Digital countdown clock

Discussion in 'General Electronics Chat' started by cableguy, May 26, 2006.

  1. cableguy

    Thread Starter New Member

    May 26, 2006
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    0
    I seem to be having trouble designing a 30 minute countdown timer. Building a timer to count up to 30 minutes, however, is no trouble. Articles I have read is very vague in describing the design process. This clock is using minutes and seconds. Can anyone help me?

    Regards,
    Cableguy
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I can think of at least four different ways to do it.

    1. Binary down counter with BCD Conversion and display.
    2. BCD Down Counter with direct display.
    3. FPGA using VHDL or Verilog.
    4. Microcontroller with display.

    Can you tell me what I have to work with?
     
  3. cableguy

    Thread Starter New Member

    May 26, 2006
    3
    0
    I wish to use jk flip-flops if possible.
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    From the list Papabravo has provided I would personally advise using a Microcontroller with a couple of 7-segment displays. PIC microcontrollers are highly-suitable to develop counterdown timers using the integrated timer module on-chip. Most of the PICs employ at least an 8-bit timer/counter module and in many cases have a 16-bit version. You could get your hands dirty doing this in assembly language or could use a high-level language such as C.

    If you choose to look at using a PIC microcontroller you can develop your countdown timer using the MPLAB software, available from Microchip.

    As for your idea of using JK flip-flops, is there any particular reason you wish to use such components?

    Dave
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Gotta agree with Dave. The sheer number of j-k flip flops needed for the function is huge.

    Look up a parallel-load up/down counter datasheet (in whatever logic family you are planning to use), and life gets lots easier.
     
  6. cableguy

    Thread Starter New Member

    May 26, 2006
    3
    0
    In stead of using the microcontroller could I use 74HC192 (Presettable Synchronous Up/Down BCD Counter) to do a 30-minute count down?

    Thanks,
    Cableguy
     
  7. Papabravo

    Expert

    Feb 24, 2006
    9,910
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    That should work just fine.
    Good Luck
     
  8. BladeSabre

    Senior Member

    Aug 11, 2005
    105
    0
    I noticed that this timer has to count seconds too, which is a bit more complicated than just a counter. (I'm not sure about this, but I was thinking it might need two counters. And a little logic to load the seconds counter with 59 after it hits 0.)

    Edited to add: the 74HC192 is only one digit anyway. So... that's not a problem really. Just the high seconds digit needs to go to 5 after 0.
     
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