Generating a 1 Hz clock?

Discussion in 'The Projects Forum' started by BlackCow, Feb 1, 2010.

  1. BlackCow

    Thread Starter Active Member

    May 11, 2009
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    I was interested in making a digital clock out of 74* series chips. The only thing I am stuck on is generating a precise clock cycle. I'm assuming a 555 is no where near accurate enough.

    I was thinking about using a crystal, but I have no clue how to make one work, or how to divide one down to 1 Hz.

    Could someone point me in the right direction? I don't mind ordering another type of crystal but the ones I do have on hand are 8 MHz and 4 MHz.

    Update: If anyone stumbles upon this thread I did eventually build this clock using a quartz clock circuit as the time base. Thanks for the advice jgessling!
     
    Last edited: Apr 2, 2010
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Hack a $4.95 battery-powered wall-clock. The hands are moved by a two-coil stepping motor. Each winding is pulsed at 2Hz, starting from a 32Khz crystal. Stability is within a few seconds per year...
     
  3. jgessling

    Active Member

    Jul 31, 2009
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    14
    I've been running my TTL clock on the breadboard for a few days now and I'm very pleased. I used a crystal from an old battery powered clock as seen on this site. http://www.josepino.com/?one_second_timebase
    Look down to the modification schematics. Mine is like the one with the transistor except instead of a LED I used two diodes in series to give 1.4v across the crystal. Since the battery would give 1.5v maximum I thought it best to stay below that. Not sure that's a big deal though, try it out. Keeps real good time too. Search this site for previous discussions of this topic.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Actually the two pulses are 0.5Hz, 180° out of phase.

    ken
     
  5. BlackCow

    Thread Starter Active Member

    May 11, 2009
    65
    1
    Is there anyway to do it with an 8 MHz crystal?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Woah. You would need some serious division. Its possible, but over kill. Have you read the josepino link? It works great. I get the clocks from the dollar store, for a dollar.;)
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
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    If you are going to be using a wal-wart for power, use an AC 'wart. Divide the line freq by 60 and you have super accuracy.
     
  8. BlackCow

    Thread Starter Active Member

    May 11, 2009
    65
    1
    I think I'm going to go with the cheap dollar store clock hack haha. Thanks for your help guys.

    Edit: Good news, I found an old micky mouse battery operated clock, perhaps I can incorporate micky into my design XD
     
    Last edited: Feb 1, 2010
  9. jgessling

    Active Member

    Jul 31, 2009
    74
    14
    I did have trouble at first with the junk clock circuit. An LED would flash fine but the pulse wouldn't clock my chips right. Put the output from the crystal into a 7414 (schmitt trigger inverter) and the output of that worked fine. Hope this helps.
     
  10. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    This will also work.

    Ken
     
  11. BlackCow

    Thread Starter Active Member

    May 11, 2009
    65
    1
    So I tried using the circuit on that site, when I ran the two half hertz cycles through diodes I couldn't get a pulse out the other end, but when I took the two clock lines, tied them together into my decade counter it worked fine! Each line was about 2.3 volts so I guess added together they are pretty much a TTL 5 volts.

    Thanks for your help guys!
     
  12. jgessling

    Active Member

    Jul 31, 2009
    74
    14
    Looks just about the same as mine, thanks. Can I ask you what you used to draw that schematic? I'm looking for just a simple drawing tool, I've used several things for simulation: ltspice and hades they were very good and I tried Eaglecad (too small limitation) and ExpressPCB (too limited parts) for drawing and both are pretty hard to learn. I am now just looking for something to draw my schematic so I can save it before going to the soldering stage. This is my first real project and so I am worried that I will lose the design when I make this transition from the breadboard.
     
  13. HeliEye

    New Member

    Feb 6, 2010
    9
    0
    Nice and simple circuit, TTL level out and the sneaky 4148 'zener' reg :)

    Steve
     
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