80...
    oh. i see what you mean.
    so the ninth LED will light if there is a carry over from second chip?
    the max without the carry over light would be 99, now it is 199
    i think my adder is done (microwave dings)

    116 104 97 110 107 32 121 111 117 32 40 97 103 97 105 110 41

    the assignment really was to "build an electric circuit"
    this qualifies as an electric circuit =)
    of course, you couldn't have just taped some wires to a battery and an LED.
     
    Last edited: Jan 5, 2011
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Fair enough.

    OK, but how are you (planning on) driving the LEDs?

    And what logic family and power supply are you (planning on) using?
     
  7. Alpha500

    Alpha500

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    Jan 5, 2011
    when the output of the adders goes back to the power supply , there will be an LED in each of the outputs before the outputs connect.
    logic family... not sure what this even is
    the power supply will be DC around 5 volts
     
    Last edited: Jan 5, 2011
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,299
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    Jan 21, 2010
    OK, if you're going to overachieve, please do it properly ;)

    first the family. Are the chips 74Cxx, 40xx, 74LSxx, or something else? Are you using all the same type? Do you know the power supply requirements for them? Are you taking anti-static precautions (if the logic family requires it).

    AND does the logic family have outputs capable of driving LEDs, and do you need a series resistor?

    Out of interest... how are you building this? on a breadboard?
     
  9. Alpha500

    Alpha500

    6
    0
    Jan 5, 2011
    logic family: HC or CMOS
    supply voltage: 5V
    grounded

    the supply voltage will overload the LEDs, and if i add a resistor it will not be enough for the counters to function.
    EDIT: got it now. put the resistors and LEDs in parralel?

    and yes, I am using a breadboard.
     
    Last edited: Jan 6, 2011
  10. Alpha500

    Alpha500

    6
    0
    Jan 5, 2011
    I tried to use windows paint to make a schematic, but I cant upload it.
    I think I know what to do now. I'm going to put it into an electronic simulator, and hope it works.
     
    Last edited: Jan 6, 2011
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