Connect with us

Help with Logic Circuit

Discussion in 'Electronic Basics' started by John, Jul 30, 2005.

Scroll to continue with content
  1. John

    John Guest

    I am a new to this group but

    Can anyone help I need to make a logic circuit
    that lights a single LED when a BCD counter
    is at specific numbers and not at any others

    I need the LED to light when the BCD below is
    at 1, 3 , 6 , 8 and at no other time

    any help please

    D C B A
    0 - 0 0 0 0
    1 - 0 0 0 1
    2 - 0 0 1 0
    3 - 0 0 1 1
    4 - 0 1 0 0
    5 - 0 1 0 1
    6 - 0 1 1 0
    7 - 0 1 1 1
    8 - 1 0 0 0
    9 - 1 0 0 1


    T.I.A

    John G
     
  2. Dan Hollands

    Dan Hollands Guest

    use 4 four input AND ( gates to decode the four conditions and then a four
    input OR gate to provide an output when any of the conditions are met.

    Actual implementation will probably use NAND or NOR gates

    --

    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
    585-872-2606

    www.QuickScoreRace.com
     
  3. Dan Hollands

    Dan Hollands Guest

    use 4 four input AND ( gates to decode the four conditions and then a four
    input OR gate to provide an output when any of the conditions are met.

    Actual implementation will probably use NAND or NOR gates

    --

    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
    585-872-2606

    www.QuickScoreRace.com
     
  4. Lord Garth

    Lord Garth Guest

    Look in alt.binaries.schematics.electronic for a schematic of one possible
    circuit.
     
  5. vic

    vic Guest

    The logic function you need to wire is
    A*!B*!C*!D + A*B*!C*!D + !A*B*C*!D + !A*D

    This can be simplified and factorized (karnaugh might help).
    After this you can deduce the needed circuit using the logic gates you
    choose.

    vic
     
  6. vic

    vic Guest

    The logic function you need to wire is
    A*!B*!C*!D + A*B*!C*!D + !A*B*C*!D + !A*D

    This can be simplified and factorized (karnaugh might help).
    After this you can deduce the needed circuit using the logic gates you
    choose.

    vic
     
  7. John Fields

    John Fields Guest

    ---

    D>--+--------+
    | |
    +--[INV]-|---------+---------+---------+
    | | | |
    C>--+--------|---------|-+ | |
    | | | | | |
    +--[INV]-|-+-------|-+-------|-+-------|-+
    | | | | | | | |
    B>--+--------|-|-------|-|-+-----|-|-+ | |
    | | | | | | | | | | |
    +--[INV]-|-|-+-----|-|-|-----|-|-|-----|-|-+
    | | | | | | | | | | | |
    A>--+--------|-|-|-----|-|-|-----|-|-|-+---|-|-|-+
    | | | | | | | | | | | | | | |
    +--[INV]-|-|-|-+---|-|-|-+ | | | | | | | |
    | | | | | | | | | | | | | | | |
    | | | | | | | | | | | | | | | |
    | _ _ _ _ | | _ | | _ _ _ _ _ |
    D C B A D C B A D C B A D C B A
    AND AND AND AND
    Y Y Y Y
    | | | |
    | +---+ +---+ |
    +-----------+ | | +-----------+
    | | | |
    D C B A
    OR
    Y
    |
    |
    [LED]
    |
    [R]
    |
    GND
     
  8. Bob Eldred

    Bob Eldred Guest

    If it were me, I'd make a one chip solution using an 8 pin DIP PIC processor
    with an internal clock an no other parts except a resistor and the LED. The
    code is trivial and simply subtracts (compares) the four bit input with the
    four possible bit patterns in a continuous repeating sequence. When a hit is
    made, the subtraction equals zero and the resulting zero status bit is used
    to set the output port true lighting the LED. This conditionis is latched
    true and remains that way through each sequence. If there is no hit or all
    hits are removed, the resulting non zero status clears the latch and the LED
    goes off.
     
  9. John

    John Guest

    Thanks for all your help guys

    This as got to be the friendliest group I have been on



    To let you know how I got round my problem



    I used a 4028 BCD to Decimal decoder linking the

    Decimal outputs of 1 , 3 , 6 , 8 together with diodes

    The same as Lord Garths circuit to feed the LED



    Once again everyone thanks for all your help







    John G
     
  10. John Fields

    John Fields Guest

    ---
    Assuming that the OP has specified that what's supposed to happen to
    the LED in between valid hits is that it's supposed to go dark, the
    solution _is_ trivial and was posted earlier by, I think, Lord
    Garth. No disrespect intended, since sometimes the road to the
    trivial solution is long and winding.
     
  11. Well mylord,

    Nice solution but you can do even slightly better :) See below.

    +-----------------+
    | __ | __
    A--+-+-| | +-| |
    | |& |o--+ +------|& |o--+
    +-|__| | | +----|__| |
    __ | | | |
    C----+-| | | | | |
    | |& |o----+ | __ | __
    +-|__| +--------| | +---| |
    +-----------------|& |o------|& |o- A*/C*/D
    B----------------------|__| +---|__| +/A*B*C
    __ | | | + /A*D
    D----+-| | | | |
    | |& |o------+ __ |
    +-|__| +--------| | |
    | |& |o--+
    +-----------------|__|
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    One 00 (quad 2 input NAND) and one 10 (triple 3 input NAND). Like you, I
    suppose the values 1010-1111 don't care or don't happen.

    Personally I'd go for a small PIC or tiny AVR solution but you need some
    skills and equipment to program them which the OP may not has available.

    petrus bitbyter
     
  12. Well mylord,

    Nice solution but you can do even slightly better :) See below.

    +-----------------+
    | __ | __
    A--+-+-| | +-| |
    | |& |o--+ +------|& |o--+
    +-|__| | | +----|__| |
    __ | | | |
    C----+-| | | | | |
    | |& |o----+ | __ | __
    +-|__| +--------| | +---| |
    +-----------------|& |o------|& |o- A*/C*/D
    B----------------------|__| +---|__| +/A*B*C
    __ | | | + /A*D
    D----+-| | | | |
    | |& |o------+ __ |
    +-|__| +--------| | |
    | |& |o--+
    +-----------------|__|
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    One 00 (quad 2 input NAND) and one 10 (triple 3 input NAND). Like you, I
    suppose the values 1010-1111 don't care or don't happen.

    Personally I'd go for a small PIC or tiny AVR solution but you need some
    skills and equipment to program them which the OP may not has available.

    petrus bitbyter
     
  13. Well mylord,

    Nice solution but you can do even slightly better :) See below.

    +-----------------+
    | __ | __
    A--+-+-| | +-| |
    | |& |o--+ +------|& |o--+
    +-|__| | | +----|__| |
    __ | | | |
    C----+-| | | | | |
    | |& |o----+ | __ | __
    +-|__| +--------| | +---| |
    +-----------------|& |o------|& |o- A*/C*/D
    B----------------------|__| +---|__| +/A*B*C
    __ | | | + /A*D
    D----+-| | | | |
    | |& |o------+ __ |
    +-|__| +--------| | |
    | |& |o--+
    +-----------------|__|
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    One 00 (quad 2 input NAND) and one 10 (triple 3 input NAND). Like you, I
    suppose the values 1010-1111 don't care or don't happen.

    Personally I'd go for a small PIC or tiny AVR solution but you need some
    skills and equipment to program them which the OP may not has available.

    petrus bitbyter
     
  14. Lord Garth

    Lord Garth Guest


    Hey, I like your solution too Petrus! Yes, A-F is not supposed to occur as
    it is fed
    from a BCD counter. The OP used a 1of 10 decoder though I preferred to go
    after it
    with low level logic. That was a tiny bit of fun and a trip down memory
    lane!
     
  15. Rich Grise

    Rich Grise Guest

    You use a 74HC42:
    http://www.semiconductors.philips.com/pip/74HC42.html

    And you just pick the outputs you need. If you need
    to light the _same_ LED for any of the four, just
    connect four diodes, cathodes to the chip pins, and all
    four anodes to the LED cathode, and adjust your
    resistor for the other diode drop.

    Cheers!
    Rich
     
  16. Lord Garth

    Lord Garth Guest


    You must have missed his reply Rich, he used a CMOS 1 of 10 demux
    and wire OR'd the outputs.
     
  17. Rich Grise

    Rich Grise Guest

    Yeah, it wsa about 4 posts down-thread. =:-O

    Sorry. ;-)
    Rich
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-