Need Help with Alarm Clock Circuit

Discussion in 'The Projects Forum' started by scott367, Jul 11, 2008.

  1. scott367

    Thread Starter New Member

    Jul 7, 2008
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    I am designing a digital clock with binary counters for a digital electronics class. I can not figure out how to get the divide by 12 hour section. I am having trouble having the counter reset at 9, then reset again at 12. I am also having trouble presetting the counter to a 1, but letting it go to 0 for 10, then presetting back to 1, since there is no hour 00 , I want it to go 01, 02, 03, 04, 05, 06, 07, 08 , 09, 10, 11, 12, 01....
     
  2. theamber

    Active Member

    Jun 13, 2008
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Are you using 4000 series CMOS, or 74xx series TTL devices, or something else?

    Are binary counters necessary, or can you use BCD counters?

    Since this is a homework assignment, we certainly can't do it for you - but show us what you've done so far, or at least tell us the parts you're trying to use and how you hooked them up.

    Attaching a schematic in .PNG format would be a great way to start.
     
  4. scott367

    Thread Starter New Member

    Jul 7, 2008
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    I am allowed to use either CMOS or TTL, so far I have chosen 74 series TTL because those are the chips that the school has already given us. I am allowed to use decade counters, but one requirement of the clock is that it has to have a settable alarm. Because it has to have an alarm, and because I have to preset the hour section to 1 I wanted presetable counters. I have not been able to find a good presettable decade counter, there are many more presettable binary counters. I have attached the drawing just for the second hand, which is identical to the minute hand , the components aren't labeled, but the counters are 74163N connected to a generic BCD to 7SEG decoder. The points go directly out to the 7 segment display. My problem is when I connect an AND gate to reset at 9, then another AND gate to reset at 12 they don't work for some reason. After looking at a few examples that on the internet I am starting to think that it is just a problem with multisim. Has anyone else used multisim to design and simulate circuits? and do you run into problems when simulating? every time I think that I get it right it says SImulation error timestamp too small. I will attach the hour section later today after I clean it up a little and maybe get it working. Another question though after I get the hours working is how to go about getting started with the presetable alarm circuit. Thanks for your help
     
  5. scott367

    Thread Starter New Member

    Jul 7, 2008
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    Here is the actual part I needed help with, I have it working , it resets at 12, this time with decade counters. It seems anyone I ask for help from suggests decade counters. The only problem is how to get it to start the count at 01, and still be able to go to 10. Any help would be greatly appreciated. These are TTL generic parts that multisim.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You're close. :)

    Big Hint: Rather than using the reset (CLR) input, consider using the preset (LOAD) input.

    Read the datasheet for the 74xx160 through 74xx163 counters, and look at the timing diagrams.
    Link: http://www.ti.com/lit/gpn/sn74ls163a

    Tip: Try to use exact part numbers in your simulator rather than generic parts; you will get more accurate results.
    BCD to 7 Segment: 7447, 74x247, 74x447 - ask your instructor if those are available. The 7447 has been obsolete for years, and is very hard to find outside of the academic world.
     
    Last edited: Jul 12, 2008
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