help with a 4 bit full adder using four 3×8 decoders

Discussion in 'The Projects Forum' started by RadwaU, Sep 4, 2011.

  1. RadwaU

    Thread Starter New Member

    Sep 4, 2011
    Hi everyone,,

    two months ago we were assigned with this beautiful project ^^
    anyway we spent plenty of time and money on it but it didn't work,,
    we have tried almost everything,,

    the project was a 4 bit full adder using four 3×8 decoders and displaying the output on 2 seven segments display,,

    the input is in binary (we used switches for it),, so the max number that should appear on the 7-seg.s' is 30

    we made the truth table of course,,
    here it is

    now the problem was to convert the five binary output (S1-S4, C1) from the gates into BCD so that we can use it with the two BCD to 7 segment decoders,,

    we bought this chip for it,,
    it's suppose to convert the 5 binary outputs (S1, S2, S3, S4, C1) from the decoders into BCD,,

    TDA4092 Datasheet,,

    but still it didn't work,,

    we tried something else,,

    that is to convert binary to BCD using gates,, we did it with the truth table of course,,

    here is the Truth Table

    the plan was as follows:
    we want the output (M0 - M7) from the input (S1-S4 , C1)
    so we got each (M) using (AND & OR gates),,
    for example,,

    M2 is active high form 20 to 30,,
    so M2 = (S3*C1) + (S1*S3*C1) +(S2*S3*C1) +.... etc

    here is the schematic,,


    it's too large,, and is very complicated,, 5 people including the our Teacher Assistant have checked this over 20 times,, so it is 99.9% correct,, :D

    so?? where the hell is the problem :confused::confused::confused:
  2. bertus


    Apr 5, 2008

    The post was made invisible by the forum software.
    Perhaps there are some issues with the site you use to show us the pictures.
    We prefer to have the pictures uploaded to our server, so they will be preserved better, as external sites may "disappear" at once.

    Sorry for the inconvenience.

  3. vrainom


    Sep 8, 2011
    Hey look again at that TDA4092 datasheet, at the very beggining it says: "5 bit binary to 7 segment decoder driver" so its output is not BCD but direct 7 segments display data
  4. RadwaU

    Thread Starter New Member

    Sep 4, 2011
    ok here are the pictures,,
  5. RadwaU

    Thread Starter New Member

    Sep 4, 2011

    oh am sorry that was my mistake,, we did that actually but still,, didn't work @@

    I was more wondering about the mistake of the other solution??!

    is it a wrong idea??
    Last edited: Sep 13, 2011