Building a Digital Clock

Discussion in 'The Projects Forum' started by Slasherbaven, Jun 23, 2008.

  1. Slasherbaven

    Thread Starter Member

    Jun 23, 2008
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    I need to build a digital clock using gates.
    I'm not going to ask for schematics or anything, but what all do I need to know (and understand) in order to build it?

    For one, I know it requires a common anode/cathode, a 555 timer and a couple of ICs.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Uh, it's a bit more complex than that. Instead of gates, think counters, aka flip flop, registers, or ripple counters. I think it can be done better, but Bill Bowdens website has some good ideas.

    http://ourworld.compuserve.com/homepages/Bill_Bowden/
    http://ourworld.compuserve.com/homepages/Bill_Bowden/dclock.htm

    If you do decide to home brew your own pay special attention to his 32767 crystal oscillators. This is a magic frequency, since 32768 is basically 2^15, in other words a straight 15 bit ripple counter will yeild an accurate and stable 1 hz time base. Never built it, but I've designed my own using individual counters.
     
  3. Slasherbaven

    Thread Starter Member

    Jun 23, 2008
    13
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    Thanks for the reply, Bill.
    Unfortunately, I'm still hazy about the whole thing, mainly because I only just recently learned about gates.

    Besides the ones you've mentioned, as well as the one in Bowden's site, what else do I need to know to understand what I'm doing better?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Focus on counter circuits. There are a ton of different types of counters. The core component of any counter is a flip flop. These come in several flavors too, but fundimentally you pulse one with a singe wave and it flips, pulse it again and it flops. This is a single bit counter. Add 3 more, each feeding the one after, and you have a 4 bit [url="http://www.allaboutcircuits.com/vol_4/chpt_11/index.html]counter[/url], which is 0 - 15. Adjust the design to reset once it has hit the high end number and you have a digit for a clock, say 0-5 or 0-9.

    The AAC eBook has some good paragraphs on the subject. I've linked to it in several places in the above paragraph, I would recommend some reading. All a clock is is a specific type of counter. Good Luck.
     
  5. Slasherbaven

    Thread Starter Member

    Jun 23, 2008
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    Thanks a lot for the information, Bill.
    We made a circuit, I can't draw it but I'll try my best to explain it.

    We used four 7447 and four 7490, connected in a pair each to the seconds and minutes representative of four common anodes.
    A 555 timer(where two variable resistors were used instead of a normal one to adjust the speed of the timer) was used to generate the square wave of 1Hz.
    So it is connected like this:

    555 -> 7490 -> 7447 -> Common Anode

    So we successfully created a timer.
    However, there are two problems present:
    [1] Circuit requires a lot of energy.
    [2] The hour part of the clock is still undone.

    What could I do to reduce the energy consumption, and any hints on how I can control the hour timer? As in, for one common anode, the time needs to go from 0~9 for the first cycle and 0~4 for the second.
     
    Last edited: Jun 24, 2008
  6. Wendy

    Moderator

    Mar 24, 2008
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    OK, you're almost there. Check out the 7490's twin, the 7492. The 7492 is to a divide by 12 what a 7490 is to divide by 10.

    You have made (or will make) a 00-59 counter. You now need to make a 01-12 counter, or a 00-23 counter (or one that can convert between the two modes). So what will it be?

    As for power, there are several ways of handling that, where is your power going, the display? If that is where you are talking about I can show you a few tricks, but understand, LEDs do require some current.

    If it is the rest of the circuit you're talking about the answer is simple, look for the CMOS equivalent of the 7400 family. CMOS chips draw almost no juice, though the price is in how much current they can source out.

    Don't have much time at the moment, so I'll have to get back with you in about a day. I have an untried, untested schematic of a clock I was thinking of making (my design) I'll attach then. It might give you some ideas.

    Just a suggestion, go to my AAC blog (there is another link is next to blog entries), and download PaintCAD, and look for the sheet labeled pinouts. You might find some other interesting ideas there.
     
  7. Slasherbaven

    Thread Starter Member

    Jun 23, 2008
    13
    0
    This might be a bit too late, but thanks for the time, Bill.
    You've been a great help!
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Take a look at a CMOS 4518B IC. They are dual BCD UP-counters.

    There's also the 4026 and 4033 IC's, which have built-in 7-segment display drivers. Might be hard to find nowadays.
     
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