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7490/7447 24-Hour Digital Clock

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cacophony, Mar 11, 2010.

  1. cacophony

    cacophony New Member

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    Hi! I attempted to make a schematic of a 7490/ 7447 24-hour digital clock based on research. I was just wondering if anyone could verify my schematic if the circuit would work out smoothly? Please see attached file. Thanks!

    Nicko
     

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    Last edited: Mar 12, 2010
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    There are a number of errors on the circuit, it would take a while to check thru it all.

    But as this clip shows you have two outputs connected together.
    AAesp01..gif
     
    Last edited: Mar 12, 2010
  3. cacophony

    cacophony New Member

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    Oh... What should I do about it then? Sorry... I'm just a newbie.
     
  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Look at this Forum link: http://www.electro-tech-online.com/threads/ttl-clock-with-7447-7490-and-7400-ics.25628/

    Also Search the Forums for 7490 it will bring up lots of clock circuits
     
  6. cacophony

    cacophony New Member

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    OK so I applied the frequency divider with 7490 (MOD-6 counter for tens of second and minute section and MOD-3 counter to the tens section of the hour section). Kindly check out the modified schematic and tell me what you think. Thanks!
     

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  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Look at this clip from your circuit.

    BTW: link 3,4,5 's together on the 74LS47 while testing.

    If you have not bought the 74LS90 look at the 74LS92 for the '5's they are a 2+6 divider.
    Use the 6 divider section for the 'tens of sec'

    clkSec1..png
     
  8. cacophony

    cacophony New Member

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    Hmmmm... Do I have to use an AND gate to it?
     
  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    While you ponder about the gating, how are you going to set the clock time.??

    I ask this because the setting of the clock and the gating for the 'tens' are inter connected.:)

    Do you follow.?
     
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Look at this LTspice simulation of the seconds and minutes section of your clock.
    I have used a HCT390 counter as I dont have the LS90 model, but the action is the same.

    You have to consider how you will set the clock to the local time after power up.

    Also work out the decode for the hours,, 00 to 19 thru 20 to 24 [reset all the chain]

    390cntr1..gif
     
  11. cacophony

    cacophony New Member

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    I've modified the circuit already. Kindly check out the attached file and tell me what you think. Thanks.
     

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  12. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I will look it over, it could be tomorrow before I have the time.:)

    Did you work out how to set the clock to the local time.???

    There is no point in just adding gates in order to get the '5s' working when you will have to modify that circuitry in order to adjust/set the time.OK.?
     
  13. cacophony

    cacophony New Member

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    Oh! I haven't thought about it. Thanks for letting me know.:)
     
  14. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    When you have drawn the complete circuit, showing the Time Set logic, post it so that we can check it out.

    I have used this method in past.
    1. A Set time button.
    Pressing and holding down this sets the Seconds to 00.
    Enables a faster clocking pulse.

    2. Set Minutes button.
    Pressing this [with the Set Time button still pressed] steps the minutes thru from 00 to 59 [repeating] at the faster clock rate.

    3. Set Hours button.
    Pressing this [with the Set Time button still pressed] steps the hours thru from 00 to 24 [repeating] at the faster clock rate.

    Releasing the Set Time button starts the clock running.
    Its easy to sync the seconds to '00' when setting the clock.

    OK.?
     
    Last edited: Mar 14, 2010
  15. cacophony

    cacophony New Member

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    I have a quick question, the latest circuit I posted in PDF format is guaranteed working right? How do I utilize the set button, set minutes button and set hours button with my latest circuit?
     
  16. cacophony

    cacophony New Member

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    A quick question though, excluding the time set logic, is my latest schematic diagram guaranteed working?
     
    Last edited: Mar 15, 2010
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I will check the '24hr' reset, the '5's look OK.

    EDIT:
    The hours will reset on '39:00:00"..

    Hint: you need to detect '24' , so that 1 wire from hours units '4' and a wire from hours tens '2'
    thru an AND gate..[or if you prefer R0/R1 resets] .OK.:)
    AAesp04..png
     
    Last edited: Mar 15, 2010
  18. NickImpers

    NickImpers New Member

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    how is his done then? i need help with that too. could you explain a little more ?
     

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