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74C925 alternative?

Discussion in 'Electronic Design' started by jimi, Nov 30, 2006.

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  1. jimi

    jimi Guest

    Does anyone know of an alternative for the 74C925 chip for driving 4x7
    segment LED's. The chip seems to be obsolete. Thanks
  2. I've never dealt with this company, but your 74C925 does show up in a seach.

    Good luck.
  3. Guest

    Use a programmable logic device or an Arizona Microsystems PIC
    processor - I'm not far enough into either option to identify a part
    which comes in the right 16-pin 0.3" dual-in-line package (and it
    might be difficult to find a programmable logic device with enough
    buried flip-flops to do the job in an essentially obsolescent package)
    but somebody will know.
  4. Maxim has some super duper new LED drivers.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  5. Guest

  6. John Fields

    John Fields Guest

  7. jimi

    jimi Guest

    Thanks for the replies, however, I asked the question so I could avoid
    using a microcontroller.
  8. Donald

    Donald Guest

    Thinking out loud,

    With simple CMOS technology going away, wouldn't it be wise to replace
    it with something you can get in a few years.

    Once you get C code running, going to a smaller uC would be easier the
    second time.

    What ever chip you find today, will be gone next year.

    good luck

  9. Guest

    So you wnat the OP to replace a 16-pin DIP with a 28-pin DIP that
    Intersil has marked "inactive".
    I'd prefer a programmable logic part - the 4-digit counter is not
    synchronous with the multiplexing logic for the display. Back in 1972 I
    dealt with this problem by freezing the multipexing clock until any
    incoming count had rippled through the (asynchronous) counters, which
    took up to 4usec. This wasn't an elegant solution. With a
    microcontroller, I guess you'd rely on the interrupt system to capture
    clock increments that occured at the wrong instant, and you'd keep your
    interrupt handler short and quick to keep the maximum count rate

    Programmable logic offers true parallel processing, which can be a lot
  10. Arlet

    Arlet Guest

    Many microcontrollers have built-in timers than be driven from external
    clock. This isn't truly asynchronous, because the external clock is
    typically sampled on the internal clock, but it still allows quite fast
    operation. For speeds <= 1MHz, a cheap microcontroller will work fine.
  11. John Fields

    John Fields Guest

  12. John Fields

    John Fields Guest

    1. I don't "want" the OP to do anything; I presented him with an
    option to the 925 as he requested. Whether he chooses to use
    it or not is entirely up to him.

    2. Whether Intersil has marked it inactive or not, the part is
    currently in production and is available. Digi-Key, for
    example, has 807 pieces in stock, Newark-in-One 236, and I
    suppose if took the time to look further I could find even
    more sources.

  13. Guest

    I don't know what you were doing in 1972 - the fact that you haven't
    yet got past 555's does suggest that you aren't an early adopter - but
    my toy used TTL logic and Beckman 7-segment fluorescent displays, with
    a few transistors to handle the voltage swings.

    And not a filament in sight (nor any hidden filaments either)

    Looked quite neat.
  14. John Fields

    John Fields Guest

    I'd say that statement more nearly categorizes your position than
    mine since I adopted them way back when they first came out. You,
    on the other hand, have yet to use one (by your own admission) so
    I'd say you're the one who's a little late getting on the bandwagon.

    Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.

    Where do you think the electrons used to illuminate the phosphors
    come from, otherwise?
  15. The Beckman displays were flat panel plasma discharge displays, sort
    of like Nixies but segmented and with the segments all in one plane.
    You used to seem them on gas pumps until fairly recently as well as
    some industrial instruments (Simpson had a fairly successful series of
    instruments that used them). National semi made a biplar driver chip
    DS8880 or something like that.. ah, here it is:

    Best regards,
    Spehro Pefhany
  16. John Fields

    John Fields Guest

  17. jimi

    jimi Guest

    It's a one off.
  18. Guest

    discharge" discharge mechanism - in a low pressure of some noble gas
    (probably neon, but I can't be sure) and certainly not fom a filament.
    There was a small, steady "keep alive" corona discharge hdden behind an
    opaque bit of the glass front, and the active segments lit up when you
    hit them with something over 180V, whch would have been around the
    Passchen minimum for avalanche discharge through neon. Without the
    keep-alive discharge, fast multiplexing could be chancey - it was an
    added extra feature in the second generation of the displays.

    Agreed. The Beckman displays were nicer than most but the 180V seems to
    have been unpopular.
  19. jasen

    jasen Guest

    use a microcontroller?
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