Unusual clock timing

Discussion in 'The Projects Forum' started by adriano08, Aug 21, 2010.

  1. adriano08

    Thread Starter Member

    Apr 25, 2010
    I designed a clock that comes with hour, minutes and 2 LEDs for seconds display.

    Eg. My clock look something like this: 1:30

    The PCB is working and running smoothly. However after some testing and linking my clock to the rest of my PCBs, it became unusual.

    The seconds supposed to flash 60 times before it carrys forward to 1 minute. It worked pefectly before that. But somehow it runs flashing 30 times instead before it turns 1 minute. The counting of seconds literally changed from blinking 60 times to 30 times.:confused:

    I tested my clock PCB alone time and time again, it still the same.

    Anyone knows or could suggest any possible solutions to this?:)

    I am using 74LS161 and 74LS47 by the way.
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    can you post a schematic of the way you have it built and maybe a photograph of the improperly working PCB layout?
  3. gootee

    Senior Member

    Apr 24, 2007
    Do you have an oscilloscope?

    What signals etc are you linking to the other PCBs, exactly? Have you measured the DC power rails, before and after linking to the other PCBs? Does it change the ground routing, when you connect to the other PCBs? Do you need some buffers, maybe?

    Do you have local bypass capacitors at each chip's power pins and larger capacitance where power enters each PCB?

    Are the connections to the other PCBs very short in length?

    A photo of the whole setup would be helpful.
    Last edited: Aug 21, 2010