Decade Counter

Discussion in 'The Projects Forum' started by swinny, May 3, 2009.

  1. swinny

    Thread Starter New Member

    May 3, 2009
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    Hi, I was just wondering if there was a counter the same as a decade counter but which went up to a higher amount of outputs (say about 100, at least 60). My project is going to be a clock which is run from a 555 astable with pulses every second. This goes into the 'decade counter' and changes an LED output around edge of clock (for the seconds). At the 60th output it will also output onto a second 'decade counter' which then moves up one LED each minute and the same for hours. I hope you can understand, I may not have explained very well :D. My first thought was just to have 6 decade counters each with an input from a single decade counter, however I realised that it would mean I would have 6 LEDs on at any one time. This may look alright for the seconds going round in a circle but the minutes and hours... not so hot. Any ideas would be greatly appreciated. Thanks in advance, Sam.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    You can have more than one decade counter in a chip using the CD4518.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Actually, I believe that our OP is referring to the 4017 5-stage Johnson decade counter instead of a BCD counter.

    I'm not aware of any "extended Johnson counters" of that type. However, you can cascade multiple Johnson counters using AND gates to just about any number of outputs you wish. Unfortunately, with the 1st cascade you lose 1 output, and with the subsequent counters you lose 2 outputs. For 60 outputs, you would need eight 4017's (8 IC's) and seven AND gates (two IC's).

    Here is a schematic from Motorola's datasheet on how to cascade 4017's:
    [​IMG]

    You would be much better off to look at using a microcontroller and Charlieplexing the LEDs.

    Check out Wikipedia's entry on Charlieplexing:
    http://en.wikipedia.org/wiki/Charlieplexing
    It even has a photo of an LED digital clock that looks just like what you're considering.
    Using just 12 I/O pins on a microcontroller, you can control up to 132 LEDs, which would give you 60 LEDs for the seconds, 60 for the minutes, and 12 for the hours.
     
  4. swinny

    Thread Starter New Member

    May 3, 2009
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    Thanks Bill, that might be helpful. Would you mind just explaining how it works and how to wire it briefly as i didn't really get the data sheet. Thanks.
     
  5. swinny

    Thread Starter New Member

    May 3, 2009
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