Help with digital clock...

Discussion in 'The Projects Forum' started by eehelp, Apr 21, 2010.

  1. eehelp

    eehelp Thread Starter New Member

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    I have to build a digital clock using 74161 counters for my final project, but I'm having troubles. I got part of the seconds to work, but I'm stuck when it comes to the rest of the seconds, minutes, and hours. Here's the schematic of what I have now: http://www.flickr.com/photos/38401311@N05/4541585238/. Thanks in advance!
  2. retched

    retched AAC Fanatic!

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    Bill_marsden has a clock diagram you will want to look at. Search the forum for clock circuits and you will find plenty.

    Ive found the diagram:
    [​IMG]
  3. eehelp

    eehelp Thread Starter New Member

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    I've been looking all over for some examples, but I can't find any. I have to use 74161's for this project unfortunately.
  4. kingdano

    kingdano Member

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    the posted diagram, looks to me at least, like an overall architecture that you can use with any device essentially.

    what it is showing you is an overall topology to apply to your specific devices.

    i think.
  5. beenthere

    beenthere AAC Fanatic!

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    Use "74161" as a search term in Google to get a data sheet. That should answer some questions - like how to get the tens part of the seconds counter to go. Onece you have that, everything else should fall into place.
  6. eehelp

    eehelp Thread Starter New Member

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    I looked at the datasheet, but it doesn't really say anything about how to make different counting sequences...
  7. rjenkins

    rjenkins AAC Fanatic!

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    If I remember correctly, the 161 is a synchronous counter with load.

    To do seconds, minutes & hours you would need two stages each.

    With each two decade section, you have to use a few gates to give a signal at maximum count (eg. 59) and use that to activate the Load input.

    The next clock pulse would then load the value from the input pins (which you set to fixed levels) rather than incrementing the count, so 59 -> 00 or 12 -> 01. (Or 23 -> 00 if you prefer).

    If you are on to counters you should understand simple gates, so start drawing you circuit!


    ps You have already said it's homework, so no one will design it for you - clues and pointers only.
  8. eehelp

    eehelp Thread Starter New Member

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    Thanks for the advice, but I just really don't understand how to make this work. Could anyone give me more specific advice? I switched my major a while ago, so now I just have to pass this class...
  9. retched

    retched AAC Fanatic!

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  10. eehelp

    eehelp Thread Starter New Member

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    Thanks for the link, it did help with resetting the counter so it only counts to 5. So now for some reason the 2nd counter for the seconds is starting to increment when the first counter gets to 8, instead of 9. Here's what my circuit looks like: http://www.flickr.com/photos/38401311@N05/4553827050/
  11. rjenkins

    rjenkins AAC Fanatic!

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    You are using QD from the first stage as clock for the second, That goes High when the count reaches 8.

    The proper way to cascade synchronous counters is to have the clock connected to all stages and use one of the enable inputs to hold the count until you get a 'carry' from the previous stage.

    I think if you invert the '= 9' signal you have already produced, that should work as the second stage count enable.
  12. eehelp

    eehelp Thread Starter New Member

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    Alright I got the counters working now. Anyone have ideas on how to set the clock?
  13. retched

    retched AAC Fanatic!

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    Why set it.. It will be right twice a day.

    You will need a manual (button) to pulse the minute and hour counters manually.

    A button tied to Vcc and when you press the button it hits the clock line for hours

    And another for min.

    Look up switch de-bouncing also.
  14. eehelp

    eehelp Thread Starter New Member

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    Ok, so the switch should be connected to Vcc & CLK of the minutes chip? I tried this, but it doesn't do anything.
  15. retched

    retched AAC Fanatic!

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