keypad and 7 segment

Discussion in 'The Projects Forum' started by abuarab88, Mar 24, 2009.

  1. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    hello all,

    we want to design a circuit using akeypad and two 7 segment such that
    when we enter for example17 the 7 segment shows 17 and 99
    7 segment gives 99

    now how can i build this circuit and what should i put between the keypad and the 7 segment

    and thank you all
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    You should put a microcontroller between the keypad and the display.
    You will benefit greatly from the process of learning to program a microcontroller. PIC and AVR controllers seem to be very popular for this sort of thing.
     
  3. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Go for the PIC.. without uC its a pain in your head even for such simple things.. You will also have new experiences..
     
  4. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    i hope it was that easy,
    but you see
    our prof asked us not to use pic
    we must use the original ways
    using the combinational gates
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    So this needs to be done with NAND/NOR gates, or 74xxx series logic?

    Overview:
    Scan keypad one column at a time, read row output, when a row + column is high, key is pressed. Map key to number to display on first digit. Continue scanning until another key is pressed, map key to number to display on second digit. Reset display on next keypress and display first digit again.

    Shift registers, latches, and some sort of ROM to store 7 segment digit lines.

    A nightmare with only the basic gates, but possible. Much easier if you can use the 74xxx logic, use a keypad scan IC and a 7 digit driver IC, with a bit of extra logic to decide which digit needs to be updated.
     
  6. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
  7. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    thank you all for your participations
    but in this project you must not use pic microcontroller

    the only thing you must use is

    decoders, encoders, multiplixers, demultiplixers, and roms only

    it is a challenge for you all
    let us see what you can do>
    thnx
     
  8. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Ohh Man, you will be wiring something like a supercomputer... Good Luck..
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    I already passed that class a few decades ago. :)
     
  10. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    sorry,
    i forgot to tell you that i dont need it to display the whole numbers from 0 to 99

    it is enough to have only some samples
    at most three samples
    that is i want to display
    3, 55, 38
    only those
    or any three numbers you choose
     
  11. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    So you need to display 3 numbers using 3 buttons?? Like when u press a button, it displays 3 and when u press another button, it displays 55 with a single keypress and another button press clears this and displays 38??

    If this is what you want, a few diodes, resistors, 2 displays (and 3 flipflops) will do the job..
    If its using a 3x3 keypad and display like a calculator for each press, its a headache...
     
  12. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    will it is using a 3x3 kepad and tteo 7 segments
    and i dont want it to display 38 by single press
    it displays 38 by pressing 3 and 8
    and you cant use flip flops or latches or pic
     
  13. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    You can't even use flip-flops?? Only Gates?? What all can you use??
     
  14. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    wire the button combinations each to an OR gate and drive the necessary segments using diodes but latching is necessary to hold it on.. That is the most simple option I can think of..
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    No latches or flip flops pretty much stops the design, as stated above, the display would only show a digit while a single button was held down.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    According to your professor's assignment, right?
    No, it is a challenge for you by your professor, abuarab88.

    This is a homework assignment. We cannot do it for you.

    If you get stuck, we might help.

    But we won't do your work for you.
     
  17. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    We tried to help but it appears you are the professor and its our project.. just kiddin.. start by yourself.. we'll help when you need it..
     
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