Decade Counter Output Pulses (CD4017)

Discussion in 'General Electronics Chat' started by Mosfetti, Aug 27, 2010.

  1. Mosfetti

    Thread Starter New Member

    Aug 22, 2010
    I am a "newbie" to this forum and would like to briefly discuss the pulses from the decoded outputs of a decade counter such as a CD4017B type. The attached timing diagram shows, marked in red at the bottom of the diagram, the width of what I assume is a typical pulse from on of the decoded outputs.

    I am driving the clock input of the 4017 with an adjustable astable configured 555 chip. Th r/c components for the 555 oscillator is selected for a slow clock rate up toabout 500 Hz maximum.

    If the pulse from the astable cicuit is say 25 milliseconds in duration, does it necessarily follow that the duration of the pulse from any of the decoded outputs of the 4017 will also be of the same duration, ie 25 milliseconds?

    If not, is there a methodology to design a circuit adaption to allow the decoded pulses to followeaxctly the pulse duration of the 555 clock signal?

    Thank you.

    "Insanity is doing everything the same way you always have...and expecting different results."
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    If you examine the train of clock pulses you will see that the counter state changes with the positive transition of each clock pulse. If you need an output pulse that mirrors the 555's duration, then you will have to use an AND gate to pass the 555 clock and the 4017 output.
  3. SgtWookie


    Jul 17, 2007
    Note that you will have some propagation delay through the 4017.

    Take a look at Motorola/ONSemi's datasheet for the MC14017; the relationship between the inputs and outputs is much more clearly shown, including where to figure the propagation delays.