12 Hour digital clock

Discussion in 'Homework Help' started by Jerun Hapuarachchi, Jun 7, 2015.

  1. Jerun Hapuarachchi

    Thread Starter New Member

    Jun 7, 2015
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    i'm making a 12H digital clock and when it resest at 12 it does not go to 1 instead it goes to 0, How would i get 1 intead of 0?
    Can i use 74ls192 with registers preloading?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Jerun Hapuarachchi likes this.
  3. Jerun Hapuarachchi

    Thread Starter New Member

    Jun 7, 2015
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    i can not understand it. i want some knowledge to use 74ls192 ic...
     
  4. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Why couldnt you use register preload? Detect the zeros and then load the counter with 1. Note you have to detect both zeros in the two leftmost digits, or if you are already detecting a "13" then that will do it too, just load "01".
    So the count should go:
    1258
    1259
    1300
    then load the 01 in:
    0100
    then stop loading and then:
    0101
    0102
    etc.
     
  5. Jerun Hapuarachchi

    Thread Starter New Member

    Jun 7, 2015
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    i cannot understand :(
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    Way back in the 70s, Henry's radio used to include a circuits collection in the back of their catalogue - one project was an entirely TTL digital clock.

    One popular author: Don Lancaster had both CMOS and TTL Cookbooks published, I think one of them may have included a clock project.
     
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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  8. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Tell me how you are working this out to begin with, when it goes to 0000 instead of 0100.
    The count goes:
    1258, then one minute later 1259, then i guess yours goes to 0000 instead of 0100.

    So somehow it must already know how to do that, and what i need to know is what causes it to do that. This is because how you modify it depends partly on how you are doing it already.

    But in general, you 'detect' the count you want to change with logic gates (or some other method) and so when that count appears you can load the counter with the right value.
    For your counters the left most two digits are going to 00, so you detect that with gates or whatever, then load at least the one counter with "1", so you end up with 01 in the left most two digits. That gives you the time display of one o'clock which would look like 01:00 on your display, instead of 00:00 which you seem to have now.

    Usually this will happen fast enough so you dont have to worry about missing any minutes (or seconds), even if you are counting seconds as well as minutes and hours.
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Can you show your schematic as it exists?
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    I never used one of Lancasters schematics as the ICs arent sold anymore and too complicated.

    But after reading the book, I made a circuit with 20 CMOS ICs and LCD. Took me two weeks back then, and costed a fortune.
     
  11. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Yes some of those older circuit methods cost money because there are so many chips involved. I once built an 8 digit frequency counter, with individual 4 bit counters and individual 4 bit latches and individual gates for multiplexing the 8 digit LED display. Counting the chips, that's 24 IC chips not including a few more for the glue logic and clock generator.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    My counter started life as an industrial digital tachometer - the firm I worked for had just acquired a competitor, they piled all the stuff they considered junk in a loading bay with a notice: "Help yourself". There was a fair bit missing from mine after I'd done a few up and sold them, the timebase was straight from one of the D. Lancaster cookbooks. The original had 7-segment neon displays - which I ran out of that weren't punctured. I didn't have enough 7-segment LED digits all the same size to complete mine, so 2 tall ones for the most significant digits and a couple of tiny calculator size digits at the other end.

    The decoder-driver chips for the neon digits couldn't handle LED current, so I ended up with about 3 stacked veroboards for discrete transistor drivers. It was all getting a bit out of hand, I'd bolted 2 chassis together to house the SMPSU I used instead of the original linear.
    Eventually it developed intermittents in the display drivers - I was going to get around to fixing it, but I got a commercial counter cheap at the local tip.
     
  13. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hello again,

    That sounds interesting too.

    For mine, believe it or not, i used the output from standard TTL gates (not LSTTL but the standard family TTL gates) to drive the LED display. The digits were small so they lit up good enough to see with a small, decorative hood mounted on the front panel. These LEDs were only 0.2 inches high and came in a row of 3 or 4 LEDs in one dip package. I still see them for sale now and then on the web. Red LEDs of course, as back then (sometime in the 1970's) they didnt make anything other than red.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    The ones I used were about 0.2" high, but they were individual digits. Having laid out the Veroboard for (mostly) 0.5" digits, I had to solder on like a home made lead-frame to mount the tiny ones.
     
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