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TTL Clock with 7447 7490 and 7400 IC's

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by RODALCO, Nov 28, 2006.

  1. ibryazici

    ibryazici New Member

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    how to with 555

    i am trying to build a digital clock without seconds. so i need to use a 555 to generate 60 hz and connect it to 7493 for minutes. but i could not design it. could any body help me pls.. thanks
     
  2. blueroomelectronics

    blueroomelectronics Well-Known Member

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    It'll be very inaccurate as the 555 is not a good timebase. The CD4060 can handle a crystal which might make it better suited.
     
  3. RODALCO

    RODALCO Well-Known Member

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    ibriazici Just build the clock with the two 7490 IC's for the seconds but don't attach 7447 ic's and 7 segment displays to them.

    A 555 is not accurate via a timeing cap as already said by blueroomelectronics.

    zajioftheasuka, To get your clock to start at 00:00 you need to reset at all the R0 and R9 gates of the 7490 IC's.
     
  4. dave

    Dave New Member

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  5. RODALCO

    RODALCO Well-Known Member

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    The circuit drawn is all with 7490 IC's, because these are easier to get, it may be why your circuit doesn't work.

    A 7492 is a 2, 6 and 12 divider. The clock schema is different if you built it with these IC's and you don't need the 7400 gates to divide out the 6.
    I see if I can find a 60 counter with those ic's.
     
  6. silvarblade

    silvarblade Member

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    see howstuffworks.com. search

    'How digital clocks work' (its heavy n ive got a dial up connection).
    they have got a digital clock made with 7490. mod6 and mod10 u name it. with out the use of any gating circuitry.
     
  7. RODALCO

    RODALCO Well-Known Member

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    Some data from the TTL IC 7492 is attached.

    Bear in mind that the 7492 only gives a BCD code off from 0 to 5.
    (see truth table)

    Source: ( Digitale Klokschakelingen, Herbert Bernstein )

    Regards, Rodalco
     

    Attached Files:

  8. Pete61

    Pete61 New Member

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    TTL Clock

    Hi All,

    I need help with designing a clock with old the 7400 series IC's. I have a 1 MHz crystal "can" oscillator (4-pin).
    How can I use this to drive seconds, minutes and hours.
    I have tried basic design but it is not working. HELP!!!!!!
     
  9. RODALCO

    RODALCO Well-Known Member

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    Are you sure that your crystal is working ?

    If yes, you have to divide the output it to get the 1 Hz frequency .

    Inefficient but it works, is to divide it with 6 x 7490 IC's to 1 Hertz. It is probably easier to get a standard 3.2768 MHz crystal and divide it by 16.

    To test your clock use the 50 Hz mains frequency double it via a bridge rectifier to 100 Hz via a small 5 or 6 Volts transformer.
    Take off signal via a 1 K 0hm resistor ( I draw you a sketch later , teatime sorry ).
     
  10. MRCecil

    MRCecil Member

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    Hi Pete,

    You didn't say what Vcc was for your oscillator, but the attached ckt. will operate OK at both 3.3V and 5V. It's just three cascaded '390's configured for 100 division per with the output at 1 Hz at 50% duty cycle. It should fit the bill.
     

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  11. RODALCO

    RODALCO Well-Known Member

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    Ttl

    Here are the promised schematics.

    One is how to make an oscillator with a 7400.
    Others are for 50 and 100 Hz ripple to drive clock circuit instead of crystal.

    Regards, Raymond
     

    Attached Files:

  12. Pete61

    Pete61 New Member

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    Thanks for the help but I still have a problem! The canned oscillator I am using will only drive 10 TTL Max. I got it to work the seconds, however, it will not clock minutes.

    Is there any way to boost or amplify the crystal's output?

    I am using the old 7400 series IC's. Would changing to 74HC work better?
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    74xxx ICs have a max input current of 1.6mA. 10 have a lot of current.
    74HCxxx ICs have no input current. But might not detect a high from a 74xxx.
    A 74HCxxx can drive only 2 old 74xxx inputs.
     
  14. cls_tec

    cls_tec New Member

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    Help with 74ls90 counter

    I built the second "ones" hand of a 74LS90 clock.But it seems to be stuck.but if I remove power and plug back in , then it changes.Could somebody advise how to resolve this problem?

    thanks
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    All digital circuits need a circuit to reset them when the power is applied.
     
  16. cls_tec

    cls_tec New Member

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    Let me go into more detail. I nuilt it from this page http://electronics.howstuffworks.com/digital-clock6.htm

    My timebase is the 60Hz line from AC mains.I plugged power in, but the leds seems stuck, no counting.They just dont move.It seems like something the preventing the counter from counting.

    Could somebody please advise on this problem , Thanks a lot.
     
  17. cls_tec

    cls_tec New Member

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    never mind my above question, I decoupled all power leads with .1uF and rebuilt the whole thing.I connected leds to QABCD checking for binary out. So it works now . thanks.I still dont know whether It is working right , since I cant read binary!
     
  18. RODALCO

    RODALCO Well-Known Member

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    Decoupling all IC's is a must with TTL. (0.1µF or 100nF ceramic)

    The IC's draw small surges in the 5 volt supply during switching which may trigger an input of an other IC hence erratic readings.

    As cls tec sais use 74LS90 IC's.

    I'm not sure what pete61 means with the canned oscillator ?
    The output from the crystal is normally going to the divider and that output normally only drives one TTL gate.
     
  19. cls_tec

    cls_tec New Member

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    Hi again guys ,

    Canned Oscillators are those square 4 pin metal can oscillators.

    http://electronics.howstuffworks.com/digital-clock4.htm

    Above is the link for the power supply/timebase I built.The only modification I made is using a 9V-0V-9V transformer and used one side(9V-0V).

    So I built some counters to experiment and found that I had to use four decade counters to get it slow enough to get the 0-9 second side.Problem is I dont have enough chips to then get the minute and hour side.It seems like somehow using a 9-0-9 transformer caused the AC line frequency to increase(it should have been 60Hz and I should have to only use 2 chips in divide by 10 and 6 to get 1 Hz and then one more decade counter to get 0-9 second side)

    Thanks again very much,very fun project.
     
  20. Pete61

    Pete61 New Member

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    The canned oscillator I am using will drive 10 TTL max (Load). It oscillates at 1 Mhz. I'm using 6 - 74160's to aquire my 1 hz timebase. 2 - 74160's for seconds, 2 - 74160's for minutes etc...

    I got the seconds to work, but the minutes stay at zero.

    Any Idea's?
     
  21. Pete61

    Pete61 New Member

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    Guess Not!

    A can oscillator has four pins.

    Thank you all anyway. I will continue experimenting.

    The clock is an anniversary present for wife. I have until Aug 1st to complete it.

    I'm sure I will will have it all figured out by then.

    Thank you all again and take care.
     

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