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1Mhz -> 1hz What chip should I use?

Discussion in 'Electronic Design' started by Eric, Feb 6, 2004.

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  1. Eric

    Eric Guest

    I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
    to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
    chips for most of the clock. What would be the way to do this with the least
    amount of chips? If it's possible specific chip numbers would be nice.
    Thanks in advance.
  2. Leon Heller

    Leon Heller Guest

    You could do the whole clock with a single CPLD and a 1 MHz oscillator.

  3. Tim Wescott

    Tim Wescott Guest

    We have to know your ground rules. "Least chips" these days would be to
    build the whole clock using one FPGA, one CPLD or one microcontroller. As
    your previous posts indicate you're doing this for a class and either can't,
    or don't want to, take that approach (although CPLDs are pretty cheap these
    days, and with Xilinx CPLDs at least the tools are free as well).

    If you must start with 1MHz then you're pretty much limited to dividing by
    powers of 10. If you must use discrete logic then using six 74LS90s or
    three 74LS390s is probably best. If you can use 1.6384MHz then you can use
    one 74HC4040 (which also has an oscillator section) to get down to 100Hz and
    one 74LS390 to get to 1Hz.
  4. John Fields

    John Fields Guest

    A cheap micro would get you there with a single chip and, in the
    bargain, do pretty much everything else.

    You could also get there with six 'LS90's:

    | +--------+ |
    +--|>CKA QD|--+
    | |
    +--|>CKB QA|-------->1Hz
    | +--------+
    +--------------+ |
    | +--------+ | |
    +--|>CKA QD|--+ |
    | | |
    +--|>CKB QA|----+--->10Hz
    | +--------+
    +--------------+ |
    | +--------+ | |
    +--|>CKA QD|--+ |
    | | |
    +--|>CKB QA|----+--->100Hz
    | +--------+
    +--------------+ |
    | +--------+ | |
    +--|>CKA QD|--+ |
    | | |
    +--|>CKB QA|----+-->1000Hz
    | +--------+
    +--------------+ |
    | +--------+ | |
    +--|>CKA QD|--+ |
    | | |
    +--|>CKB QA|----+-->10kHz
    | +--------+
    +--------------+ |
    | +--------+ | |
    +--|>CKA QD|--+ |
    | | |
    1MHz>--|>CKB QA|----+-->100kHz

    Or you could use three '390's, or two '4059's, or...
  5. Bill Sloman

    Bill Sloman Guest

    If you can't use a programmable logic device, the 74HCT40103 is an 8-bit
    programmable divider, so you can set up three of them in series to divide by
    100 each.

    Farnell also seems to stock the 74HC40103 and HCF40103, if you don't
    actually need TTL compatibility.

    Farnell also stocks the LSI LS7060 32-bit binary up counter, and the LSI
    LS7166 24-bit multi-mode counter. Some fifteen years ago we used the LSI
    7166, and I think you might be able to use it as a divider. I've not been
    able to locate a data-sheet, so I can't be sure.
  6. Ken Smith

    Ken Smith Guest

    Check out the CD4059 or 74HC4059
  7. Bill Sloman

    Bill Sloman Guest

    gives a data sheet for the LS7166 24-bit multi-mode counter/divider, It is
    designed to be driven by an eight-bit bus, so it needs some sort of
    microcontroller to set it up. Weird part but Farnell has stocked it for some
    15 years now, so somebody must be using it.
  8. I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need

    Why are you using this relatively high-speed crystal, by the way? It's
    easiest to divide by a power of two, and the less division you have to
    do, the fewer chips. That's why the vast majority of clocks and watches
    use 32.768kHz crystals and 15 flip-flops to divide it by 32768.
  9. mike

    mike Guest

    That ought to give you enough pins to drive the kbd/display
    directly and enough flexibility to add features.

    Return address is VALID.
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  10. Wim Ton

    Wim Ton Guest

    I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
    2* 4040 12 stage CMOS divider and 1 * 4068 8 input NAND

  11. Though he says he has an 'oscillating crystal', if this means he just has
    the crystal, another chip will be needed for the oscillator, or if one is
    allready being used, a chip could be saved. The 4060, could be used instead
    of the first 4040, which gives an oscillator as well.

    Best Wishes
  12. Bill Sloman wrote...
    LSI Computer, Melville, NY.

    They still make all those cool cool chips. I used to order
    a few hundred RED50/60 chips every year or so at Sea Data.
    That was 20-to-25 years ago and they still make all of them.

    - Win

  13. I would be tempted to ditch that 1MHz crystal and use a 32768KHz crystal
    with a trimmer and a 4060. Also, if the OP meant a 1MHz crystal oscillator,
    such as those square canned ones, he might discover that the accuracy
    of the clock can be a bit dissapointing. 6 seconds per week is not unusual.
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